Recoil and Barrel Length

[1911Tuner]

Two short stories.

Back in the summer of two thousand-ought-seven, I offered room and board to Wild Bill Caldwell...noted knife maker, pistolsmith, and mad scientist from down Louisana way while he was here to take an engraving course at Montgomery Community College.. We'd had a few discussions on velocities and recoil, and he'd just come into a batch of RG .38 caliber snub nosed revolvers that were tossed into a deal he'd made on some other guns and parts. Figuring that the parts might be useful for somebody, he kept them.

The barrels on RG revolvers are easy to remove, being no more than a pot metal shroud with a liner, and only pinned in place...and extremely lightweight. We chose the best three for out test. Two had nearly equal barrel/cylinder gaps, and the third was to be barrel-less...so the gap didn't matter. All chamber throats were consistent enough to make no practical difference.

One would retail its barrel as the control. The second, I removed the barrel and shroud, and used the lathe to cut the barrel back to bare minimum, leaving just enough of the forcing cone to provide very shallow rifling so that the bullet would be stable enough not to tumble and destroy the chronograph. The length came in at just over a half-inch. The third gun had no barrel, and was to be fired through the hole in the frame. Ammunition was standard velocity 158 grain lead round nose.

The first two guns were chronographed with 5 rounds and averaged. I don't recall the exact numbers, but I do remember that the difference between 2.1 inches of barrel and a half-inch of barrel was just 42 fps. We couldn't detect any difference in recoil for any of the three guns, and a friend who arrived during the experiment couldn't, either...even in a blind back-to-back test in which he closed his eyes and fired the guns that we handed him in succession. On one, he actually picked the half-inch barrelled gun as "Uh...maybe...I dunno. Hard to tell." kicking the hardest.

Curiosity got the best of us...and figuring "What the hell." It was an old Chrony, and I wanted an excuse to buy a new one...so we decided to see if we could clock a few through the one with no barrel. Not only did we not shoot the machine, but we got some good numbers. The difference was just 58 fps between the barrelled control gun and the one with no barrel. Although I can't prove it, it's very likely that the bullets were...if not tumbling...at least yawing as they crossed the screens, which would tend to lower the velocity a bit.

Story #2 was an accident, and actually a slightly embarassing tale that I have to tell on myself. It entailed a session at the falling plate racks just for a little recreation with a pair of my single-action revolvers.

One...a 4.625 inch .41 Magnum Blackhawk, and the other a .45 Caliber New Vaquero with the same barrel length. Luckily, my .41 Magnum range ammo is loaded well below maximum...consisting of a 210 grain cast bullet and 8 grains of Unique. The standard .45 Colt load is a 250-grain cast bullet with the same powder charge.

In the middle of the shoot, a guy in the next bay approached me to talk about a little problem he was having with a 1911, and...thus distracted...I slipped 6 rounds of .41 ammo into the Vaquero. I didn't catch it until I ejected the badly bulged, but not burst empties. The odd thing was that I knocked 5 out of 6 plates down at 20 yards...and they were knocked down with just as much force as they were when hit by the correct gun/ammunition combination. Any recoil and report difference likewise went undected...and I shoot those revolvers a lot...so if there had been any real difference, I'd have noticed it immediately. I know that cast bullets will obturate and seal the bore in a gun...but I don't believe that they'll bump up .040 inch.

I understand that as long as the bullet is in the barrel and being accelerated, it generates an equal force push on the gun. BUT...What little is gained in the barrel after the initial punch is of little consequence compared to the peak impulse. While I'm certain that the difference is measureable...it's undectable by the human hand. It's over before the information reaches our brain.

And...Discuss!

 

[CraigC]

Conventional wisdom has always held that longer barrels transmit less felt recoil to the shooter. Felt recoil is highly subjective but in actual shooting, the opposite has always been true for me. Shorter barrels have always been more pleasant to shoot. This is quite apparent in shooting my two custom Ruger Bisley .44's. One a 4 5/8", the other a 7½", both with identically profiled custom grips. Could be that the shorter barrels expend more energy in muzzle flip and that longer barrels transmit more straight back into the palm. Noted gunsmith and handgun hunter Gary Reeder, who I quite notoriously don't get along with, postulates that shorter barrels have less leverage against your wrist. I don't care for him personally but have to agree with him on this.

 

[Manco]

I just want to explain that in the other thread where this topic came up, I was using the very specific scientific definition of impulse, which is a change in momentum that is related to force over time, in trying to refute something that you said while using a different definition of the English word impulse (i.e. peak force or acceleration). I thought impulse was supposed to mean the same thing to everybody with regard to recoil (it was always about momentum in my previous discussions, and that is the scientific meaning), but apparently that's not always the case. Obviously if we were using different definitions of the same word, then we were really not saying much that was coherent. Nothing that I've said was incorrect, and nothing that you've said was incorrect, to my knowledge, as we were talking about two different things.

