How is velocity affected by Locked Breech, vs Delayed Blowback, vs Blowback?

[brickeyee]

Just to throw a little detail on rates of acceleration.
The derivative of acceleration is called ‘jerk’.
It can be viewed as how ‘sharp’ the acceleration is, but is usually only encountered in tool and machinery design were smooth (low/no vibration) operation is needed.

You can play around with Quickload and see how the acceleration rate of the projectile changes, but the entire thing is so short you really are unlikely to feel much unless you make a large change in powder burning rate while preserving the same muzzle velocity.

Recoil occurs so quickly that the body cannot even change muscle tension during the barrel dwell time. Nerve conduction is just to slow. What you had as the hammer dropped is what you have as the bullet exits.

 

[1911Tuner]

Proof

I am keeping it in mind. I know that "felt" recoil is subjective, and depends on too many variables between individuals to call...but as it stands, we're trying to figure out exactly what the mechanics are in the effects of longer barrels to shorter ones. Whether the increase in velocity has any measureable effect on the recoil impetus.

Actually...we've taken it off-topic, since the original question was dealing with
velocity loss between locked breech and blowback. Ah well...

And...Yes. I do use that method. Three rounds...Handloaded 250-grain jacketed bullets with enough Unique to trip the chronograph at 950+ fps.
Not true proof-level...but enough to do what I want it to do...and I haven't cracked a lug yet, not even with modern barrels. It takes about 2,000 rounds of standard stuff with a tightly-fit barrel to get the same effect. A little less if I shoot the barrel hot.

The point is that, if frictional resistance to bullet acceleration weren't pretty high, the lugs wouldn't seat that quickly from firing three heavy handloads OR 2,000 rounds of hardball.

 

[jungle]

Barrel time in most any firearm is less than 1 millisecond, this is as one poster pointed out, outside the range of human perception. Although many claim more or less felt recoil with faster or slower powders at the same muzzle velocity, it is really quite beyond human ability to actually feel the difference.
Maybe I'm just insensitive.

In the case of the 1911 and barrel lugs friction still plays a small part. The slide is under pressure from gas at one end and the barrel is being forced forward by a column of gas restrained by the limited ability to accelerate a mass at the other. If there was no friction at all, the ability of the gas to accelerate the bullet is still limited by inertia and total available energy.

If you were to remove most of that friction, as you did in your barrel experiment, the bullet still flies and the pistol operates normally. Chop the barrel off just ahead of the chamber and velocity and friction both drop off. Velocity because the gases are not allowed to act as long and friction, because there is no barrel.

See how very little Bullseye will drive a bullet out of a barrel.

 

[1911Tuner]

re:

Jungle wrote:

>Barrel time in most any firearm is less than 1 millisecond, this is as one poster pointed out, outside the range of human perception.<
***********

Exactly. (We agreed! Hell just froze over.)

Now...on to the effect of longer barrel/increased velocity.

As the bullet's frictional and inertial resistance to acceleration falls off with that acceleration...so does the force required to accelerate it. As the force required to move the bullet forward falls off...so does the force applied rearward against the breechblock. Force in one direction equals force in the other.

So the questions remain:

Can a human being feel a difference in recoil with different velocities in the same weight gun?

Remember that we're not talkin' about a huge difference in velocity. (Plus the fact that factory ammunition often varies that much or more from shot to shot.) I have serious doubts. At roughly 35 fps per inch of barrel, it would require a 2-inch barrel versus a 20-inch barrel before it even started to show....assuming equal gun mass. If you can't tell the difference in velocity variation between rounds in the same gun, you sure ain't gonna be able to feel it between a 4-inch barrel and a 6-inch barrel. There just isn't time to feel it.

And:

Does the frictional and inertial resistance of the bullet that's pulling forward on the gun get cancelled out by the rearward force against the breechblock, rendering each one a neutral player in the entire sequence? (Which would leave the initial impulse...the "punch"...as the sole source of felt recoil.

 

[jungle]

Can a human perceive small differences due to recoil variations caused by small velocity differences? No, but the difference in a .38 and a .357 will be readily apparent in the same weight revolver.

Recoil is a far bigger player than friction or inertia and this is why recoil operated guns work and why we feel recoil. Recoil will always be the result of mass and velocity. The muzzle velocity and the mass of the bullet will be expressed as momentum and it will equal the momentum of the gun when weight is given and velocity is computed. Newton's Third cannot be denied.

