Home Forums Hunting & Shooting Ask The Gunwriters Recoil and short barrels

Having broken down a number of short mag factory rounds, I've found that they're stuff with about 5 grains (on average) less powder than "long" magnums. This is indeed less powder, but not much less.

Everything else being equal, short mag rifles weigh 3-4 ounces less than long action rifles. That's how much weight is saved by going to a short action.

Now, some short mag rifles do weigh considerably less--but only because the stock and barrels are also slimmed down, not because of any vast weight savings in action weight.

After shooting a whole pile of short mag rifles, my impression is that they kick very similarly to long mag rifles with the same ballistics. The slightly smaller amount of powder is just about balanced out by the slight weight savings in the action.

The problem with everything we've been discussing is that almost all recoil formulas use a constant for muzzle pressure. My own modest attempt, a decade ago, gave different rocket effect values to different capacity cartridges. (These values were not grabbed out of the air, but partly derived from my own experiments with free-recoiling rifles.)

But in an ideal formula we'd also have to give different values to different barrel lengths. We'd also probably have to assign the stock design some sort of index number. So far all of this has eluded us, so any mathematical approximations of recoil remain just that: approximations.

MD

Well folks, I offer the following synopsis taken from "Recoil for Dummies":

Big, loud - kick hard.
Small, quiet - not kick so hard.



And that's all you need to know! <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

And the answer is����..

Slightly less actual recoil with a shorter barrel (as the only change). Slightly to substantially more felt recoil depending on the weight (mass for purists) removed and the change in rifles center of gravity.

Recoil force acts with a moment around a point of contact with your shoulder. By cutting a barrel you are moving the firearms balance point rearward. This has the effect of causing more muzzle lift which is perceived as more recoil. An example of this moment is shown in stock design. More drop - equals more moment arm in recoils favor - equals more muzzle lift and therefore more felt recoil.

Add to this the noise factor of the shorter barrel, again perceived or subjective and not actual force or energy the shooters body has to absorb.

Gun powder is the only working substance we are dealing with. It is the sole creator of energy, force, momentum, whatever that is known as recoil. The bullet moving forward is as equal a result of this combustion as the firearm moving rearward. Bullet velocity is useful only to help mathematically model recoil. You must likewise factor in the powder because the bullet and powder mass move together in the same direction. No one in this thread ever suggested bullet momentum was the only component in calculated recoil.

A shorter barrel doesn�t make anything more efficient, doesn�t create more energy, and doesn�t raise pressures. You can�t have more recoil without adding something new into the equation that generates force.

Rocket effect, please! I suppose the rocket site is getting the shorter rocket engine question so it�s understandable. The rocket effect is the changing center of gravity and resultant moment arm effect and nothing else.

I rest my case...

Could somebody pull up the "Rocket Effect" article and email it to me or something. Or at the least, post the basic premise of the article in a chart about case capacity. Thanks, it was before my time of reading Wolfe pubs.

I'm going to quote "Hather's Notebook" Chapter XII, "Third Element of Recoil," and then I'm done with this thread.
"This is that part of the recoil of the gun that is caused by the muzzle blast produced when the bullet leaves and the pent up gases are free to expand into the atmospheres. The gases then rush out of the muzzle at high velocity, and give the gun the same kind of push that propels a rocket or a jet plane. In Springfield rifles, or the Garand either for that matter, the pressure of the gas at the muzzle when the bullet leaves may be anywhere from less than 3000 pounds per square inch to well over twelve thousand, depending on varius factors, such, as for example, the length of the barrel; the granulation of the powder and its composition; whether it is quick burning or progressive burning, etc.
"With a high muzzle pressure, the rocket-like thrust of the expanding gas is much greater than with a low muzzle pressure, and the recoil is correspondingly intensified. Shortening the barrel always results in higher muzzle pressure, other things being equal, and therefore increases recoil, sometimes very noticeably."
As I end, note that Hatcher and I constantly qualify "all other factors being equal" which means any mass lost to cutting off a barrel is added back to the mass of the gun for no net loss of mass.

Indeed it does, and quite dramatically, at the point where it matters for recoil: At the moment the bullet leaves the muzzle.



In fact, it makes the rifle less efficient. Same energy (powder charge) input, less bullet kinetic energy output. That lost energy goes somewhere. The somewhere that it goes is the waste energy that the gas dumps as it exits, increasing recoil.

Everyone who shoots knows that gases expell from the barrel; Leaves kick up, grass blows over etc.

Nobody, and certainly not me, could make a good argument that this does not give rocket-like thrust back toward the shooter. I understand that this is the rocket effect that is being used in this discussion.

A buddy of mine always reminds me " If it's in print it must be true".

I'm sorry but I must disagree with Mr. Hatcher. I'm OK right up to where he states that cutting a barrel (only) increases recoil.

Please don't try to convince me that a barrel triming can add energy to a closed system because then I'd want to put it in my tank, gas prices being as high as they are.

You know that you can come to a logical conclusion and still be wrong don't you? I't's when logic is based on faulty reasoning. I've read this thread endlessly and I know where the mistake in reasoning lies. It's time for y'all to do the same.

