How do bullet weights and velocity affect point of impact?

[crghss]

OK, one last time.....and I'm out.

Here you go...key word gas dissipation.

http://www.magnaport.com/hgun.html

the primary focus of gas dissipation helps reduce the muzzle lift.

Mag-na-port offers a unique system of porting semi-automatics by using a trapezoidal port through the barrel and an oversized expansion vent through the slide to allow maximum dissipation without fouling.

As for your sailing idea thats gibberish. If your correct then people could never sail downwind (wind to your back)....where are they redirecting the wind to?

the Bernoulli Principle/Equal-Transit-Time theory and the Newtonian theory

Doesn't matter which theory you subscribe to they both go with the premise that there is more PRESSURE on one side of the wing/mast then the other.

Here is a link to help you better understand. (hate to Wikipedia bit the illustrations help provide an understanding)

http://en.wikipedia.org/wiki/Lift_(force)

And here is another link.....what are airfoils?

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

Sails are airfoils that work by using an airflow set up by the wind and the motion of the boat. The combination of the two is the apparent wind, which is the relative velocity of the wind relative to the boat's motion. The sails generate lift using the air that flows around them.

Thats it...I'm done.....should I walk to the pier and go fishing or the beach and go kitesurfing?????? Hhmmm

 

[robhof]

robhof

Veral Smith of LBT technology, has an article in his book about mid-barrel porting and how it reduces felt recoil and actual noise. He apparently has done extensive research on this, but many find a gun with tiney holes mid-barrel not to their liking. Aesthetics wins over on practicality on many occasions.

 

[kle]

the primary focus of gas dissipation helps reduce the muzzle lift.

Yes, but what in direction are they dissipating the gas? Again, why not straight down (out of the shooter's line of sight, which would be useful) or off to the sides?

Doesn't matter which theory you subscribe to they both go with the premise that there is more PRESSURE on one side of the wing/mast then the other.

Okay, so how is this pressure generated?

Edit: Interestingly, the Wikipedia article says that the Bernoulli Principle is a derivation of Newton's 2nd Law of Motion, and that both downwash and pressure differences explain lift. So we're both right, or both not completely wrong.

As for your sailing idea thats gibberish. If your correct then people could never sail downwind (wind to your back)....where are they redirecting the wind to?

They'd do what sailors did for centuries before the triangular sail--they'd turn the sails perpendicular to the wind's direction and use the direct pushing effect. With the triangular sail, with the wind coming from the rear, they'd use the sail to push the boat along. With the wind coming from any other direction (except dead-ahead) they'd use the sail like a wing.

Thats it...I'm done.....should I walk to the pier and go fishing or the beach and go kitesurfing?????? Hhmmm

Knock yourself out.

 

[Uncle Billy]

Watch the video JohnKSa posted:

http://www.youtube.com/watch?v=kq-xcqs5NIk

... especially just after 1:14 when the gun is fired with no constraints to its upward motion in recoil. It seems clear to me that the recoil has three phases:

1) Just after ignition, when the bullet is moving down the bore and the slide has begun to move rearward: the only forces on the gun are the friction of the bullet moving in the barrel pulling the gun forward, the friction of the slide moving rearward, pulling the gun rearward, and the rearward force of the recoil spring being compressed. At 900 ft/sec muzzle velocity and a 4" barrel, this combination of forces lasts for about 0.73 milliseconds, and it's only during this time that any recoil effects can alter the bullet path. It's real short, but watch the trigger guard resting on the rest's peg without the rod holding it there and you'll see there is little or no motion until the bullet has left the muzzle. Revolvers don't have this tiny window of time since the entire gun feels all the recoil energy immediately (there's no mechanical action to absorb any), and though it's reduced by the barrel-cylinder gap a little (some of the gasses that escape that slot push against the frame both upward and downward which probably more or less cancels their vertical effect), it doesn't affect the gun's POA. But the slam of the case against the frame at the rear of the cylinder sure does, which occurs at the moment of ignition and is why the front sights are higher on revolvers that on autos- to help point the gun at the POA before the bullet escapes. I haven't measured this, but I'd bet the front sight on a long barreled revolver is higher than on a short barreled one, since the bullet is in a long barrel for more time than in a short one, allowing the recoil more time to affect its path.

2) After the bullet clears the barrel, and so is free of any recoil effects. The only forces on the gun then are the friction of the slide moving rearward and the rearward force of the recoil spring being compressed, which isn't subtracted from by the bullet friction any longer (bullet friction is hugely greater than slide friction- try to push a bullet down a barrel by hand, and see how much more force that takes than racking the slide). Watch the trigger guard lift a little off the peg it was resting on while the slide is moving rearward, after the bullet is gone. If you wish to feel how much force is involved, pull the slide back all the way- that's the force on the gun at this stage.

3) When the slide hits the rearward limit of its travel, transferring its momentum to the frame of the gun. This is the instant when the leftover recoil is shared by the entire gun and whatever is holding it. Watch when the slide hits the rearward end of its travel- the trigger guard leaves the peg and the whole gun and shooter's hand are obviously reacting to recoil, reduced a little as the recoil spring unloads, sending the slide forward.

