Recoil and Semi-Autos (and maybe Revolvers, too)...

[Bongo Boy]

Almost 100% of it is,

Yes. You gotta separate the stuff you see and experience from the stuff that happens. JeffK's comments are the key to understanding what's happening. The gun and the shooter get hit with an extremely short impulse...and that impulse is basically over when the bullet leaves the bore. The gun and shooter have been smacked with a baseball bat, the bullet is down range, and everything else that happens is in response to that smack. The only forces acting on the gun the instant after the bullet leaves the muzzle are: 1) the shooter holding the gun, and 2) gravity.

The part that's kinda hard to comprehend in is that velocity is only how fast the gun is moving...regardless of the fact the gun has only moved 100 thousandths of an inch. It accelerates to a high velocity before it moves a perceptible amount, and very soon starts getting slowed down by bone an muscle. How soon? Well, think 'taking up slack'...the gun doesn't see much resistance to motion from the shooter until the shooter's body reacts either with muscle or with mass, and both. That takes time because the mass is a spongy connection (fat, skin, muscle, air), and muscle doesn't react very quickly at all (I'm thinking at least 100 ms).

 

[JohnKSa]

JohnKSa, as you can see, you're trying to quantify time differences involving hundredths of thousandths of seconds, distances involving thousandths of inches, and forces involving thousands of pounds. I'd be very surprised if your hold is repeatable enough to draw any valid conclusions without a machine rest.

It will be interesting to see the results, but you're right, the times involved are very small and the forces large. It may be that most of what's happening while the bullet is in the bore is tissue compression in the hand, not really any effect of the grip. If that's the case, altering the grip can only have a very small effect by trying to pre-compress the tissue. I figure it's worth trying it to see what happens.

 

[Walt Sherrill]

Is there any torque applied in the-semi-auto BEFORE the bullet leaves the barrel?

Almost 100% of it is, since by the time the bullet leaves the barrel the pressure behind it is small (ideally very small, since whatever is left is doing no good and is just creating more recoil, flash and bang - the reason .357 snubbies are such beasts to fire, even though the bullet doesn't wind up much faster than a .38 out of the same gun), and the only thing left to eject is gas and some powder. The whole recoil process is set off in that first millisecond, the torque and the backward force.

I don't doubt that recoil's effect is immediately at play with both a semi-auto and revolver. What I do question is whehter both weapons types are affected by that recoil in the same way.

With a revolver, the force immediately affects the frame: the barrel and frame are one unit, and the frame is a handle that is torqued. With a semi-auto, the force immediately affects the barrel/slide, but until AFTER the bullet has left the barrel, the slide and barrel do not fully engage the frame. There is clearly a small amount of recoil-induced force, early on that compresses the recoil spring, and that spring is based against the frame. That early interaction has to have some Torque effect. But unlike a revolver the frame isn't yet fully engaged in the effect of recoil.

This entire discussion has been focused around THAT point -- the consequences of the recoil-induced movement of the slide and barrel before they engage the frame -- and whether that movement plays a role in how the bore-axis it tilted by recoil.

What started this discussion in a different discussion chain was my statement that heavier bullets in a semi-auto hit higher -- a statement that was immediately called into question.

Do heavier rounds have higher points of impact because they cause MORE recoil-induced barrel rise in a semi-auto? I was told no. We've been talking, arguing, and exploring ever since.

All of the examples we've seen address valid points, and all of the discussions with formulas used to make points, generally deal with good examples, but none of them seem to directly address the question of a possible difference in whether the rearward (equal/opposite) action differs in the the two types of weapons. It seems to me they do. And that point might tells us that semi-autos behave differently than revolvers for reasons other than their lower bore-axis.

Locking the slide on a semi-auto MIGHT offer some evidence, and hopefully we'll get results from doing it both ways in a semi-auto, soon.

 

[David R]

The barrel and slide are locked together until pressure is low enough to unlock after the bullet leaves the barrel. How much pressure or rearward force is applied before the bullet leaves? I will try to shoot different weight bullets tonight from my 1911 45.

 

[Walt Sherrill]

The barrel and slide are locked together until pressure is low enough to unlock after the bullet leaves the barrel. How much pressure or rearward force is applied before the bullet leaves? I will try to shoot different weight bullets tonight from my 1911 45.

That could show that heavier bullets traveling more slowly do cause more tilt/rise to the bore-axis in a semi-auto -- as some claim and others deny. That would deal with one of the questions we're addressing. I would remind those reading that the barrel and slide remain locked together until after the bullet is gone, and the full force of their rearward momentum isn't passed to the frame until later. That is not the case with a revolvers.

