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

[1911Tuner]

re:

John...Are we gonna do it again? Stand ready, you scallywag!

The bullet causes the equal and opposite effect that we know as recoil for as long as it's in the barrel and moving. The longer it's in the barrel...and moving...the longer it works to impart that equal and opposite reaction. How much more after initial impulse results mainly in a longer time in recoil, but not a "harder" recoil. Hypothetically...Two pistols of equal weight...one with a 10-inch barrel and the other with a 5-inch barrel fired with equal rounds would result in the same "punch" in your hand. The longer tubed gun would just push for a little longer time. Could you actually feel a difference? Probably not. The difference in dwell time in the barrel would be tiny. It doesn't take long to accelerate a bullet another 200 fps once it's already moving...and it would get through another 5 inches of barrel like right now. Once the bullet is gone, recoil as we know it is over.

The..ejectiva... (John...ya gotta stop usin' these 20-dollar words on me.)...of the gasses also have an effect, but that effect in a pistol is, for all practical purposes...of no consequence. Roughly equal to the mass/weight of the powder charge at about the speed of sound. For a typical .45 ACP cartridge, that would equate to a 5-grain bullet at about a thousand fps. Recoil generated would be about 1/8th that of a .22 Stinger fired in a K-frame revolver.

The effect would be greater in, say, a .30-06 because of the heavier powder charge at higher pressures...and the fact that the bottlenecked case creates a sort of rocket engine...or a venturi effect...and causes the...ejectiva to accelerate as it escapes...Like the nozzle on a garden hose.

 

[JohnKSa]

Tuner,

Recoil is conservation of momentum--ignoring the other ejecta as a minor (or at least constant for our purposes) contributor, we have the following equation.

Bullet weight x bullet velocity = gun weight x gun recoil velocity

Let's say that muzzle velocity from a 5" bbl is 850fps.

Let's say that you get 20fps for every inch of additional barrel--that's 950fps muzzle velocity for the 10" bbl. If we assume that the average velocity of the bullet over the last 5" of barrel is about 900fps (split the difference between 850 and 900) then we can see how much longer the bullet is in the barrel.

The bullet is in the 10" barrel about 0.00046 seconds longer than in the 5" barrel. That's far below the time resolution measurement capability of your average human.

On the other hand, a 230gr bullet exiting a barrel at 950fps will impart 12% more momentum to the launching platform than a 230gr bullet exiting the barrel at 850fps.

Going back to the equation for momentum, we see that the left side of the equation is 12% bigger for the 10" bbl. As long as the additional 5" of barrel doesn't add 12% to the weight of the gun, the only thing we can increase on the right side of the equation to make ot balance is the gun's recoil velocity.

Increased recoil velocity means "harder" recoil. Trying to figure out how much harder it would feel is very subjective, but it's safe to say that there is some increase in momentum.

 

[1911Tuner]

Ejectiva

That still sounds like an STD...

John...I think your're forgetting one thing, and ignoring a second.

One:

Remember that bullet movement is the initiator, and bullet acceleration is an important player. i.e. The harder that you try to move something, the more it resists being moved, and the more force is required TO get it moving. Conversely...Once you GET it moving, the less force it requires to KEEP it moving.

I think that you're assuming that pressures are constant for the length of the barrel. Not so. Pressures peak quickly, and start to fall off as the area behind the bullet increases...as the bullet moves farther from ground zero.
The two...objects in motion tend to remain in motion, and fight acceleration less vigorously...and the falling pressure curve...tend to balance out and cancel the increase in "push" in the opposite direction.

I can't prove it mathematically...though I'm sure that someone can...but I'm gonna say that the increase in barrel length would result in an imperceptible
increase in recoil acceleration, assuming equal gun weight/mass. Measureable with the right instruments...but not with a "Seat of the Pants" calculation.

Check...

 

[Owen]

Tuner said

Remember that bullet movement is the initiator, and bullet acceleration is an important player. i.e. The harder that you try to move something, the more it resists being moved, and the more force is required TO get it moving. Conversely...Once you GET it moving, the less force it requires to KEEP it moving.

