How Much Can 9mm Bullet Weight Affect POI (S&W 3913)

[jetinteriorguy]

I have a few different guns that tend to shoot low, at least in my hands anyway. All I shoot are 124 gr bullets, so all I do is either go from a 6:00 o'clock hold to a combat hold or I just triangulate the front sight higher so the dots form a triangle, just depends on the gun. I shoot exclusively handloads and load for the best group and either adjust my sights or my sight picture accordingly for accuracy. All I'm doing is punching paper from 7-15 yds though. I will say, for my carry gun it's right on at 7-10 yds with a 6:00 o'clock hold and for CC wouldn't have it any other way since for me this is an instinctive way to shoot.

 

[45_auto]

Equal but opposite reactions are certainly there, but the difference in the masses of the major components 1) barrel, slide, and less directly, the frame and 2) the bullet being pushed against friction out of the barrel and the force required to move them are hardly equal.

Actually, the forces and momentum are EXACTLY equal. The Kinetic Energy is vastly different since the masses and velocities are extremely different, and the Velocity term is a squared function in the Kinetic Energy equation.

SAAMi Gun Recoil Formula describes it here:

http://www.saami.org/PubResources/GunRecoilFormulae.pdf

Recoil can be described mathematically by the physical law of the Conservation of Momentum. Thelaw states: "lf a force and it's reaction act between two bodies, and no other forces are present, equaland opposite changes in the momentum will be given to the two bodies." Simply stated, this says that for every action there is an equal and opposite (in direction) action. The momentum, therefore, of a free recoiling firearm is equal and opposite in direction to the momentum of the bullet (or shot charge and wad column) and the propellant gases

My old 1963 Schaum's Engineering examples describes it here:

Note problem 20.30, and how it says "since no external forces act...". Barrel friction is an INTERNAL force. Higher barrel friction just means that you need a higher chamber pressure to achieve the same velocity. The additional force required to move the bullet forward against the higher friction is EXACTLY balanced by the rearward force exerted by the higher chamber pressure.

You can also use Force = Mass x Acceleration (Force on the bullet to Accelerate it's Mass to a given velocity at the muzzle) to compute slide travel, slide velocity, etc just like John Browning did it over 100 years ago if you like.

The example below is from an old discussion on 1911's, if I recall correctly someone was trying to claim that they could accelerate the slide by hand to the same velocity in the same amount of time as a bullet. I guess it's technically possible, but only if you're capable of applying about 850 pounds of force!

Math behind the functioning of a 1911 from some previous threads, if anyone is interested.

If anyone is really interested, you can use Newton’s stuff from 400 years ago to understand how your gun works. We used it to get us to the moon back in the 60’s, we use it on the rockets and guns we’re designing today. If you don’t care to know, don’t worry about it, keep believing whatever makes you happy! No big deal.

For example, how long does your bullet remain in your gun barrel, and what kind of acceleration does the bullet experience?

What kind of acceleration does your slide experience, and how fast is it moving when the bullet exits? How far has the slide moved rearward when the bullet exits?

This kind of stuff is REAL important if you’re designing things like rocket mechanisms or artillery fuses or proximity detonators.

Not real easy to effectively transmit mathematical concepts in a forum format, but we can try. I’m going to ignore the contribution of the unburned powder and gases exiting the barrel with the bullet.

We’ll call the starting position of the bullet the zero of our coordinate system, so X(initial) = 0. We’ll abbreviate it as Xi cause I’m lazy. That means Xi = 0.

V(initial) is the starting velocity. We’ll call that Vi. For a bullet in a gun, it’s initial velocity is 0. So Vi = 0.

We’ll call the last position we consider, the end of the barrel, X(final). I’ll abbreviate that as Xf.

T = time in seconds.
T**2 means “T raised to the second power” or "T squared" or “T x T”.
X = position in inches.
V = velocity in feet per second.
A = acceleration in feet per second squared (fps**2).

The basic motion equation in terms of time is:

Xf = Xi + V x T + (A x T**2) / 2

If you want more on this basic motion equation, you can go here:

http://en.wikipedia.org/wiki/Equations_of_motion

Introductory calculus teaches us that the first derivative of position is velocity, and the first derivative of velocity and the second derivative of position is acceleration (I’m not going into calculus for you).

So Velocity = Vi + Acceleration x Time, or

Vf = Vi + A x T

We’ll look at a typical .45 caliber 1911. First thing we have to do is get everything into common units.

Bullet weight = 230 grains = 230/7000 pounds = .033 pounds = .001025 slugs (slug is mass unit in english system).
Barrel length = 5 inches = 5/12 feet = .417 feet
Bullet velocity when it exits the barrel at 5 inches = 830 feet per second.