Heavier bullets, with muzzle velocities equal to that of lighter bullets, must have larger forces behind them to attain that velocity, which will load the recoil spring faster and impart more frictional force from the slide's motion after they're fired and before the bullet clears the muzzle because the slide is going faster and has gotten more rearward in its travel (more spring compression) than with lighter bullets at the same muzzle velocity, which require less force to go that fast (the friction of the bullet in the barrel is due to what it's made of and its diameter, but not its mass).

 

[Dubs]

There seems to be two discussions going on here: Revolvers and semi-autos. I am going to repeat some things here.

First of all, the recoil effect of a bullet is immediate. The pressure from the powder exerts an equal force in every direction in the chamber (up and down cancels).

Secondly, recoil does not cause muzzle flip. Not directly. It only causes the gun to move backwards. Your hands cause the muzzle flip because they act as a fulcrum and the gun acts as a lever. If you used some mechanism to brace something directly behind the barrel (such as your shoulder on a long gun), there is no muzzle flip. That is why rifles are only ported on all sides.

Revolvers will being to flip immediately because the entire gun feels the effect of recoil the moment it is fired.

Semi-auto muzzle flip is significantly negligible because (a) the barrel is closer to your hand and (b) the slide absorbs most of the backwards force until the slide locks back completely. The slide locks back long after the bullet leaves the muzzle. The only lever action occurs from the friction from the slide to the frame.

All else being equal, faster bullets will hit higher, yet in revolvers, faster bullets will also leave the muzzle sooner and shoot lower. I think it's safe to say muzzle flip in revolvers is a messy combination of combining barrel length, bullet mass, and the quantity of powder.

All else being equal (including velocity and bore diameter that is), lighter bullets will hit lower because the force of air friction will have a more significant effect, but lighter bullets are often faster... again you'd probably have to crunch the actual numbers.

 

[colt357]

recoil and bullet trajectory

I am not an engineer, and I am sure that most of the participants in this discussion are far better versed on these issues than I am. So I am going to throw out a thought on this that has been rolling around in my head for a while now.

Is it possible that one of the factors causing the the slower traveling handgun bullet (generally the heavier one) to have a higher POI at typical handgun ranges has less to do with the angle of the recoiling barrel at the time the bullet leaves it, and more to do with the rate of accelleration of the recoiling barrell in an upward direction while the bullet is still traveling through it?

Kind of similar to traveling in a vehicle and shooting at an object on the side of the road when the sights are aligned to the target at about a 30 degree angle to the vehicle's line of travel. The target may have been in the line of sight at the time the trigger was pulled, and may still have been in the sight line when the bullet left the barrel. However, by the time the bullet traveled sufficient distance to where it should have impacted the target it missed because it was traveling along the original line of the vehicle's travel simultaneously traveling down it's own original sight line.

Just some thoughts on the effect on POI of the upward velocity of a barrel under recoil while the bullet is traversing it, versus the actual angle of the barrel at the time the bullet leaves it.

So far I have found this thread to be very informative and interesting.

I'll go back into lurker mode now and and look forward to learning even more.

Dennis

 

[Uncle Billy]

The upward acceleration of the barrel is not imparted to the bullet once the bullet is free of the muzzle. Its upward velocity is, however, and whatever it had at the instant the bullet clears the bore is added to the bullet's velocity. There can be no acceleration (CHANGE in velocity) unless there's a net force acting and once free the only forces on the bullet are the air drag it meets (which slows it down) and the downward pull of gravity (which also may affect how fast it's going, and bends its path toward the earth).

In a semi auto, the only upward motion of the barrel (recoil) that affects the bullet comes from the net difference between the friction of the bullet in the bore pulling the gun forward, and the friction of the slide and compressing of the recoil spring pushing it backward. Until the bullet is free of the muzzle, these are the only forces acting on the gun that result from firing a round that can move the POA; this situation lasts less than one one thousandth of a second if the barrel is 4" long and the muzzle velocity is 900 ft/sec. Since the line of action of these forces is above the location of the gun's support (the hand grip), the gun will rotate (recoil). The bullet is long gone by the time the slide reaches the rearward limit of its travel; when that happens, whatever momentum the slide has is instantly shared with the entire gun, which then leaps upward. Watch that video at about 1:14 and see all this go on. It's only the time it takes for the bullet to leave the barrel that recoil forces which alter the POA are present.

The slide forces are larger than the bullet friction so the muzzle rises. How much it rises depends on how far the slide has gone (i.e. how much the recoil spring is compressed) before the bullet clears the muzzle- the further back the slide is, the more the recoil spring is compressed which puts more recoil force on the frame and so rotates the gun more, altering the POA more. How far the slide gets before the bullet is free of the barrel depends on the force applied to it, and how long that force is present.