Resistance to acceleration is called mass. The mass of the bullet is constant, and the mass of the gun is constant. In other words, you are mistaken. You are confusing Newton's laws and static friction I think.

The potential increase in recoil from a longer barrel isn't because of the increased time in the barrel, but because of the increased velociy of the bullet. However, increasing the length of the barrel also increases the mass of the gun, and moment of inertia of the gun, which tends to reduce felt recoil.

What we are interested in here is the maximum velocity of the bullet in the barrel, which typically occurs at the muzzle. In a rifle, the powder charge is often a major fraction of the the bullet weight. (eg .30-06 with a 150 grain bullet, will often have a powder charge around 40 grains), so we need to include that too. Assuming half the powder charge has the same velocity as the bullet is probably a good estimation.

Of course, if the barrel is long enough, the bullet will stop in the barrel, resulting in the gun jerking forward after it slams back.

 

[1911Tuner]

Confusion

owen wrote:

>You are confusing Newton's laws and static friction I think.<
************

Probably... When they studied physics in high school, I was studyin' Bobbie-Sue or Leann, or somethin' related...

But on the point of increased recoil because of increased bullet velocity...We'll have to agree to disagree. Not arguing that it DOESN'T
increase it. Everything means something. It just won't increase it enough for
our hands to feel the difference...assuming equal weight guns and identical ammo.

I own a pair of Ruger M-77s...both in .308 caliber. (Actually, I own several .308 M-77s.) One is an RSI International with an 18-inch barrel. The other is a sporter with a 22-inch barrel. Both rifles weigh within 4 ounces of each other. Firing identical ammunition, the velocities are about 125-130 fps apart. I can't tell the difference, and it's not likely that anyone else can.
Measure free recoil with a device that'll provide numbers and fractions thereof...sure. But any practical difference between the two...Nope.


On static friction...it works a lot like mass and inertial resistance to acceleration, methinks. While scootin' a heavy box across a garage floor, it takes more oomph to get it started than it does to keep it goin'. Back to the bullet's frictional and inertial resistance to acceleration. Once it's movin', it takes less force to keep it movin' and less to accelerate it an additional 200 fps than it took to get it up to the first 200 fps. Less force forward...less force backward. It balances out.

Now...fire a heavy bullet at 2500 fps and a light one at 3,000...each round with identical peak pressures, and you can feel it. The heavy, slow bullet exerts more of a long push, while the light one is more of a quick slap. One moves the shooter more while the other one hurts his shoulder more.

Where's John at?

 

[JohnKSa]

But on the point of increased recoil because of increased bullet velocity...We'll have to agree to disagree. Not arguing that it DOESN'T increase it. Everything means something. It just won't increase it enough for our hands to feel the difference...assuming equal weight guns and identical ammo.

By the time you get to the end of this paragraph, we're getting pretty close to being on the same page.

I think that a 12% increase in recoil velocity (from your example) will be noticeable to some if not all. However, admittedly, that was an extreme (and therefore unlikely, IMO) case.

I don't think that you can categorically say that there will be no felt difference, but I think it is definitely safe to say that in most non-extreme (reasonable) scenarios that the practical difference will be minimal and probably not detectable by the shooter. Particularly when you consider that increasing the length of the barrel is likely to increase the weight of the gun by some significant amount. It's certainly possible that the recoil velocity could actually be reduced if there's enough weight increase.

This is a bit of digression, but muzzle flip is a different story since that's not so much a function of the weight of the gun as it is a function of torque and recoil momentum. So you could actually end up with reduced recoil (due to the added weight from a longer barrel totally counteracting the effect of increased recoil momentum) but at the same time have more muzzle flip due to the added recoil momentum applying more torque to the gun.

 

[1911Tuner]

Digression

Yep. The only way to put it to the test is to find two identical rifles with unequal barrel lengths...like my Rugers. Add weight to the lighter, shorter rifle to equalize that part of the equation...and have several people of varying body mass test-fire'em both and take a poll.

My bet is that a blindfolded, back-to-back test result will be "Inconclusive."

Come on up and see us, John! The weather will soon be -er.