Now we just use the basic motion equation:

Xf = Xi + Vi x T + (A x T**2) / 2

Put in our 1911 values that we know:

.417 = 0 + 0 x T + (A x T**2) / 2 or

.417 = (A x T**2) / 2 (NOTE – This will be EQ1)

Notice that we have 2 unknowns (A and T) but so far only one equation. From basic algebra we know that we need as many equations as unknowns if we hope to solve them.

This is where we use the rest of the stuff we know and the velocity equation:

Vf = Vi + (A x T)

We know Vf (Velocity final) is 830 fps. We know Vi (Velocity initial) is 0, so

830 = 0 + (A x T)

Since we loved algebra, we solve for A in the above equation and find

A = 830 / T (NOTE – This will be EQ2)

Now we can cleverly plug the above relationship back into our basic motion equation EQ1, replacing A with 830 / T.

.417 = (830/T) x (T**2) / 2

Simplifying this (basic algebra again) gives

.417 = 415 x T

Now we solve for T:

T = .417/415 = .0010048 seconds

In other words, T is right at 1/1000 of a second.

Since we now know T, we can easily solve for A from EQ2:

A = 830/ T = 830 / .001 = 830,000 feet per second squared.

Acceleration due to gravity = 32.2 fps**2, so our bullet is experiencing:

830,000 / 32.2 = 25776.4 G’s as it goes down the barrel.

Kind of important to know if you want to hang some electronics on your bullet. They better be able to handle more than 25,000 G’s.

How much force is the locked together barrel/slide seeing, and how fast is it accelerating?

We know that the force from the bullet equals its mass times acceleration, and we know that for every force there is an equal and opposite reaction (that Newton stuff again).

So the force delivered to the locked together barrel/slide from the bullet is:

F = M x A

F = mass of bullet x acceleration of bullet

F = .001025 x 830,000 = 851 pounds

How fast will 851 pounds accelerate the barrel/slide?

F = M x A = 851

Algebra again:

A = F / M = 851 / M

I’m going to say 1.5 pounds for the slide and .5 pounds for the barrel, mass would be 2/32.2 = .062 slugs.

So the acceleration of the slide is:

A = 851 / .062 = 13695 feet per second squared.

13,695 / 32.2 = 425.31 G's

Now we know the acceleration, so how fast is the slide moving when the bullet exits the barrel?

We know the bullet is in the barrel for .001 seconds, and once it leaves the barrel there is no more reaction with the gun. So the slide/barrel acceleration is applied for .001 seconds.

V = A x T = 13695 x .001 = 13.695 feet per second.

The slide is moving rearward at 13.7 feet per second when the bullet leaves the barrel.

How far has the slide moved when the bullet leaves the barrel?

Again we use the basic motion equation. Now that we know the acceleration and time, we can find the distance the slide moves:

Xf = Xi + Vi x T + (A x T**2) / 2

Xf = 0 + 0 x .001 + (13695 x .001**2) / 2

Xf = .0068475 feet = .082 inches, or just over 80 thousands of an inch.

You’ll find that with your 1911 slide .082 inches retracted, the barrel and slide will still be locked together. John Browning did all the stuff I did above over 100 years ago (once smokeless powder was invented so everything didn't get gummed up) when he started designing machine guns and semi-automatic pistols.

Recap:

Bullet velocity at barrel exit: 830 fps
Time bullet is in barrel: .001 second
Bullet acceleration while in barrel: 830,000 fps**2, or just over 25,000 G’s.
Slide acceleration while bullet is in barrel: 13,695 fps**2 or just over 425 G's
Slide velocity when bullet exits: 13.7 fps
Distance barrel/slide moves while bullet is in it: .082 inches

Note: The slide is accelerated ONLY while the bullet is in the barrel, so it’s only accelerated for .001 seconds. That’s why GLOOB kept trying to tell you that you couldn’t possibly apply over 850 pounds of force to the barrel to accelerate the slide as fast as the bullet does. You can see where the recoil spring force (16 or 18 pounds or so) is pretty irrelevent while the bullet is accelerating.

Notice that NOWHERE above does bullet/barrel friction come into play. If your 1911 has 10 pounds of barrel friction and a 230 grain bullet exits at 830 fps, it will experience the forces and timing above. If it has 1,000,000 pounds of barrel friction and a 230 grain bullet exits at 830 feet per second, it will also experience the exact same forces and timing above. Chamber pressure will have to be higher and your barrel and slide better be a LOT stronger, but the massive bullet drag will have NO effect on recoil, slide velocity, or slide position because it’s an internal force.