It's a complicated interaction: a heavier bullet loaded to achieve the same muzzle velocity as a lighter one will result in the bullets being in the bore for the same amount of time. But imparting enough force to achieve that velocity on a heavier bullet requires more force (heavier powder load). So even though the heavier bullet is in the bore for the same amount of time as the lighter one, the force is necessarily greater on it and so on the slide, which compresses the recoil spring more than the lighter load will in the same time, and makes the muzzle rise- the heavier bullet hits above the lighter one.

If one reduces the load behind a heavier bullet, the force on the bullet and so on the slide will be less. But the bullet will be going slower, taking more time to clear the barrel, so even though the force is less, it's applied for longer which moves the slide further before the bullet is clear, which loads the recoil spring more which raises the muzzle. What all this does to the POI I wouldn't want to predict. Lots of range time and a lotta reloads answers that one.

 

[tipoc]

With both revolvers and semis the muzzle rises in recoil. This is also true of rifles and carbines. Recoil moves directly backward but we don't. The force of the recoil causes our hands (or shoulders) to move back and slightly upward because with both wheelguns and semis the axis of the bore is above where we are holding the gun. This is shown clearly in pics and videos of guns. This is why we often speak of "getting the gun back on target" after firing a shot. Recoil pulls the muzzle of handguns upward. Less on semis than on revolvers but true for both.

Observe...

http://www.youtube.com/watch?v=G0VjdI_S_HM

http://www.youtube.com/watch?v=T8C5Mjh4l54&feature=related

http://www.youtube.com/watch?v=sb6nsrQkvXk&feature=related

With both wheelguns and semis the heavier bullet usually hits higher than the lighter, faster bullet.

Do not confuse compensators with porting or with flash suppressors. They are different and act differently. They do not eliminate recoil but by porting the hot gases upward they help to compensate for it's effects by forcing the barrel back down.

It is also clear from pics and videos that hot gasses are expelled before the bullet leaves the muzzle. This is the case because some of the gas, which travels faster than the bullet, escapes from around the bullet as it roams down the spiral tube.


tipoc

 

[crghss]

OK

"This is the case because some of the gas, which travels faster than the bullet"

WOW...please tell me, if what pushes the bullet down the barrel is the expansion/pressure of the gases then how can the gases be faster then the bullet? As fast as the gases travel then the bullet must also. Because the only thing pushing the bullet or impeding/restricting the expansion of the gases is each other.

 

[kle]

This is the case because some of the gas, which travels faster than the bullet, escapes from around the bullet as it roams down the spiral tube.

I'd say that that initial bit of gas is the gas that escaped before the bullet obturated enough to seal the bore and the gas behind it.

 

[rodfac]

Look at a cpl of hi speed videos crgss...you'll see that gas is exiting the muzzle before the bullet. No bullet produces a complete gas seal in the barrel. Rodfac

 

[crghss]

OK, if you say so....

 

[tipoc]

Yep some of the gas passes in front of the bullet before it has a chance to obdurate to the point that it blocks powder residue, etc. But it is also the case that, at times, obduration is not complete or perfect for the full length of the barrel, sometimes due to imperfections in the barrel or in the ammo, bullet type, etc. This latter provides for variations in accuracy and muzzle velocity among other things, particularly with jacketed ammo. The seal is not always perfect. This is why (one reason any way) that some guns are more accurate with some brands of ammo than other brands. But mostly it is the gas, and sometimes bits of residue, preceding the full obduration of the bullet. This is what you see in the videos. Old timers knew this and it is one reason for gas checks on some bullet designs by Elmer Keith and others.

Yeah the expanding gas moves faster than the bullet.

tipoc

 

[kle]

Old timers knew this and it is one reason for gas checks on some bullet designs by Elmer Keith and others.

I thought the reason for a gas-check was to prevent the bottom of the bullet from burning away from slow-burning powders, as a precursor to full metal jacketed bullets.

Invoking the almighty Wikipedia again, it seems you are correct. Interesting.

 

[JohnKSa]

After working through the math for a number of test cases and doing a number of comparisons it has become apparent that tipoc is exactly correct.

At 8 yards the difference between the point of aim and the point of impact of the 135 gr. versus the 200 gr. will be negligable, maybe an inch if that. But the felt recoil between the two will be quite a bit and in this case the difference in a 6" point of impact at 8 yards is due to the shooter. It is the shooter who is causing the lighter bullet to hit 6" higher than the heavier at 8 yards and not the gun or the load.

Out of the same gun I could not make the math work out to result in a light bullet hitting this much higher than a heavy bullet loading. In fact, I was unable to come up with any reasonable scenario in which a light bullet loading would hit higher on the target than a heavy bullet loading out of the same gun.

The POI difference in this situation can only be due to the shooter anticipating recoil (flinching).

I plan to do some research at the range next time I get a chance. I will attempt to quantify POI differences due to bullet weight differences and verify the accuracy of my mathematic simulation. So expect another update to this thread down the road.

 

[WESHOOT2]

observable handgun behavior

1) gases exit before bullets

2) heavier bullets tend to shoot higher due to recoil raising the muzzle


Now one may work on the physics of why.