 

[1911Tuner]

Newton

Not tryin' to deny Newton's 3rd Law...Simple sayin' that 95% of the recoil and probably about that much velocity is generated in the first half-inch or less of bullet movement.

Think about it carefully...

Handload a .45 caliber round with a 200-grain bullet to purposely produce less than 600 fps muzzle velocity...and a normally-sprung 1911 slide will short-cycle. Why else do the "Softballers" have to drop to 12-pound or lighter springs to get their target loads to cycle their guns?

Load one to produce 830 fps...and then remove the rifling like I did to prevent full pressure peak...which probably produced about the same muzzle velocity as the softball load, or at least close...and the gun cycles just fine. Remember that there was no restriction to the bullet's acceleration other than the size of the chamber at the shoulder, and nothing to drive pressures up AFTER the initial impulse. Essentially, the bullet was being fired through a zero-inch barrel, so velocity couldn't increase after the impulse. If anything, it would probably slow down. Yet, the gun recoiled and the slide cycled full rearward.

 

[jungle]

I don't think an 830 FPS load will go 600 FPS out of a zero inch barrel. Your barrel experiment showed the column of gas was still able to accelerate the bullet despite much more than normal gas leakage.

What you are really proposing is that 95% of velocity(and recoil) is generated in the first half inch of bullet travel. And we both know this just isn't happening. Are you saying the rest of the barrel only contributes 5% of velocity?

Think back to your example of no bullet movement equals no recoil. Exactly so, and the faster the bulllet moves the higher the recoil.

 

[1911Tuner]

re:

>>What you are really proposing is that 95% of velocity(and recoil) is generated in the first half inch of bullet travel. And we both know this just isn't happening.<<
**************

That's exactly what I'm proposing...and I think that's exactly what's happening...and I'll come up with a way to prove it. Not with mathematical equations. With a gun. Hopefully, when you make the trip to the NC coast to visit your family, you can set aside a day to come see/come say, and stay for supper. It's not more than 4 hours away.

 

[jungle]

It would be easy enough with a scrap barrel stub clamped into a slide stub and chronoed with a barrel length allowing a half inch of bullet travel. 95% of 830 is 788 FPS. I'd guess closer to 350 FPS, but as they say the proof will be in the actual measurement. Put me down for 350 FPS or less and let the next experiment begin.

 

[1911Tuner]

It Begins

Well...I don't have a stub slide... but I may be able to arrange somethin' close. The problem is gettin' the bullet to fly straight enough to keep from bustin' the chronograph. Besides...the slide would be about 1/3 the mass of a non-stubbed slide, and that wouldn't show that it'd make full slide travel.

You can prove it yourself if you're willin' to spend a little money and be in violation of a serious law for the few minutes required.

Go find a beat-up single-shot shotgun in a pawnshop. Fire it at a 55-gallon drum from about 30 paces. Take note of the lapse in time from bang to shot charge impact. Use buckshot.

Lop the barrel off to dead flush with the end of the shell...and fire it again.
Bet it'll kick just as hard...harder actually...and if you can detect a difference in the flight time of the shot charge, I'll pay ya for the gun. If you can't, you pay me the cost of the gun.

Destroy the "barrel" immediately afterward. It'll getcha a five-year, all-expense paid vacation at Club Fed if you're caught with it on the same property with the receiver.

 

[jungle]

My ability to detect a difference in flight time would be zero. This is not true of a chronograph however. Shotguns will be even bigger losers of velocity than pistols as barrel length diminishes. Why? They have more powder to burn and it takes a longer barrel to allow complete burning under pressure.
A 1911 with a 5 inch barrel is about like a .30-06 with a 42 inch barrel in terms of bore to charge volume.

 

[1911Tuner]

re:

Okay, jungle...But go try it. Bet it'll kick as hard or harder with no barrel. You can detect that. If there's very little projectile acceleration without a barrel to contain and direct the gas column, the gun should barely kick, and the shot charge shouldn't travel more than about 10 or 20 feet...right? At the very most, the recoil should be only a small percentage of the potential because the projectile velocity should only be a small percentage of the potential. Meaning the potential that it would produce with a 20-inch barrel.