All of the stuff above is freshman year engineering Calculus 1, Physics, and Statics. No way anyone is going to explain it on an internet forum to anyone who does not have the fundamental background to understand it. I can see where it aggravates some people who understand trying to explain it!

Since we know the slide velocity, slide mass, barrel mass, recoil spring rate, and location where the slide unlocks, we could go on to calculate the slide velocity when it unlocks, the barrel velocity when it hits it's hard stop, the slide velocity when it hits it's hard stop in recoil, the time it takes to reach full recoil, and how long it will take to return to battery. We ignored the contribution of the recoil spring, hammer spring, unburnt powder, and gases exiting the barrel. Feel free to add them into the calculations if you feel the need.

 

[Walt Sherrill]

Actually, the forces and momentum are EXACTLY equal.

I worded my original comments, to which you responded above, inelegantly. The forces applied are EXACTLY equal, but the amount of movement of the different components is different because the components being moved are not the same/equal -- which is why I said the bullet moved quickly and the rest of the components moved more slowly. I'm not sure your comments (and inserts) otherwise addressed the issue that was the focus of this part of the discussion. I admit that my understanding of physics isn't what I'd like it to be, but that may or may not be the problem here.

I understand and can explain barrel rise in a revolver. That's because the barrel is directly connected to the frame. Recoil force is directly applied to the barrel's long "handle"/grip. Then, (I hope I'm using the term correctly), that rearward movement caused by recoil becomes a vector force, which causes the barrel to tilt because the grip position is fixed and immediately at play. If the barrel could somehow be centered on the grip there might not be any barrel rise.

As I understand it -- perhaps wrongly-- in a Browning Short-Recoil Locked-Breech gun, the relationship of bullet travel to slide and barrel travel is always the same for a given gun. If the bullet moves faster down the barrel, the barrel and slide move faster in the other direction; if the bullet moves slower, the barrel and slide move slower. It's a fixed physical relationship. Different recoil springs, buffers, and loads can change the timing of that movement, but not the relative positions of the barrel, slide, and bullet as they do their job. What happens BEFORE the bullet leaves the barrel is the focus.

With a Browning SRLB gun, the bullet leaves the barrel by the time the slide and barrel have moved only a fraction of an inch to the rear -- roughly 1/10th of an inch with a .45. Once that bullet is gone, the barrel and slide continue on their path. A hotter load or heavier bullet does not cause the physical relationship between bullet travel and slide/barrel movement to change. If the barrel and slide have moved only 1/10th of an inch before the bullet has left the barrel -- regardless of bullet weight or velocity -- what force is causing the barrel to rise more with a heavier, slower bullet than with a lighter, faster bullet? And how is that force applied to cause barrel rise?

Does your understanding of physics offer an answer?

It would appear that the folks making the high speed videos chose exactly the right loads for their video sessions so that there was no obvious barrel rise when they made their videos. And all of the different videographers did it just right. When I did my own very psuedo-scientific testing, I did not see different points of impacts when using different weight bullets on targets set at 30'. I didn't change my sights or point of aim and I shot the different weight rounds intermixed from the same magazine, using a rest.

Perhaps I'm I just the victim of trick photography (or particularly astute videographers) and have fooled myself by my own poor testing techniques. If so, can you, with your (better than my) understanding of physics, explain this apparent lack of barrel rise?

 

[ShootistPRS]

Thank you, 45_Auto, for relieving me of having to type in that four pages of explanations. Taking the end product of .082" of movement while the bullet is in the bore Makes it easy to understand why you don't "see" the movement on high speed photography. If the muzzle rises just .010" in the 8 or so inches between the hand and the muzzle at 25 yards the bullet hits 1.125" higher than the actual line of the bore before the trigger was pulled.
When you change the weight of the bullet and slow it down it spends more time in the barrel which can raise the muzzle more. (larger bullets usually carry more momentum than lighter bullets in spite of the lower velocity)

 

[Walt Sherrill]

Thank you, 45_Auto, for relieving me of having to type in that four pages of explanations. Taking the end product of .082" of movement while the bullet is in the bore Makes it easy to understand why you don't "see" the movement on high speed photography. If the muzzle rises just .010" in the 8 or so inches between the hand and the muzzle at 25 yards the bullet hits 1.125" higher than the actual line of the bore before the trigger was pulled.
When you change the weight of the bullet and slow it down it spends more time in the barrel which can raise the muzzle more. (larger bullets usually carry more momentum than lighter bullets in spite of the lower velocity)

I read the part you were addressing. I read that to be an explanation of how to calculate slide and barrel movement to the rear, not how much the barrel has risen as (or right before) the bullet leaves the barrel.

