Semi auto vs bolt action recoil -- is there really a difference?

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So today I had my M1 Garand out, since it was a nice sunny day out and perfect to do some shooting with it. I was really studying and marveling how it works, and it got me thinking, because of the way I understand it works, shouldn't it have recoil about equal to a bolt action 30-06 that is similar in weight?

If I'm correct, doesn't all of a firearm's recoil happen while the bullet is still in the barrel? Because of Newton's third law, as long as the bullet is providing resistance going down the barrel, the expanding gas will exert an equal amount of force in the opposite direction, but once the bullet leaves the barrel, there is no resistance and any unburned powder freely escapes. The reason I bring that up is because as I understand it, the bolt on a semi auto is designed to stay locked shut while the bullet is still traveling down the barrel, therefore all of the recoil energy is going straight into the locked bolt and into your shoulder, NOT being absorbed by the spring. So correct me if I'm wrong in any of my thinking, but if all of the recoil action happens when the bullet is still in the barrel, and the action doesn't cycle until the bullet has left, doesn't that mean the entire recoil event happens before the spring can absorb any of it, therefore causing similar recoil to a bolt action?
 
In theory, yes there is a difference in the recoil composition. But you could make an argument as you did above the total energy imparted to the weapon and shooter is the same. But other factors come into play.
If you look at recoil as the impulse plus a 'push', a bolt that is moving will slow down some if the impulse into a slower push.
 
After shooting a couple of bolt action for the past few years, an auto loader chamber the same as a bolt action is down right mild. Of course that's just an impression not lab comfirmed data.
 
Gas operated autoloaders tap off some portion of the "push" to
operate the action.

Everything else (fit, ammo etc) being equal,all autoloaders will
FEEL like they have less recoil.

The total rearward impulse may be the same for all actions---
no matter how hard you try you can't cheat Newton--but
the subjective "feel" will be less on an auto-loader because the
impulse is spread out over a longer time.

You want to really see this in action, try firing a Solothurn 20mm.
Long recoil action---the whole process feels like it takes several
seconds. No real kick--just a weird L-O-N-G push. Still sets you
back a few inches, but small children could shoot it.
 
Gas operated autoloaders tap off some portion of the "push" to
operate the action.
Click to expand...

yes, and no...

all the push is still there, but some of it is redirected outside the bore. The push against the bolt, or op rod or piston, is still a rearward push (once it gets there) nothing is actually "lost".

But what changes is the feel, and what is delivered at any specific moment in time. Recoil feel is dependent on the total, over time.

A good example is to shoot a 12 ga pump and semi auto (same approx. weight) with the same shells. My experience is that the "fixed breech" pump will feel like it has more recoil than the semi auto with its moving parts.

The total delivered has to be the same (physics), but the pump gives it to you all at the same instant, while the semi gives it to you over a slightly longer period of time, and so feels like less of a jolt.
 
That's the right answer ! I used to have some info from HK .They were graphs ,vertical axis was force, horizontal was time. Area under the curve is recoil energy .That area for both curves was the same but clearly the maximum force was highest for the bolt action and occurred in a short time . The maximum force for the semi was lower but the time was longer.
Sharp punch vs soft push . The delayed blowback of the HK would be different from the other typical semis. I remember when I first got my HK P7 those that fired it said it was like shooting a 380 !:)
 
in the M1, since it's the gas in front of the bullet operating the piston, the recoil is the same. personally, I feel like my garand kicks more than my springfields ever did but now my M1917 kicks worse than my M1...


it varies from design to design.
 
One of the most vicious kicking rifles I shot is the straight grip M1903. I am of the opinion that the total recoil energy is the same, only little differences in weight, but the recoil is spread out over a bit more time in the Garand and it feels less harsh.

Given that whole event of projectile exit and bolt unlock occurs faster than human perception, felt recoil is very subjective.



 
While for the most part you are correct, not all fish are from the same species the semi-auto shown below is of a blow-back design and does not have a locking bolt. Impulse recoil is absorbed by the recoil spring as well as it has springs in the recoil pad on the back of the rifle.

Jim



This one carries a recoil spring and buffer as well as having some of the gas bleed off \at the gas port 2/3rds of the way down the barrel.



This one uses a Linear muzzle brake to bleed off gases and reduces recoil and muzzle rise.

 
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The recoil impulse is spread out over a longer time period with auto loaders.

Two cars can reach 60mph. One does it in 2 seconds, the other 8. Which will snap your head back more?

I can shoot my Garand for an hour with no issues. 5 rounds of 30-06 in a bolt and I'm done. Same goes for revolvers.
 
A certain amount of the soft recoil with a Garand is due to the semiauto gas action. A lot of the soft recoil with a Garand is due to the darn thing weighing 10 lbs.

BTW, recoil starts as soon as the bullet starts moving, but it continues after the bullet leaves the barrel. The expanding gasses push the rifle backwards like a jet engine. That's why muzzle brakes reduce recoil; they allow the gasses to exit sideways.
 
If I'm correct, doesn't all of a firearm's recoil happen while the bullet is still in the barrel? Because of Newton's third law, as long as the bullet is providing resistance going down the barrel, the expanding gas will exert an equal amount of force in the opposite direction, but once the bullet leaves the barrel, there is no resistance and any unburned powder freely escapes
Click to expand...

You are incorrect.

The first stage of recoil happens when the bullet is in the bore.

The second stage happens when the bullet leaves the bore, and like a champagne cork popping out lets the highly pressurized gas escape.

When a balloon is let go without being tied off, it flies away. If you knock the top off a pressurized gas cylinder laying on its side it will accelerate enough to punch through a brick wall.

Escaping pressurized gas is even how we launch rockets into space. Even in a complete vacuum rockets work just fine to provide thrust even though there "is nothing to push against" so to speak.

I hope this expands your understanding of the forces of recoil.

Jimro
 
I few months ago I had a chance to do a range session with some police officers. They were trying out a sample of the AA12 (fully auto 12ga). I am not sure how they do it but that thing kicks like a 22lr.

I am not sure why newtons laws of physics do not apply to this gun. I am sure there are videos online saying the same thing. Granted its a heavy gun but even that (to me at least) does not account for the low recoil. They were running full power buckshot.
 
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Thanks for the responses, I think Jimro explained it the best. I was under the impression that ALL of the recoil happened when the bullet was still inside the barrel, but your explanation makes sense. So I guess indeed the action of a semi auto like the M1 would absorb some, also like natman said, the thing does weigh nearly 10 pounds, it makes the mosin nagant feel light.

I've seen some videos on the AA12, I'm also quite amazed at how much it's able to tame 12 gauge shells of any kind. I know of course it has to do with the recoil absorbing mechanism, just don't know how it works exactly.
 
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