Nobody has said anything remotely resembling that.

Scott, and Hatcher, are correct: From the simple gas laws, as the volume between the bullet and the bolt face increases, the pressure of the gas will drop. The farther the bullet travels down the barrel, the greater the volume becomes, and the closer the gas behind it gets to atmospheric pressure. The closer the gas is to atmosphere when the bullet exits, the less rocket effect recoil will be generated.

Shorter barrels produce more rocket effect recoil.

I had gas once and it did indeed raise the pressure.

what if the barrel was so long that the bullet stopped before it exited the barrel, would there be any recoil.. discounting the 2 ton barrel weight. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" /> <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

After reading much of the thread, I have one question: What was the origninal question? <img src="/ubbthreads/images/graemlins/help.gif" alt="" />

Uh, go shoot a short bbl gun and a long bbl gun...see which one kicks harder. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

We still have not solved the conflict implied by the original question:

Does the increased muzzle pressure of a shorter barrel outweigh the decreased recoil caused by the lower muzzle velocity of the bullet?

Shorten a barrel 4 inches and muzzle velocity is generally decreased at least 100 fps. This, by itself, reduces recoil.

MD

Thank you Mule Deer. You said long ago all that needed saying.

It would seem so at first blush, but I seriously doubt that it matters much.

All other factors equal, the recoil for an 18" barrel and a 24" barrel will be identical, up to the 18" point. Past 18", the 24" bullet is getting relatively little acceleration, and the additional recoil force generated will be relatively small. F=ma, and all that.

However, that 6" difference makes a huge difference in the gas pressure in the barrel at the moment the bullet uncorks it. That in turn makes a large difference in the recoil force generated by the rocket effect.

It has been a fun discussion, but it is time to take .280Rem's advice, and just do the measurements. I've located a device that will measure the force of recoil vs. time, and I have two 6.5x55's that weigh about the same, one with a 29" barrel, and the other with a heavy 24" barrel and a scope. They can shoot the same ammunition, and can be trimmed to have the same weight. If I can trim my little Rossi 20 ga. to weigh the same as my wife's 20 ga., I can get a second comparison. The project will have to wait until the snow clears, but we will soon have real data.

I took up shooting, because I enjoyed it as a teenager, and I needed something to get me out of the house, and off the computer more. Something has somehow gone horribly wrong...

sometimes there's more to it than barrel length... I have a Lee Enfield No. 5 (jungle carbine) 18.5" barrel... kicks noticeably more than a number 4.... I suspect a big part of the reason is that the substantial muzzle blast is converted to recoil by the rocket-cone shaped "flash eliminator" on the end of the barrel. (?)

I'd guess the "rocket effect" is in play somewhat with a normal crown, but is multiplied several times if you put a cone on the end of the barrel.

A couple years back I asked on a Lee Enfield forum for someone to remove their flash eliminator and test the effect on recoil. I didn't want to un-pin (monkey with) mine. Funny... didn't get any takers <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

quote]

I took up shooting, because I enjoyed it as a teenager, and I needed something to get me out of the house, and off the computer more. Something has somehow gone horribly wrong... [/quote]

The birthday given in your profile is 11/29. There were no computers when you were a teenager. <img src="/ubbthreads/images/graemlins/blush.gif" alt="" />

When I was a teenager, I was doing what a good lad should do, out abating the jackrabbit nuisance at every opportunity. The computer thing came along later... probably to my detriment. I had a Tektronix 4051 in (what??) about 1978-79. That was the original graphics capable computer.

Thank you Mule Deer, for this reminder :

Indeed the question is not solved in principle but there has been progress and a good debate. I hope that it will continue until fruition, so that we all know the answer for sure before the discussion ends. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Thank you to all previous and future contributors to this thread.

That would be very interesting Denton.

Real and good data always help to separate facts from hypotheses... <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

I was just working on this one.

The three main reasons for recoil differances are;

(1) Mass at rest tends to stay at rest. A 10lb rifle far out weighs a 180gr bullet. A 7lb rifle % wise is much lighter. Thus a 7lb rifle will move easier.

(2) Muzzle Blast. For example; If you take a air compresser that compresses air to 90psi you will have 90psi at the tank. Hook up a hose with a 3/8"ID that is 10' long and you will have some pressure loss. Hook up a hose 30' long and you will have a large pressure loss do to the volume of air that can get into the 3/8" hose for 30'. It is another matter of %age. Now let the air go through the hose and let it go. The 10' hose will whip much faster. If you have a blower end for your hose hook it up. If it has two holes on the sides near the end put tape over the hole. The hole are a venturi and will work as a muzzle break. Pump the air on and off with the 10' and 30' hose. Now remember we are not pushing somthing down the hose, this is just expanding air.

(3) A short barrel has less time to burn all the propellent and power that is unburned 1/2 the way down the barrel is just going to be expanding as it leaves the barrel and add to recoil.

I just read a article about short fat verses long thin rifle cartridges and there efficiency. One of the things it hit on was using a "elliptical sholder to focuses primer blast" back at the base of the bullet area. This is somthing I have hinted at before and I'm very intrested in. I see it more like the double spark in high performance motors for a more efficient burn.