You continue to assume barrel rise you but you haven't shown us WHY the barrel rises or identified the forces that make it happen.

Bullet velocity at barrel exit: 830 fps
Time bullet is in barrel: .001 second
Bullet acceleration while in barrel: 830,000 fps**2, or just over 25,000 G’s.
Slide acceleration while bullet is in barrel: 13,695 fps**2 or just over 425 G's
Slide velocity when bullet exits: 13.7 fps
Distance barrel/slide moves while bullet is in it: .082 inches​

Jim Watson also noted that his 200 gr. and 230 gr. .45 rounds grouped together. By your reasoning that ought NOT be the case. Jim also wrote that his 185 gr. rounds hit lower, and he didn't understand.

JohnKsa said that the 185gr. round's lower point of impact was due to the 1911's barrel link in Jim's gun, which was not optimized for the 185 gr. round. (I didn't realize that a link could play that big a role in barrel positioning when the slide had moved only .082 inches, but I continue to learn about 1911s.)

If JohnKsa is correct, that difference has to do with how the barrel and slide interconnect in the 1911 -- their physical relationship which is controlled by the barrel link (and which is less than optimal in Jim's gun when shooting the 185 gr. rounds.) Apparently linkless systems work without that complication.

I'm still looking for an explanation of why a heavier, slower bullet causes the barrel to rise BEFORE the bullet leaves the barrel in the Browning SRLB design. Maybe it's there to be seen, and I just can't see it. (It won't be the first time that has happened.) Somebody on this forum generally comes through with an explanation I can understand, and when he or she does on this topic, showing me the error of my thinking, I'll be grateful and will have learned something of value.

 

[AxlMyk]

Stopped by my local gun shop to buy the ammo and was talking with the owner about my problem. He whips out a 3913 from under his shirt and proceeds to tell me

He un-holstered his loaded weapon right there? Is he stupid, ignorant, arrogant, or all 3?

 

[ShootistPRS]

Walt,
Are you a good enough shot to separate two groups that are a half inch apart or would it look like one group at 25 or 50 yards?

If the barrel of the gun moves .082" it is reasonable the the back end of that gun moves .010"?

You have already said you have good enough eyes to to tell the the gun is not moving AT ALL in the slo-mo videos.

The link in 1911s are all the same. Having a different bullet has nothing to do with the link. "Linkless systems" use a ramp to replace the link. It is cheaper to mill a ramp than it is to make the link. With or without the link the barrel tilts down at the rear (up at the front) before the barrel disengages with the slide.

You are never likely to see the angular change in a semi-auto handgun as it is being fired. Human eyes are not that good. Fire your handgun at a longer distance and the change in point of impact will be more visible.

 

[Walt Sherrill]

If the barrel of the gun moves .082" it is reasonable the the back end of that gun moves .010"?

If the FRONT of the slide moves .082" inches to the rear, the REAR of the slide will also move .082" to the rear. It's not easy to calculate how far the frame itself will move to the rear due to slide movement, because the slide and barrel are only indirectly connected to the frame at that point in the firing cycle. (As the bullet is about the exit the barrel, slide movement has just started to lightly compress the recoil spring and will only compress it for a that 1/10th of an inch of slide movement before the bullet is gone.) Spring compression will continue, but the bullet is gone so what happens from that point on can not affect the bullet's path.

Before the bullet leaves, the frame is receiving some of the force applied to the recoil spring, but its not immediately obvious how much force is being shifted to the frame. We also don't know how much the front of the barrel, slide and frame will tilt/rise as a result of the barrel and slide's .082 rearward movement, or the frame's .01" rearward (and downward) movement -- if it moves that much, or more.

Can you tell us how you came up with your .01" figure? Did you find a calculation that led you to that result? As I read what you wrote, it seemed more like a "SWAG" figure used to explain how rounds hit a target down range that gave you a way to "back into" a barrel rise calculation. You say .01" is a reasonable assumption. If so, how does that very small frame movement lead to barrel rise? Is the whole frame assembly (including the grip) moving to the rear, or is the grip twisting in the shooter's hand, allowing the barrel to rise while the rear of the frame dips? If the top of the slide is pushing back against the frame we may be talking about a vector force, and there may be a way to calculate it. How do we calculate that force and its effect?