 

[JohnKSa]

I'd be more interested in the results from pistols.

I have a 6" and a 4" GP100, but I don't think that's enough barrel difference. What would be perfect is to find a couple of the New Model Super Blackhawks, one with a 4 5/8" bbl and one with a 10.5" bbl. That would come very close to your earlier example. Plus, with a pistol, we could get some muzzle flip impressions as well as felt recoil opinions.

Come on up and see us, John!

Well, while I'm not sure I'm confident enough to bet on the results of the test, you can be confident enough to bet that if I ever make it to North Carolina I'll look you up. Even if it's just to get a chance to complain about the coffee.

 

[1911Tuner]

Test

John, because of the way that muzzle flip behaves in short-barrelled revolvers, I don't know that any handgun would be a good way to test it...especially the plow-handled .44 Blackhawk and they way they roll and twist. I'd think that would tend to be the "Grandstand" recoil and detract from any other input that you might get. I'd also be inclined to believe that
a pistol-grade powder...even a slow-burner like 296 or H-110...would be too quick to generate enough extra push after the punch to catch up with the
gun's established rearward momentum before the bullet broke free.

Think of it like a prize fighter who just caught his opponent coming off the ropes with a hard, straight right. The followthrough may rock him back a little further, but it's the sudden jolt that turns off his lights and buckles his knees. He drops so fast that the push doesn't really have time to affect him.

A rifle on a sliding fixture...a rifle on a rail...with a frictional brake would probably be the most conclusive. The slower burning rate of the powder
would peak later and hold the peak longer. Running the tests with different powders may also shed some light.

 

[1911Tuner]

Almost Forgot!

The one thing that I forgot...and there's no excuse for it, since it's related to the description of how the locked breech/recoil operated autopistol locks...
but a factor that hasn't been plugged in yet is the bullet's effect as it moves forward in the barrel.

The bullet is a tight fit. Try to drive one through with a hammer and a dowel rod to see just how tight it is. While the bullet is passing through the bore, that frictional resistance is causing the bullet to pull the whole gun forward with it...and it continues to pull for as long as it's there and and moving.

I remembered a slow-motion video that I watched once...of a 1911 firing a round to illustrate that the slide moves before bullet exit. The one thing that caught my eye was that the gun made a very slight, quick pitch forward just as the blowby gasses exited the muzzle ahead of the bullet. Too fast to have been the shooter anticipating recoil and pushing on the gun, it struck me that the gun was being pulled forward at the same time that it was recoiling backward, and actually began just ahead of the rearward movement. I'd venture a guess that if one could magically eliminate the rearward recoil during fire, that the gun would literally "kick" forward. Like pulling a bullet through the muzzle at normal speed, rather than pushing it from behind...

Would this forward pull cancel out the effects of the push that comes after the initial punch? It would seem so. Force in one direction equals force in the other. I'll leave it to the rocket scientists amongst us to make a call. When the teacher said that pies were square, he lost me.

 

[Owen]

Your correct tuner, the berrel gets pulled forward by the friction of the bullet.

As a thought experiment, pretend you have a revolver, with the barrel just loosely pressed into the frame, rather than threaded...

 

[1911Tuner]

Thought

owen wrote:

>>As a thought experiment, pretend you have a revolver, with the barrel just loosely pressed into the frame, rather than threaded...<<
***********

Already have. I've used the following to try and convince several people that the barrel in a recoil-operated autopistol is pulled rearward by the slide rather than "recoiling" and driving the slide:

Hypothetically, freestand a barrel on the ground with a round chambered. If the round fires, will the barrel press back against the ground...or will it be propelled skyward with the bullet?

My question is: Would the pull cancel out the equal and opposite push during bullet acceleration after the impulse? I think so. Firing a steady diet of magnum ammunition in a K-Frame Smith & Wesson...or any revolver...will cause the topstrap to stretch due to the barrel and frame being yanked in opposite directions.
If high-grade ordnance steel can actually be stretched by the tensile stresses, how can it NOT strike a balance. Is this the "Balanced Thrust Vector" that Kuhnhausen mistakenly used to describe the recoil function of the 1911? It is, methinks...