Go ahead. Try it. Bet it'll rattle your teeth...

 

[jungle]

Well you got me, all these years I thought barrels were a method of increasing bullet speed. Now I find out they are just a place to put sights and a handy handle. That settles it, I'm cutting them all back to a half inch. Now where is my hacksaw?
I reckon they'll be a might handier, somewhat lighter and 95% as efficient so why not.
Next thing I'm going to do is remove the center of gravity so they'll be lighter.

 

[1911Tuner]

re:

Now Jungle...Don't go gettin' all condescendin' on me.

One way to find out is to unscrew the barrel from a revolver and shoot it.
If losing length of barrel costs 35 fps per inch...that would be a drop of
140 fps from a .357 magnum. A 158-grain bullet starting at 1100 fps is still pretty healthy...and I doubt if you could tell the difference on either end.
Easy to do. Any gunsmith should be able to remove and replace the barrel
for ya with no ill effects afterward. Shoot it into a test medium to test penetration, and allow for the tumble that the bullet will probably take, which will limit penetration somewhat. Bet the results will be a surprise.

The old West gamblers used to do that with .45 Colt SAAs, and they were pretty nasty and deadly across a poker table...with the bullet often shooting
clear through their target sideways. Google it. Read about it. Come see us.
We'll run some experiments that'll open your eyes.

Cheers! Out!

 

[JohnKSa]

I think 95% is high, but there's no denying that a very large portion of the velocity comes almost immediately.

If you run the 20fps per inch thing backwards towards the breech from a typical muzzle velocity, you'll have lots of fps left over when you run out of inches.

 

[jungle]

Just one little detail. 20-30 FPS is a simple rule of thumb that applies to normal barrel lengths. The curve is not linear. Make the barrel long enough and it starts to flatten(less gain), make it short enough and it starts to steepen(more loss). This is one of those questions that defies a simple rule and would require testing as proof.
We don't normally encounter half inch barrels on firearms. Wonder why?

 

[1911Tuner]

re:

John...Exactly. If we add roughly 35 fps per inch...where did all that velocity come from before the bullet hit the barrel. 95% may be a bit high...but I bet it won't be too far off the mark...and I'm pretty well satisfied that 95% of the recoil impetus comes in the first half-inch or so.

Jungle said:

We don't normally encounter half inch barrels on firearms. Wonder why?

Well...There are several reasons besides increasing velocity. Balance...Muzzle blast...Sight radius...Things like that have more practical signifigance than bumping muzzle velocity up an additional 50 or 60 fps.
A deer hit by a 240-grain, .44 caliber bullet at 1200 fps will go down swearin' it was 1250 that got him.
*******************

And:

>Just one little detail. 20-30 FPS is a simple rule of thumb that applies to normal barrel lengths. The curve is not linear.

I know. That's why I describe it as "roughly" X feet per second. Change powder burn rates, and it moves up or down the scale. Take the barrel length
beyond normal length...say 6 inches for a revolver...and the average again changes. Much of my gun work over the past four decades has been in load development, and I did come to some definite conclusions during that time.

Like the 4-inch shotgun barrel...Been there, done that. During my misspent and misguided youth, I've done several things with guns that would have landed me in deep trouble or in the morgue if my ol' man hadn't found me out before the local cops did...or before I blew my eyes out. See...me and this other fool decided one day how cool it would be to have a 12 gauge pistol...and we primed tobacco for a week for an old Topper single-shot. We just kept cuttin off barrel until a badly sprained wrist put a stop to it. Seems like I was about 14...but it's been a while. Daddy-O was NOT happy...just like the time that I cobbled up a silencer for a .22 rifle from an old lawn mower muffler. Then, there was the homemade blackpowder cannon that we used to shoot spark plugs through trees. Shot one clean through a tobacco barn...in one side and out the other. Lordy! The stories I could tell!

 

[ABBOBERG]

I have been following this thread closely because I am also trying to figure out how much velocity affects recoil. When I compare the felt recoil of the Kahr PM9 with a 2.95" barrel to the recoil of a same-size semi-auto I developed with a 4.2" barrel, the gun with the longer barrel seems to have a little less sharp recoil and slightly less "jump", but that could be because of the better grip (much taller backstrap) or the fact that the barrel rotates instead of tipping as it does on the Kahr. By the way, the velocity difference for these two guns is quite dramatic - I see an average of 110 feet/sec more with 18 different brands of ball ammo, and 140 feet/sec with 5 different brands of +P hollow points. The 30 feet/sec per inch rule does not apply when barrels are this short.