 

[1911Tuner]

we were talking about two different things.

I was responding to a post...can't remember who wrote it...in which it was stated that a shorter barrel would produce less felt recoil due to the lower velocity. My stance was that muzzle velocity has very little bearing on felt recoil, and that...assuming two guns that are equal in all except barrel length...that nobody alive could detect the difference in a blind test....although the equations can correctly prove that there is a difference.

I've talked to a good many people who believe that without a barrel, a fired round would result in a "phhht" and the bullet would drop to the ground no more than a foot or two in front of the gun.

I arranged a demonstration once with a badly worn and pitted 1911 barrel. After drilling it out from the muzzle to the chamber stop shoulder to a diameter of .495 inch. Before firing, the object of the demo was ready to wager good money that the bullet would drop on the ground, and the slide wouldn't budge. He was fairly shocked to see the slide move briskly...the empty eject and fly several feet away...and the bullet disappear into the hard, packed red clay that's so prevalent in the Southeastern US, kicking up a sizeable divot as it did. Unconvinced, he wanted me to shoot it again. The second round did likewise in a hardwood tree. Still skeptical, he had to shoot the gun himself before he became a believer.

Typical pistol rounds...charged with the powders used...reach about 90% of their velocity and produce about 95% of their total recoil impulse within a half-inch of bullet travel. Even the magnum revolver cartridges with their slow-burning powders will do it within an inch or so. As the bullet moves through the barrel, peak pressure and force drop rapidly because of the increasing volume of the cylinder. Because the bullet is moving and gathering momentum, the force requirement to accelerate the bullet is lower the faster the bullet goes...and because force forward is force backward...so the recoil impulse drops as the bullet continues to accelerate through the barrel.

The longer barrel does generate more measureable recoil...but we'll never detect it, except possibly in a very long barrel with a very slow powder pushing a heavy bullet.

And...as I stated earlier...With a quick number like Bullseye or HP-38...it's very likely that the bullet is actually moving faster at mid-point in the barrel than it is at the muzzle...so as the bullet starts to decelerate in the barrel due to friction and falling pressure...it starts to exert a forward drag on the gun, which would tend to counteract the recoil a bit. Go to a slower powder, and you start over with a whole new set of dynamics. The question is too long, wide, and deep to make a flat statement that the higher the muzzle velocity, the harder the gun kicks.

 

[MrBorland]

I was responding to a post...can't remember who wrote it...in which it was stated that a shorter barrel would produce less felt recoil due to the lower velocity.

Hi, Tuner - In case it was mine (see below, post #49), I should clarify that I didn't relate barrel length to felt recoil, but rather to "intrinsic recoil", which is my coined term for the objective and measurable distance the gun moves while the bullet is still in the barrel. In other words, all else being equal (e.g. total weight), and felt recoil aside, barrel length increases "intrinsic recoil". I also suggested (post #53) several controlled experiments which could be used to test the theory.

I don't doubt the validity of the experiences you relate here, and common sense tells me they are correct, but they relate more to felt recoil and less to intrinsic.

http://www.thehighroad.org/showthread.php?t=540863&page=2


Edit: I re-read your post and understand your point a bit better now - that you showed that the bullet, for all intents and purposes, has stopped accelerating very early in it's travel, so the back-pushing force therefore stops long before the bullet reaches the end of even the shortest barrel. Logical enough, since your experiments show that a bullet reaches near peak speed even without a barrel. But "near peak speed" is an important qualification, and looked at another way, your data show the bullet doesn't reach peak velocity that early, since the difference between your 2.1" and 1/2" gun was 42fps. This clearly shows that the bullet is still accelerating after 1/2".

As the bullet moves through the barrel, peak pressure and force drop rapidly because of the increasing volume of the cylinder.

I'll make the same point I made earlier: even if peak pressure drops as the volume of the cylinder increases, it doesn't drop to zero - how can it? There's still hot gas behind the bullet, so the pressure must be above ambient. If there's still pressure, there's still force, even if it's way less than peak.

Because the bullet is moving and gathering momentum,

A bullet doesn't "gather momentum" unless it's increasing it's velocity, which, by definition, is acceleration, and, by definition, requires a force to do so.

The longer barrel does generate more measureable recoil...but we'll never detect it, except possibly in a very long barrel with a very slow powder pushing a heavy bullet.

I suspect you'd easily detect it by allowing 2 identical guns, save barrel length, to recoil freely in a ransom rest. This was part of the test I proposed, and maybe someone will give it a try. Be prepared for some "peer review", though.