 

[wbond]

1911Tuner, I agree, but think the longer barrel and/or slide may help reduce recoil.

Quoting Tuner: Shield...No. Recoil isn't dependent on barrel length. As Vern noted, most of it occurs at ignition...Impulse. Although the bullet dwell time in the barrel will add a bit of push after the initial impulse, the effect is minimal in comparison to the sudden jolt when the round fires.

Wbond: Turner, I agree with what you said just based on my experiences and also common sense. However, I have personally experienced that recoil seems a bit less harsh to me with a longer barrel, but does have more push. i.e. - a longer barrel seems to have less punch and more push, which is easier on my hand. I think the extra barrel and/or slide length-weight may help tame the initial impulse. I've noticed this in autos and revolvers.

The punch (initial impulse) hurts my arthritic hand. The push (bullet going down longer barrel) does not hurt me.

 

[1911Tuner]

Recoil

Howdy wbond,

The longer barrels of handguns do tame the sharpness of recoil, but it's more a function of the extra weight, and the fact that the greater weight out front reduces muzzle flip. What we're trying to determine is how much more push
the movement of the bullet has on the recoil after the initial impulse, since the bullet is causing an equal and opposite effect for as long as it's in the barrel and moving. And the latest question is: Is that "Push after the Punch"
effectively cancelled out by the bullet pulling the barrel foward as it's forced through under high frictional forces...A "Balanced Thrust Vector?"

I'm in the camp that feels that the initial impulse is pretty much all that we can feel, and that the "afterburner" effect provides little, if any additional recoil...especially in handguns...due to the propellant's quick pressure peak and rapid pressure drop after the peak as compared to rifles and the slower-burning powders used.

A thought...even with centerfire rifles: The case shoulder would also tend to
pull the gun forward as pressure accelerates the bullet after the impulse. Notice how rifles often experience case stretching ahead of the web, and incipient head separation...due to the case becoming "frozen" to the chamber
and the head area driven backward toward the breechblock...the face of the bolt. This is something that doesn't occur with straight-walled pistol cases unless pressures are completely over the top, and even then, the whole case backs out first. The shoulder of the bottlenecked case provides a place for the pressures to impose force in the forward direction. This probably explains why we don't get the same recoil from a round like the .357 Sig that we do with the .357 Magnum, even with very similar pressures and velocities.

What say you, John and owen? Do the physics bear out the theory?

 

[usp9]

Slitting already split hairs

You guys are telling me you can tell the difference in the recoil in the first half of the barrel from the recoil in the second half of the barrel? The entire event occurs in about 1/4000th of a second. Equal and opposite are at work, but the variables involved are many, and only some involve the gun itself. Many, many more involve your grip style, strength, torque, powder burn time, etc, etc, and on and on.

You are splitting hairs already split IMO.

 

[1911Tuner]

Splittin' Hair

usp9...Exactly. If there's a difference, you ain't gonna have time to feel it.

All we're tryin' to do at this point is determine if there really IS a (measureable) difference...

 

[JohnKSa]

There is definitely a measureable difference assuming that the guns are very similar in weight. The science behind it is well-accepted and is not complicated or confusing. I thought we were arguing about whether or not a shooter would be able to DETECT the difference by the feel.

 

[jungle]

Velocity of ejecta runs about 4000-4700 FPS.

Given pistols of equal weight, action type will have a negligable effect on velocity or free recoil. Ammunition variations will be larger.

Recoil will increase with velocity given equal weight guns and projectiles. Longer barrels usually produce more velocity.

Barrel friction will not pull a gun forward, it is a much smaller component than recoil energy and is indeed swallowed whole when one considers muzzle velocity in a momentum equation.

 

[1911Tuner]

re:

LOL...We are, John. Then that forward yank from bullet friction got involved.

Jungle wrote:

Barrel friction will not pull a gun forward, it is a much smaller component than recoil energy and is indeed swallowed whole when one considers muzzle velocity in a momentum equation.

If bullet to barrel friction will pull a barrel forward hard enough to stretch the topstrap of a revolver...some revolvers within 200 rounds given hot enough ammo... I'd say that it's a fairly sizeable component.