JohnKSa is going to do a similar test as well. He will also lock the slide for part of the shot comparisons. Locking that slide would also show us a different result -- and give us some idea of whether a locked slide and barrel assembly increases recoil-induced barrel rise. A semi-auto fired with the slide locked ought be functionally similar to a revolver in terms of recoil effect.

 

[David R]

Apologies. Stuck working till after dark. No test tonight.

 

[David R]

200 grain SWC chronographed 845 fps out of my 3.5" colt lightweight officers model

230 grain ball. I do not know the velocity, these are old factory loads.

10 paces, 6 o'clock hold, almost dark.

I will do it again with a 5" 1911 target I have. I bet the difference will be less.

David

 

[David R]

Easy to tell which one this 45 likes. It's always been a tack driver.

 

[JohnKSa]

I think I've come up with a better way to lock the slide than putting my thumb behind the slide. I believe a heavy-duty plastic zip-tie looped around the front of the triggerguard and around the back of the slide will work.

I'll have to use a new zip-tie for every shot but that shouldn't be a problem since I don't need to shoot hundreds of rounds for the experiment.

 

[David R]

I am I this for other reasons than proving a heavier bullet hits higher in a hand gun. I have no problem with the physics, I took a course. I do not need the formulas or calculations, that is over my head.

The part about the slide and barrel moving before the bullet exits surprised me. It makes me wonder about accuracy. I have worked on 1911 a little. Once the slide moves the smallest amount, lockup is not the same.

David

 

[Walt Sherrill]

The part about the slide and barrel moving before the bullet exits surprised me. It makes me wonder about accuracy. I have worked on 1911 a little. Once the slide moves the smallest amount, lockup is not the same.

Not really.

As I understand it, until pressure drops dramatically -- which it can't do in until the bullet has left the barrel -- the force of the burning powder-created gases (which propels the bullet and causes recoil) will keep the barrel and slide locked tightly together until pressure drops. Then, in the 1911, the barrel link will start pulling the barrel out of the slide as they both more to the rear, causing the chamber end of the barrel to drop. Accuracy can't be greatly affected much in that first .10" of slide/barrel travel. The barrel and slide don't unlock until the barrel and slide have moved farther to the rear, and the bullet is long gone by then.

The part of the process that several of us can't get clear in our minds, is how the bullet's travel affects barrel rise in a semi-auto, prior to bullet exit. The motion described seems to delay (slow/postpone/slow?) much of the recoil force's transfer to the frame, however briefly. (Recoil isn't really stopped or delayed -- only the way it's transferred to the frame is in question.)

With a revolver, the barrel and frame are a single unit, and the rearward force of recoil causes the bore to rise.

With a semi-auto, there is a small force applied to the frame before the bullet leaves the barrel -- via the slightly compressed recoil spring assembly -- but most of the rearward force doesn't seem to hit the frame until the slide and barrel have continued their rearward movement Then recoil hits the frame from both the barrel and slides's direct contact with the frame and the slide's indirect contact via the recoil spring assembly.

 

[David R]

I THOUGHT the barrel and slide were solidly locked until the bullet left the barrel. Once pressure dropped things started moving so recoil would be the same as if it were solid. If the barrel and slide are locked, the slide should not move. Never saw a slow vidio.

 

[Walt Sherrill]

If the barrel and slide are locked, the slide should not move. Never saw a slow vidio.

Why should the slide not move? What's stopping it?

The slide and frame are NEVER really solidly locked together, unless you've got the hammer cocked and the thumb safety flipped up. Otherwise you can easily move that slide by just pushing it to the rear. Click the thumb safety off, and the slide is free to MOVE!!! That's not physics -- that's how most semi-autos work.

The barrel and slide are locked together, NOT the slide and frame -- and the barrel and slide remain solidly locked together until pressure drops -- which only happens AFTER the bullet leaves the barrel. (The bullet leaving the barrel opens up the front end of that high-pressure chamber.)

Here's a video I posted earlier. You can see slight slide/barrel movement to the rear.

http://i768.photobucket.com/albums/xx324/Mosin9/1224776345306.gif

And another I just found:

http://i768.photobucket.com/albums/xx324/Mosin9/1224776513887.gif

You'll notice that there is no visible upward movement of the barrel from recoil. (That doesn't mean it isn't there -- as only a small fraction of an inch rise at the muzzle can have a big effect farther down range. We're still trying to address THAT point in this discussion.)

 

[Metalboy]

There are lots of photos/videos on the net about what happens in the moment the bullet leaves the barrel. Here is some for you.

http://www.telegraph.co.uk/news/sci...of-the-microsecond-a-bullet-leaves-a-gun.html

 

[David R]

Thank you!