 

[1911Tuner]

30 FPS "Rule"

ABBOBERG...No argument. The 30 fps "rule" isn't a hard, fast rule, but rather a ballpark estimate. I have a pair of L-Frame Smiths...a 4-inch 681 and a 6-inch 686. The 4-inch gun regularly turns in equal or slightly higher velocities
with a given bullet than the 6-inch...depending on the powder burn rate used.
Even when the 6-inch gun comes out on top...such as when the ammo is loaded with very slow powders like Olin 296 or Hodgdon H-110...it's a very slight edge. Something on the order of 25 fps average for a 10-shot string.

The "rule" probably came as a result of a test in a gun mag that's been run a few times with both rifles and handguns, in which the writer started with a long barrel and cut it off in one-inch increments. A comparison between two
identical guns...save for the barrel length...isn't definitive, due to other variables that can affect the muzzle velocities.

 

[grendelbane]

I was all prepared to state my case about why long barrelled revolvers recoil differently than short barrelled revolvers, and then the phone rang, and I forgot all of my eloquent arguement.:banghead:

Tuner, your comments about the difference between the recoil of a 357 SIG, and a .357 magnum sounded interesting. I have noticed how much more comfortable the auto is compared to many revolvers I have fired, even though the ballistics of the 2 are very close.

It would be interesting to fire the .357 B&D (???), or the other 357 revolver wildcat whose name escapes me right now, (.41 necked down to .357).

Recoil is extremely subjective. I told an acquaintance that I had just about given up on revolvers, as I had gotten so sensitive to recoil, and was shooting mostly Gov't model pistols. He looked at me like I was an idiot, and said that made absolutely no sense whatsoever. Different people do indeed perceive recoil differently.

 

[JohnKSa]

20-30 FPS is a simple rule of thumb that applies to normal barrel lengths. The curve is not linear.

Right, in fact if you try to apply the rule at the extremes, you rapidly realize that there's something else going on. That was where I was going with that.

I do recall reading/hearing about a forensic savvy murderer (ex cop) using a revolver from which the barrel had been entirely removed to avoid leaving rifling marks on the bullet. Clearly there was enough velocity to "do the deed" even without a barrel to add velocity.

I suspect that there is a "popgun" effect when the bullet comes loose from the case that gives the bullet a large portion of its velocity almost instantaneously. Can't prove it, but I'll be interested to see the results of Tuner's test.

 

[grendelbane]

I suspect that there is a "popgun" effect when the bullet comes loose from the case that gives the bullet a large portion of its velocity almost instantaneously.

In Hatcher's notebook there is a graph of a .30/06 Springfield barrel which shows velocity and pressures at 1 inch increments.

I think that there is also a line representing acceleration.

Or, at least that is what my memory says. I can't seem to find my copy.

Anyway, while the 95% figure might be a trifle high, it stands to reason that acceleration is highest during the time that the pressure driving the bullet is highest.

I can not explain it any better than this. If my brain were a semi-auto pistol action, it would be best described as a retarded blow-back.

Which reminds me? Would any one like to see the Remington model 51 type action brought back in a modern style pistol? Or the Savage?

 

[jungle]

Try this. A more recent graph of time, distance, velocity and pressure. 5.56 Nato in standard barrel. It's amazing how long it takes that tiny, light bullet to start moving. Inertia is at work as things begin.

 

[JohnKSa]

jungle,

Do you know anything about the circumstances under which the graph was made?

It looks like perhaps the case was not crimped...

If that graph is applicable to handgun bullets, the ex-cop would seem to be have been very lucky to be able to deliver a lethal shot with his barrel-less revolver.

 

[jungle]

Military test, other than that don't know much about it. As far as I know all standard US military ammo is crimped and neck sealed with asphaltic material.

As far as the barrel-less revolver, the chamber should get the bullet out at 350-400 FPS and that would easily do the trick. I think the old Webley Irish Constable model was famous for it's effectiveness despite kicking it's large slug out at only 400+ FPS.