I won't argue with the velocity of the escaping gasses. Don't know what it is.
But...okay. a 5-grain bullet at 4,000 fps. Half the recoil impetus of a .22 Stinger fired in a small revolver. Detectable...but we still can't ignore the
bullet to barrel friction. Does it effectively cancel out the "Push after the Punch?

 

[usp9]

jungle said;

Velocity of ejecta runs about 4000-4700 FPS.

Given pistols of equal weight, action type will have a negligable effect on velocity or free recoil. Ammunition variations will be larger.

Recoil will increase with velocity given equal weight guns and projectiles. Longer barrels usually produce more velocity.

Barrel friction will not pull a gun forward, it is a much smaller component than recoil energy and is indeed swallowed whole when one considers muzzle velocity in a momentum equation.

Yes. I agree with you completely.
Some of you are forgetting basic physics and gasses. When a round is fired there is NO impulse. I repeat, NO impulse. The pressure is caused by the burning of powder, creating a build up of gas, which lasts until the projectile has exited the barrel. If you want to call that time frame an impulse, I won't argue, but differenciating between rear of the barrel and front of the barrel is pointless. The point is, the projectile is constantly accelerating as the pressure BUILDS...not slows or decreases.

Recoil is determined by the amount of energy imparted to that projectile. The longer the barrel,,,the higher the velocity...thus more energy imparted. Recoil begins at primer burn and continues through till the round exits. Why...because that's how long the force is exerted. The only mitigating factor here is the added weight, if any, of a longer barrel, and the increase in inert mass to be moved.

Barrel friction, while a factor of degrading energy, is certainly a minimal force when compared to the energy imparted to the projectile. This is evidenced by the difference in muzzle velocity of traditional barrels Vs. Polygonal barrels, but as stated, there is probably more variance in powder quality conrol than gained by barrel design. Does that force stretch steel? I don't know. I quit using revolvers a long time ago when one failed me. Not many revolvers have a blowback slide anyway.

Barrel / breech/ linkage or action type has almost no effect on recoil. The formula is as always energy in equals energy out. What you actually feel is the combined result of all the springs, bushings, ergomonics, grip, sweat, muscle, adrenaline, and a thousand other factors. Sometimes the answer is : What feels good to you?

 

[jungle]

Friction accounts for about 10% of total energy in firing a round. The example of topstrap stretching is more likely caused by bullets yawing as they exit the cylinder and having less than optimal entry into the forcing cone.
After all we don't see pistol barrels stretching after 100,000 plus rounds.

When we compute recoil, muzzle velocity is used and this accounts for any frictional loss. It is not uncommon to see a squib drive a bullet clear of a barrel with just a primer and or a grain or two of powder.

Here is how the energy of a .30-06 cartridge was broken down by Army Ordnance in 1929:

Heat to case 131 calories
Kinetic energy of bullet 885 calories
Kinetic energy of gases 569 calories
Heat to barrel 680 calories
Heat to gases 599 calories
Heat generated by friction 212 calories

 

[1911Tuner]

Impulse

usp9 wrote:

>>Some of you are forgetting basic physics and gasses. When a round is fired there is NO impulse. I repeat, NO impulse. The pressure is caused by the burning of powder, creating a build up of gas, which lasts until the projectile has exited the barrel.<<
******************

No argument there...but I'd still estimate that fully 95% of the recoil generated occurs before the bullet has move a half-inch. Call it impulse...Call it fast pressure peak...There it is.

I recently ran a test of the theory in which I reamed the rifling out of an old 1911 barrel all the way to the chamber shoulder...opened the ID up to nearly a half-inch...and fired several rounds in the barrel. The slide cycled. The empty case ejected smartly...and the slide locked on the empty magazine. Nothing was changed in order to insure full slide travel. The recoil spring was 16 pounds. The mainspring was 23 pounds. Felt recoil was reduced by a small degree...barely detectable...which was one reason that I fired several rounds. Even the round's report was unchanged. It felt and sounded like a normal round fired in a normal barrel.