 

[1911Tuner]

even if peak pressure drops as the volume of the cylinder increases, it doesn't drop to zero - how can it? A bullet doesn't "gather momentum" unless it's increasing it's velocity, which, by definition, is acceleration, and, by definition, requires a force to do so.

Of course it doesn't, unless the barrel is so long as to burn the powder completely up before the bullet reaches the muzzle. It simply takes less pressure and force to keep accelerating the bullet than it took to get it up to whatever the speed was at peak pressure.

Let's try again with three hypothetical guns.

All of them are identical weight/mass and caliber. One has a 2-inch barrel and the other an 8-inch barrel. We'll leave the 3rd one for another phase.

Let's assume identical bullet mass/weight. Let's assume that the longer gun produces a velocity of 1,000 fps from its 8-inch barrel. Let's juggle the powders so that we can produce the same velocity with the same bullet from the 2-inch gun.

Common sense tells us that the shorter gun will require a faster powder and a much higher pressure to generate the same velocity because the rate of bullet acceleration must be four times that of the longer barrel. The shorter gun will recoil much more intensely...even though the muzzle velocities are the same.

For the 3rd gun... Let's put a long barrel on it...so long...and the powder charge so perfectly matched to that barrel length...that it completely peters out just as the base of the bullet reaches the muzzle...and the bullet merely pops out and falls to the ground.

This gun will also recoil...even though the muzzle velocity is zero.

Back to the original point.

Although muzzle velocity is an assumed result of firing a bullet through a barrel, it has nothing to do with the level of recoil produced. It's related only in that the bullet is accelerated for a given time at a given rate, but recoil is the result of acceleration.

What we see and most of what we feel as recoil is actually momentum that was generated by that acceleration. The gun moves very little while the bullet is in transit...but it continues to move after the bullet exits...and after all accelerating force is removed from the gun and the bullet.

Also, there's no argument that a claimed or proven muzzle velocity can provide a pretty good estimation of what we can expect in the way of recoil, that's all it is...guesswork.

 

[Manco]

The longer barrel does generate more measureable recoil...

And that's ALL I meant by "impulse" (the official scientific definition)! I had mistakenly assumed that everybody used the very same definition. In my view, that's the only valid use of the word in the context of describing physical phenomena, and any physicist would agree (I know we're not all physicists, but it doesn't hurt to stick with established convention in such cases). In fact, until now every discussion I've ever had involving recoil not only defined "impulse" as the change in or transfer of momentum, but also defined "recoil" itself as the impulse. The latter is not necessarily an "official" definition, but the former is.

Had I realized that you used the word "impulse" to refer instead to the peak instantaneous force or acceleration, I would not have said a word, but it's not easy for me to simply throw all that out the window, so to speak, and use new definitions of words, hence the misunderstanding.

but we'll never detect it, except possibly in a very long barrel with a very slow powder pushing a heavy bullet.

That was the very point I was originally trying to make--that despite the fact that the "impulse" is actually greater in 4" barrels than 2" barrels (whether by a large or small amount is irrelevant--it's greater at least in this simplified version of reality), the perception of recoil does not necessary follow, and could well be the opposite (then I gave some plausible reasons for that). Then you said this was not true, but you were using your definition of "impulse" rather than mine--there's the second misunderstanding. :banghead:

That's OK, I did it first, and there was no harm done, except for me feeling silly--now I understand how realistic sitcoms can be. Then again, maybe I shouldn't feel silly--ask any physicist and they'll give you the exact same definition of "impulse" that I used here and have always used everywhere.

 

[Manco]

Common sense tells us that the shorter gun will require a faster powder and a much higher pressure to generate the same velocity because the rate of bullet acceleration must be four times that of the longer barrel. The shorter gun will recoil much more intensely...even though the muzzle velocities are the same.

Right, at least in fixed-barrel guns there is no doubt that felt or perceived recoil is heavily influenced by the dynamics of the instantaneous acceleration curve. I believe that this is what many people would refer to as "snappiness."

For the 3rd gun... Let's put a long barrel on it...so long...and the powder charge so perfectly matched to that barrel length...that it completely peters out just as the base of the bullet reaches the muzzle...and the bullet merely pops out and falls to the ground.

In reality I think that the bullet would have a lot more momentum than that! What I'm saying is that the powder would have stopped burning and the pressure would have dropped to ambient well before the bullet reached the muzzle and just popped out. With that in mind, let's continue the thought experiment.

This gun will also recoil...even though the muzzle velocity is zero.

The bullet was initially given some momentum, and then it gave that momentum back through friction in the barrel, hence the impulse (scientific definition: net transfer of momentum) from the start to end time of the bullet's travel is 0, which is what we'd expect from multiplying its mass by its muzzle velocity, which is 0. The gun will initially kick back hard (high peak force resulting from high peak acceleration, F = ma) and then pull forward more gradually (lower force over a longer period of time). If you define "recoil" as impulse, which makes sense for 2" and 4" revolvers, then technically the gun has no recoil. On the other hand, by other definitions, you could say that it recoiled, as the shooter certainly would feel something!