 

[JohnKSa]

I THOUGHT the barrel and slide were solidly locked until the bullet left the barrel. Once pressure dropped things started moving so recoil would be the same as if it were solid. If the barrel and slide are locked, the slide should not move.

The slide and barrel are locked together so that they move as a unit, not locked so that they can't move at all. They definitely move, but until they unlock (which happens after the bullet is out of the bore) they can only move together.

Here's a good video showing the slide and barrel moving together before the bullet exits.

I started the link partway into the video at the point of interest and you should be aware that if you start at the beginning there is a movie soundbite that some may find offensive in the soundtrack.

https://youtu.be/G0VjdI_S_HM?t=1m6s

Here's one of a revolver fired in slow motion. Stop the video just as the hammer drops and put a post-it note on the screen so that it lines up with the line of the barrel. Now let the video run and stop it just as the bullet exits. Notice how much the barrel has lifted in that timeframe.

https://youtu.be/VSlnLBcWbHA?t=33s

Here's one of a 1911 fired in slow motion. Again, stop the video just as the gun is fired and put a post-it note on the screen so that it lines up with the barrel. Let the video run and stop it again just when the bullet exits. Note that there is no detectable muzzle rise.

https://youtu.be/QA2gaCL3Z28?t=40s

Here's another slow motion video of a semi-auto pistol just to see if the 1911 video was a fluke. Using the same technique it can be verified that there's no detectable muzzle rise.

https://youtu.be/7y9apnbI6GA?t=10s

 

[JeffK]

Interesting! I do see barrel rise with the 1911 Colt, perhaps not as much as with the Webley (which has a longer barrel, too, and possibly a slower bullet, so it may be apples vs. oranges).

The main thing I notice, though, is that with the Webley there's an enormous volume of smoke that blows out the barrel and the cylinder gap, long before the bullet leaves. This will certainly also have some impact on how the gun moves before the bullet leaves the barrel, particularly a slow bullet in a long barrel. I'm surprised how much blows out early on, and whether a modern revolver would show the same thing.

 

[Walt Sherrill]

Interesting! I do see barrel rise with the 1911 Colt, perhaps not as much as with the Webley (which has a longer barrel, too, and possibly a slower bullet, so it may be apples vs. oranges).

I didn't see any barrel rise with the semi-autos, and I did as JohnKSA suggested, used a post-it note aligned with the barrels on the screen. (I'm not saying it's NOT there, but it's not easily seen.)

On the other hand, I was surprised that the Webley rose as little as it did. (align the post-it note with the underside of the Webley barrel and it's visible, but not as great as you might expect.)

The main thing I notice, though, is that with the Webley there's an enormous volume of smoke that blows out the barrel and the cylinder gap, long before the bullet leaves. This will certainly also have some impact on how the gun moves before the bullet leaves the barrel, particularly a slow bullet in a long barrel. I'm surprised how much blows out early on, and whether a modern revolver would show the same thing.

I don't know how smoke gets in front of a bullet, as the smoke is all created BEHIND the bullet, by the burning of the propellant that's driving the bullet forward. Unless the bullet is not well fit to the barrel, I don't know how it gets there in front of the bullet. Even when it smoke escapes from the cylinder gap, the bullet is ahead of it, and THAT "smoke" is a different (lighter) color. Start that video at about 37 seconds and click it on and off...

What you may be seeing is something other than smoke -- like moist air being compressed by the bullet's rapid movement. Maybe compressed air looks different in this type of situation?

The gas escaping from the barrel/cylinder gap certainly will affect (lower) the
velocity of the bullet as it later leaves the barrel.

Here's the video I posted earlier and there's no obvious barrel rise there, but the amount of rearward motion is clear, thanks to the calibrated marks on the paper attached to the slide and frame. http://s768.photobucket.com/user/Mosin9/media/1224776513887.gif.html

 

[JeffK]

You can see clearly when *something* (I assume the bullet) blows out of the barrel long after the smoke does. Smoke starts just after 0:37, and what looks like a bullet flies out at about 0:38 and a half. I don't understand it either, but unless something that looks like a bullet flies out the barrel long after the bullet does, then the smoke is in advance of the bullet. If the bullet exit is really much earlier than 0:38 and a half, then the barrel rise is going to be much smaller than the small amount you see at that time (and someone is going to have to explain what flies out at 0:38 and a half...).

 

[Walt Sherrill]

It is puzzling, but what you're seeing may not be SMOKE.

What we may be seeing is DENSE moist air which isn't as transparent as the air around the weapon. The lights used for the video are making it look dark just like moisture in a cloud makes a rain cloud appear dark when hit by sunlight. Or it may be residue from prior shots still in the barrel being pushed out by the next shot... Each shot will leave some.

I'm guessing... that's for sure.

Anybody got a better explanation?