I was partly trying to determine how fast the recoil occurred...and trying to see just how much difference in felt recoil there was. I finally came to the conclusion that the small difference likely came from the reduction in the quick pressure rise at the outset. Because the bullet didn't hit the resistance of the leade and rifling as soon as it moved, the pressures didn't spike as quickly, nor hit full pressure the way they would have had the barrel sealed off the gas escape.

With the bore .050 inch over bullet diameter, and almost .025 inch of clearance around the circumference of the bullet as it made the trip through the barrel, I'd estimate that the muzzle velocity was well below 600 fps. I never got a chance to chronograph it, being a little nervous about having a 5-inch unrifled barrel attached to a gun...so I destroyed the barrel shortly after the test.

Stretch due to bullet yaw...

Not sure that would be the determining factor, jungle. The bullet's friction in pulling the barrel of a locked-breech semi-auto is half of the locking of the barrel and slide. I've seen dozens of locking lugs deformed
toward the rear, and flanged at the top due to pressures pushing the barrel in one direction and the slide in the other. Ordnance steel is pretty tough. It would require serious forces to mash a locking lug to the point that it flanges like that. Of course, other factors make it more
likely or make it occur earlier...Barrel to slide endplay is one. If the lugs get a running start before engaging, the damage occurs earlier and with less pressure required...but it still happens even with tighter clearances.

 

[jungle]

As to barrel travel, the projectiles rate of acceleration is greatest as pressure is highest and although pressure drops as it moves down the barrel acceleration continues until barrel exit, although the rate of acceleration is slower.
Regardless of this, recoil is measured based on muzzle velocity and not pressure.

It is the two components of mass and velocity that constitute momentum, which we refer to as recoil in guns. This applies to spearguns, bows, and any other device that sends a mass out at some velocity.

The lugs flanging on 1911s has a lot to do with the running start/clearance and the movement that occurs at pressure peak as the slide and barrel try to drive apart.

Old Fuff is the revolver expert, perhaps he has a comment on topstrap stretching. As I remember, S&W put it down to bullet yaw on cylinder exit and this was made worse with certain loadings. Perhaps there was also an issue with cylinder timing.

 

[1911Tuner]

re:

Quotes:

>As to barrel travel, the projectiles rate of acceleration is greatest as pressure is highest<
******************

No argument there, either. But the pressure peaks fast in a handgun...especially in an autopistol, due to the quick powder rates used.
The fact remains that in my experiment, the felt recoil was pretty much unchanged and the slide made the full trip...without any rifling in the barrel at all, and with .025 inch per side of gas escape. Given that, I have to believe that very little felt recoil is dependent on muzzle velocity OR barrel length.

When the results of the experiment don't jive with the theory...go with the results.
***********************

And:

>The lugs flanging on 1911s has a lot to do with the running start/clearance and the movement that occurs at pressure peak as the slide and barrel try to drive apart.<
***************

No argument there either...but it still occurs when there is no running start.
It just takes longer.

A point that you may not be aware of is the old ordnance method for equalizing locking lugs in horizontal engagement. The first two lugs were fitted, and the third was left kissing about .002 inch of air. The guns were then fired with proof-level ammo a few times in order to deform the first two and bring the third into play...and the flanging stoned off. I still do that on some pistols, and it works well. A zero-clearance fit on the first two lugs...followed by pressure-equalizing of the third...creates 2 or 3 thousandths of clearance in the barrel fit. I like a bit of clearance in a carry or duty gun, so I use this method, since that's my venue...and because it's a little faster than fitting for all three lugs. Sometimes, I do it with standard-pressure ammo, though. Usually takes about 2,000 rounds.

 

[jungle]

Let's keep in mind that felt recoil is highly variable and dependent on the individual. There really can be no argument that a given pistol will recoil with the same force with a 230 gr bullet at 830 FPS and one moving out at 600 FPS. There may be enough energy to operate the pistol with both loads, but it is a physical absolute that recoil will be higher with the higher velocity.

I read about the ordnance style seating of the lugs by proof load in KII, I hope you aren't using proof loads to get that same effect. I think a few hundred rounds of firing would have the same effect.