Your claim that a slow-moving heavy bullet will cause more barrel rise in a SRLB semi than a fast-moving light bullet may be correct, but that claim is offered without evidence and with only theoretical justification. You also say that high speed videos are not precise enough enough to show the subtle rise that occurs when heavy, slow-moving bullets are fired. Perhaps, but I'd argue the videos are better evidence than no evidence at all.

Maybe someone else here can give us better explanations and put us (or me) out of our misery.

 

[lwestatbus]

Its Not the Gun--Its All Me

Well THIS is embarrassing after the doctoral dissertations in physics and the extensive exchanges. It turns out the gun shoots where it is pointed but I don't seem to point (this gun) very well.

As promised, I bought a box of 124 gr and one of 147 gr cartridges and headed to the range. The 124s were shooting right where the 115s were, about 4" low at 20 ft. The 147s were slightly higher but if I were assigning this as a problem to my graduate statistics students I think they would tell me that any difference in the center of the group could not be considered significant due to the dispersion of the two groups (ouch). Regardless, all three cartridges were shooting low.

This range isn't really well set up for bench shooting but I was getting frustrated and worked with the range master to shoot supported from the firing point's table. I had to rest the pistol on the magazine to keep the rounds in the impact area (I know, not preferable, but still better than unsupported).

From the rest I was able to put a full magazine each of all three cartridges into tight groups right at the point of aim (bottom of a 2" Shoot 'n See paster).

Sigh. So that means the issue is with me and the pistol. I shoot multiple other pistols quite competently so I have some learning to do. The 3913 trigger is much heavier than my others so that may take getting used to. After the bench shooting I experimented with some different finger positions on the trigger but nothing conclusive came out of that. I also have the darndest time on just this pistol with focusing on the sights. I get a lot of ghosting on the top edges of both front and rear sights so it may be that I am just not aligning the sights correctly. That is my current front runner theory as I have been able to achieve some acceptable but low groups shooting free hand.

The bottom line is that the pistol definitely shoots well enough for defensive use in a pinch and I would most likely doing point and shoot with it anyway. I may get hits in the gizzard when I was aiming at the 10-ring but enough of them should put someone down regardless. But I also want things to work the way they are supposed to and this is the kind of problem that wears at my craw until I solve it.

Many thanks for all of the responses and activity in the thread. I definitely learned some things about firearm engineering.

AxlMyk: He un-holstered his loaded weapon right there? Is he stupid, ignorant, arrogant, or all 3?

None. I didn't have any problem with his conduct. It was safe in all respects. When I said "whipped out" that was hyperbole. The shop owner then went to the back of the store and came out with a second unloaded 3913 which he proceeded to dissect in considerable detail. It was quite educational, just like this thread has been.

 

[Walt Sherrill]

The 3913 trigger is much heavier than my others so that may take getting used to.

A slightly lighter hammer spring, which you might be able to change yourself, could make a world of difference in that HEAVIER trigger.

 

[DaleA]

Good on you lwestatbus. Now when anybody talks about 115, 124, 147 grain rounds you'll be able to say I know how the gun shoots with those, I've actually done it.

Shooting a gun from a rest or a supported position is something I always try to do with a new gun as soon as possible. I get to see just how tight a group the gun is capable of and then that shames me when I practice and spurs me to try harder and practice more.

It's all fun!

Good luck and stay safe.

 

[JohnKSa]

Taking the end product of .082" of movement while the bullet is in the bore Makes it easy to understand why you don't "see" the movement on high speed photography. If the muzzle rises just .010" in the 8 or so inches between the hand and the muzzle at 25 yards the bullet hits 1.125" higher than the actual line of the bore before the trigger was pulled.
When you change the weight of the bullet and slow it down it spends more time in the barrel which can raise the muzzle more.

All this ignores the fact that you can look at the bore line and sight line and tell if the muzzle rises significantly while the bullet is in the bore or not.

If the muzzle rises significantly between the time the trigger is pulled and the bullet leaves the bore then the muzzle will be pointed down in relation to the sight line.

Since it can be clearly seen in the figure I posted that the bore actually points upward relative to the sightline of the autopistols I checked, there's no need to theorize about whether the muzzle rises significantly or not. The measurement shows it doesn't--at least in those pistols.

On the other hand, it clearly does rise significantly in the revolver I measured.

 

[pete2]

My experience---------------
92FS, had to install higher rear sight
Kimber 1911 45, filed front sight
Ruger CMD 45, filed front sight
Citadel 1911, 9MM, filed front sight.

It doesn't matter a lot, if any, what weight bullet you use in a semi auto.
Ruger told me they don't care where a gun shoots as long as it groups(the wouldn't do anything about the problem) they did put a black sight on it so I could file it down, they replaced the first gun due to a mis machined frame(I returned it because it shot low). Beretta also blew me off when I called them.