Back to the original point.

Although muzzle velocity is an assumed result of firing a bullet through a barrel, it has nothing to do with the level of recoil produced. It's related only in that the bullet is accelerated for a given time at a given rate, but recoil is the result of acceleration.

If that's how you define recoil, which in that case would be more completely described as force--the mass of the bullet multiplied by its acceleration. Impulse, however, is not force but the integral of force over time, representing the total change in momentum over that interval. This is how many other people define recoil, and for good reason. By the laws of physics, the impulse can also be calculated by multiplying the mass of the bullet by the change in velocity over the interval, which is why velocity is relevant to how many people estimate "recoil." Your definition of recoil is just different, and that's OK as long as that's clear, but the fact that your definition of "impulse" is also different just makes things even more confusing.

What we see and most of what we feel as recoil is actually momentum that was generated by that acceleration.

I thought you were saying or implying that most of what we feel is actually force rather than momentum. In reality both can affect perception. The change in momentum or "impulse" is what I've been using to define and estimate recoil, and I have the equations to back it up. What you seemingly just said supports this view and what I've been saying all along.

The gun moves very little while the bullet is in transit...but it continues to move after the bullet exits...and after all accelerating force is removed from the gun and the bullet.

That's what momentum does, so I guess you really are talking about momentum...now...but not earlier.... No offense, but your use of terminology is killing me. To me, impulse and recoil are the same, and have a single, very specific definition. Everything else gets its own term, such as "snappiness" or "instantaneous force."

Also, there's no argument that a claimed or proven muzzle velocity can provide a pretty good estimation of what we can expect in the way of recoil, that's all it is...guesswork.

It's a simplified version of what really goes on, but since the bullet is typically still accelerating when it leaves the barrel of a typical gun, I don't think that friction and other factors have a major effect on the estimation. I think you just gave a ringing endorsement of how most people view recoil, but your other view is just as valid and may sometimes play a bigger part in perception, depending on the individual, the gun, the caliber and load, and other factors.

Now what I'd really like to know is why and how all of these complexities at least appear to also apply to short-recoil-operated autoloaders despite the barrel being mostly "disconnected" from the shooter while the bullet is still accelerating.

 

[MrBorland]

Tuner - you make a good point, and I realize another clarification is in order: That intrinsic recoil* is linearly proportional to barrel length is easy to show mathematically, and gets the general point across, but it's an overly simplistic model. In reality, as you show, peak pressure falls off rapidly and continues to fall, and therefore so does force. Yet the pressure is still there, and therefore so is force, albeit lower. So while intrinsic recoil* and barrel length are proportional, it's not a straight linear relationship. The relative measurable difference between a snubbie and a service revolver is therefore likely to be greater than that between a 16" and an 18" carbine.

Common sense tells us that the shorter gun will require a faster powder and a much higher pressure to generate the same velocity because the rate of bullet acceleration must be four times that of the longer barrel. The shorter gun will recoil much more intensely...even though the muzzle velocities are the same.

Yes, the recoil impulse and perceived recoil will be greater from the shorter gun. Once again, no argument here, but perceived recoil or recoil impulse in this context is a straw man argument, since I've been considering the distance the gun will move while the bullet's in transit, not recoil impulse or perceived recoil.

I predict that, if fired from a ransom rest and allowed to freely recoil, the round from the 8" barrel will consistently hit higher than the round from the 2" gun, and do so no matter what ammo is used (so long as both guns are otherwise identical and the same ammo is used in both guns).




* For the record, I define "intrinsic recoil" as the relatively small distance the gun moves while the bullet's still traveling down the barrel. It does not refer to total muzzle rise, recoil impulse, energy, or perceived recoil.

 

[chriske]

Most of this is way over my head, but FWIW : I once (not on purpose) shot a couple of .44 Spl reloads out of my .45 Colt Ruger Blackhawk.
The difference in report and recoil were VERY noticeable and accuracy was nonexistant.
No-one /nothing was harmed BTW.

 

[Manco]

since the bullet is typically still accelerating when it leaves the barrel of a typical gun

Just a clarification. I meant that the bullet is still being pushed by a force and is therefore still accelerating at the very instant that it leaves the muzzle. What I did NOT mean to imply, in case anybody took it this way, was that the bullet is still accelerating after it clears the muzzle. Over the years I've come across more than a few people who had such a notion, and it is definitely false. Drag is pushing the bullet back and gravity is forcing it downward, but nothing is pushing it forward once it's completely outside of the gun.