Bottom line, replace the sights or file the front. A worse problem is if it shoots high.

 

[45_auto]

Perhaps I'm I just the victim of trick photography (or particularly astute videographers) and have fooled myself by my own poor testing techniques. If so, can you, with your (better than my) understanding of physics, explain this apparent lack of barrel rise?

I'm not really sure what you're looking for. Post below is a reply to one of your previous threads on the same subject a couple of years ago.

It should be obvious by the difference between the Point Of Aim (POA) and the barrel axis on a semi vs a revolver.

Front and rear sights on a semi auto are typically almost the same height, which means that the POA is very close to the barrel axis. However, the front sight on a revolver (or fixed barrel like a Contender pistol) of any power will be SIGNIFICANTLY taller than the rear sight. Therefore the barrel axis on a revolver intersects the target MUCH lower than the barrel axis of the semiauto.

What other conclusion can you draw other than semi-autos have reduced or delayed barrel rise during the time that the bullet is in the barrel?

(The difference is that the semi is primarily conserving momentum as linear momentum by using the slide/barrel to compress the recoil spring and hammer spring while the bullet is in the barrel. That momentum is then transferred to the frame and shooter's hand, at which time a significant portion of it is conserved as angular momentum, resulting in barrel rise. Since a revolver has no moving parts with mass to initially conserve the bullet's momentum, the momentum is conserved by the rearward movement of the barrel/frame being turned into angular momentum by the shooters wrist joint while the bullet is in the barrel.)

That's about the simplest way I can think of to put it. A heavier bullet imparts more momentum to the slide/barrel. That momentum is transferred to the shooters grip/wrist through the hammer/striker/recoil spring while the bullet is in the barrel and the slide/barrel starts moving rearward. The linear momentum of the slide is reacted as a torque through the shooter's wrist. Heavier bullet = more momentum = more torque on shooter's wrist.

Whether that additional torque due to the heavier bullet is enough to affect your group would seem to me to be dependent upon the magnitude of the forces, the strength of your grip, and the height of the bore axis.

I've never really cared enough to do any research on it, if you really want to know how much a 9mm bullet weight can affect POI, it seems it would be easy enough to quantify using something like a Ransom Rest to provide a repeatable resistance to the torque and a series of different bullet weights as your variable.

 

[Walt Sherrill]

That's about the simplest way I can think of to put it. A heavier bullet imparts more momentum to the slide/barrel. That momentum is transferred to the shooters grip/wrist through the hammer/striker/recoil spring while the bullet is in the barrel and the slide/barrel starts moving rearward. The linear momentum of the slide is reacted as a torque through the shooter's wrist. Heavier bullet = more momentum = more torque on shooter's wrist.

That is a simple way to explain things, but you keep repeating your theoretical understanding of how things work, and you don't offer us any proof that Browning short-recoil locked-breech guns behave that way. Some evidence would make your argument more convincing.

Until the "extra" momentum (of the heavier, slower bullet in teh barrel) in the slide/barrel is passed to frame, it arguably has no effect. Your simple explanation ignores the fact that with a BROWNING SHORT-RECOIL LOCKED-BREECH SEMI-AUTO the relationship of the bullet to the slide and barrel, and the slide and barrel's relationship to the frame IS A FIXED, MECHANICAL/PHYSICAL RELATIONSHIP. That relationship -- how far the the different components move with regard to each other, not how quickly they move -- stays the same regardless of bullet weight or bullet speed.

The only thing really varies with bullet weight and velocity with the Browning SRLB design, is the time it takes for a bullet and barrel/slide to move. The slide will move just as far when a heavy bullet is fired when the bullet leaves the barrel as when a light one is fired. The slide and barrel may move more slowly or more quickly, but the physical distance traveled is based on the physical relationship of the components at any point during the bullet's travel, and it's a fixed, physical relationship until the bullet leaves the barrel.

IF the slide travels the same distance regardless of bullet weight or speed when the bullet leaves the barrel, where is that extra force necessary to make the barrel rise seen and how is it transferred to the frame? Doesn't slide movement drive everything that follows? And how is the extra force that accompanies a heavier, slower bullet transferred to the frame BEFORE the bullet exits the barrel? It has to be done before the bullets exits to have any effect. What makes the barrel rise before BEFORE the slide has begun to move to the rear? That extra force can't come into play until the slide starts to move because there's no real connection (or way to transfer the force in quesiton) to the frame until it does move.

There is only an indirect connection between the barrel/slide and the frame until AFTER the bullet has left the frame and the barrel and slide hit their frame stops. The recoil spring will be only slight compressed by that by initial 1/10th of an inch of slide movement because the spring is not solid. More importantly, only PART of the force at play can be transferred to the frame in that early slide movement, because part of the force passed to (and through) the spring will be stored in the spring for later use. And even then, the force that is transferred is transferred against the frame at a lower point on the frame and that would suggest that the effect of that force transferred to the frame as a vector force is reduced.

High speed videos do not show slide/barrel rise before the slide begins to move. It doesn't appear visible as the slide begins to move. It also doesn't show barrel rise until AFTER the bullet has exited,

Jim Watson says his 200 gr. .45 rounds group with his 230 gr. .45 rounds. Only his 185 gr. .45 rounds hit lower. JohnKsa says that lower impact could be attributed to a barrel link issue. I would expect a 230 gr. .45 bullet that was 15% heavier than a 200 gr. bullet to have a different point of impact if what you say is true.

When I tried the same sort of test using one of my 9mm semi-autos, using a linkless barrel, I found that my 115, 124, and 147 gr. 9mm bullets all grouped about the same, even though the heaviest bullet was 28% heavier than the lightest.

lwestatbus, whose post started this discussion, and someone who is professionally very comfortable dealing with data sampling and statistics, says that any statistical differences in the center of the groups he fired using different bullet weights could not be considered significant.

Your rationale, above, clearly applies to how a fixed-barrel gun works, but may not be a good explanation for Browning design behavior. It seems that the bulk of the recoil from the Browning design doesn't get applied to the frame until AFTER the bullet has left the barrel. While some recoil force does get applied to the frame before the bullet is gone, it does so only indirectly as explained above, through the limber recoil spring -- which is hardly a great transfer medium. That "pre-bullet exit" force appears to have a very minor effect on barrel rise in the Browning design.

What force is at play that causes the barrel to rise as you say it must. And how do you measure (or demonstrate) it, to show that your claim is valid? Slide movement (how much, how far) seems to be the same regardless of bullet weight or bullet velocity until the bullet is gone.

Shots from a single gun in a Ransom Rest,with the sights reset on the point of aim (but not adjusted for the different bullet weights) to the same point of aim with each shot might convince most of us. Loading the different weight bullets in the same magazine (by a different person), so that not even the shooter knows what's coming with each shot, might add more credibility to the results. The mag loader will have to record the bullet weights for later evaluation.

(While I used a sandbag rest rather than a Ransom Rest, that's a bit like the approach I used with my own 9mm test, but it might have worked better if I had used ONE target, and numbered the shots on the target after it hit, so the bullet weight of each shot could be identified, later. I may try that if I do additional tests.)

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[lwestatbus]

Does Shooting From a Rest Make a Difference

The bore-line vs. sight-line and muzzle rise due to recoil, shooter behavior, or the Will of Thor have become front and center in this thread.

I am still left with a decision about what to do about my connection with this pistol. I have four facts that bear on my decision:

1. Pistol Shoots Low Firing Unsupported: When firing this pistol with a 2-handed grip unsupported I shoot about 4" low at 20 feet. The groups are acceptable if I pay close attention and are definitely groups. This has been consistent through a few hundred rounds now and three different bullet weights (115, 124, 147).
2. Pistol Shoots Right on Point of Aim Firing Supported: 'Nuff said
3. I Have No Trouble With Other Pistols: I regularly shoot multiple other pistols and do NOT have this low grouping with any of the others. The other pistols include Kimber Pro Carry .45 w/ 4" barrel and fixed sights, PPK/S, Kimber Micro 9 w fixed sights, S&W Model 60s with 3" and 5" barrels.
4. The Sights on JUST This Pistol Are Fuzzy to Me: I've mentioned elsewhere that on just this pistol I get ghosting of both the front and rear sights where, if I concentrate, I can make out two distinct edges for each. One is hazy and one is blacker but the overall effect is blurry. I freshened up the white dots in the sights with an oil based paint pen and this helps.

All of this leads me to two questions:

1. Will shooting from a rest affect any designed 'flip' of the gun while the bullet is still in the barrel?
2. What should I do next?

 

[Walt Sherrill]

... what should I do next?

1. Consider going to (or joining) the S&W forum. Lots of very helpful (and VERY knowledgeable) folks there, and there's an existing topic where participants give recommendations for upgrading the sights for the 3913. I visited there a lot in years past when I had some 3rd Gen S&Ws, and still visit (because I have an M&P Pro. The following is just a link to one area... it a much broader site than that.

http://smith-wessonforum.com/smith-wesson-semi-auto-pistols/

Many of us believe that any flip mostly occurs AFTER the bullet is gone, so that shouldn't affect where the bullet goes.

2, See if you (or your gunsmith) can change to a slightly lighter hammer spring.

3. Re-evaluate the gun, shooting from a rest (see POOR-MAN'S REST and BULLSEYE WHEEL OF MISFORTUNE TOOL, below)

4. Get new sights that are more "eye"-friendly. The link above should help with that, and then go to Amazon or EBAY for a good price.

5. If you don't have one, consider getting a reasonably-priced generic sight pusher from the same place... as you'll use it many times over the coming years. You can find good ones for way under $100.)

POOR-MAN'S REST

About the shooting rest: The ideal inexpensive rest for most folks is a bag of rice (not the smallest bag), carried and used inside two plastic bags in case of a break or tear.

Rest your hands (holding the gun). not the gun, on the bag, and very slowly press the trigger. That reduces the "human factor" to a minimum.

Doing this CAN (not WILL) quickly show you whether an accuracy issue is the shooter or the gun.

Start evaluating the gun at about 15' and then move the target back once you start understanding how things are going.

NEW guns can be a challenge, particularly if they feel and fit you differently than other guns you're familiar with -- so some of your gun "issues" may resolve pretty quickly.

BULLSEYE WHEEL OF MISFORTUNE TOOL:

For unsupported shooting, use the Bullseye tools (link below) to examine your results.

While this tool is intended for one-handed fire, most folks don't use both hands properly when shooting, and their strong hand plays a bigger role in the process than they realize, and contributes more to the target results than you'd expect. It can still offer meaningful guidance.

A sight pusher might be helpful at the range. A brass punch [or hardwood dowel] and light hammer will work, too. Move the rear sight in the direction you want the point of impact to move to. If the front sight can be moved, and you choose to move it, you move it in the opposite direction. You may not be able to do anything about elevation without changing the sights (but you want to do that.)

Here's a link to the Bullseye tool. It tells you how to evaluate what you see on the target. (If you're left-handed, you "mirror-flip" the chart.)

http://www.bullseyepistol.com/training.htm

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[random guy]

Wasn't sure what to think about this. From experience, heavier bullets and slower velocity means a higher POI in handguns, but upon reflection, most of my shooting has been with fixed barrel guns and linked barrel semi autos.

I also thought that loads fired from magnum revolvers can vary far more than in semi autos so I picked two of the most extreme 9mm loads to test. 95gr Sierra was the lightest 9mm bullet on hand and 147gr XTP being the top end. I loaded the 95 to max velocity (1356fps book) and the 147 to the starting charge (857fps book). Both using Longshot powder. Not really ideal for the light load but good enough to see what I assumed would be a major elevation shift. But I didn't really see it.

I fired 5 rounds each at 12.5 yards with the first round slingshot loaded in each group. Pardon the 147gr group (I'm going to blame an inappropriate powder for the scatter) but if you look at the group centers, there is little vertical movement. Even doubling the change at 25 yards wouldn't amount to more than 2" if that. Maybe an inch would be closer.

http://s107.photobucket.com/user/hvap90/media/Shooting/POI test 95 vs 147 gr.jpg.html

Some floating barrel semi autos may behave differently but this one (S&W M&P 9) defied my preconceptions. On the bright side, this indicates that these pistols tend to shoot most loads to virtually the same POI...a very nice thing.

 

[JohnKSa]

Nice test.

I've got three boxes of 9mm ammo, all from the same manufacturer and all with different bullet weights that are slated for a test like yours.

I'm going to add one wrinkle. In addition to shooting groups from all three weights to see if a POI difference can be seen, I'm going to fix the slide closed and fire the groups again with all three weights. Right now the test is on hold while I come up with a reliable and practical way to fix the slide closed without causing any damage to the pistol.

I know it's possible to hold the slide closed with one's thumb (I've done it) but that will alter how the pistol is held so I don't want to do it that way. I'm thinking that I may have to do something like ziptie the slide closed (large ziptie looped around the back of the slide and front of the triggerguard) for each shot then cut the ziptie off to manually chamber the next round and repeat.

 

[ShootistPRS]

I fired 5 rounds each at 12.5 yards with the first round slingshot loaded in each group. Pardon the 147gr group (I'm going to blame an inappropriate powder for the scatter) but if you look at the group centers, there is little vertical movement. Even doubling the change at 25 yards wouldn't amount to more than 2" if that. Maybe an inch would be closer.

Fire the same loads from a rest at 25 and 50 yards. At those ranges the difference will show up a lot more.