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Member
Correct IMO. I have a .223 bolt gun that weighs the same or less than my AR’s and the “felt recoil” is substantially less than any of them. The “felt recoil” from most AR’s is more a result of 1 lb of steel slamming to a stop into your shoulder than from propelling the 55 gr bullet forward.Originally Posted by markm
Yes, I know all about the physics, that it can’t actually create more energy than the cartridge firing produces, etc, but that’s not how it comes across.
Senior Member
Recoil energy and felt recoil are different. If you bungee cord both my 18" 223 bolt rifle and my 18" Rifle gas AR on a little red wagon and fire the same round in each, the wagon will move the same distance.
Shooting each at the range feels entirely different due to a number of factors. Generally speaking, semi autos shoot "softer" because the recoil impulse is spread over a longer period.
A well set-up AR shoots "softer" because the cyclic rate is slower and recoil is, again, spread over a longer period. An overgassed AR with a too-light buffer and weak recoil spring has a shorter recoil cycle and "harsher" recoil.
The OP asked about recoil for a 6x45 70 gr @ 3000 fps compared to a M4 (I assume 5.56). If the OP shoots the 6x45 and a 5.56 (69 gr @ 3000 fps) from a similar firearm, there is no practical difference.
Andy
Last edited by AndyLate; 01-31-21 at 09:43.
Member
I don't think this can be true because a spring will store some of that energy ("stealing it from the round") and then returns it back to the BCG going in the fwd direction. The energy absorbed by the spring and then returned back to a impact force as BCG slams into battery in opposite direction would cause the wagon to travel a lesser distance.
A bolt will always put more energy into the bullet vs a semi-auto? Why? Because the very point in time the back of the bullet passes the gas port there will be a PSI "drop" behind the bullet, thus a little energy is now in the gas system.
The diff may not be significant, but the two are different.
Last edited by DwayneZ; 01-31-21 at 22:18.
Member
Well I can say for sure that my first AR upper (a RRA overgassed 16” carbine system HBAR) had WAY more felt recoil than the lightweight 14.5” BCM middy that replaced it, despite the vast difference in weight, both shooting 55 gr. Wolf gold.
And when I dialed in the adjustable gas block on my 12” 6.5 Grendel, I did feel a difference from wide open to dialed in.
No difference in loads. Calculators are good for comparing theoretical differences in calibers, but for felt recoil, that’s got more to do with the rifle. A Limbsaver pad can reduce felt recoil, even if it’s just spreading the same energy over a longer period.
Industry Professional/Moderator
There's a lot more to recoil than can be quantified with a calculator.
Here's how it's really done:
Senior Member
No.
1) The spring pushes in both directions, it pushed the bolt forward, and the rest of the gun backwards. So, it does not "steal energy", it just borrows it, and returns it at a later time.
2) Where does the gas go? It goes into the cylinder and pushed the piston rearward into your shoulder via a spring.
The thought experiment described by Andy has been carried out many times and the results are always the same, the little wagon rolls back the same distance. It's been done with wagons, sleds, suspending them on strings, dropping them, anyway you can imagine. And, it always agrees with the calculations from the laws of conservation of momentum and conservation of energy.
People that think that recoil is different for different operating mechanisms are the same ones that think that a blow-forward gun is a reasonable idea.
Perceived recoil =/= recoil
Member
How is a bcg slamming fwd into battery any different than the energy of round blast hitting a muzzle brake?
In both cases some of the blast energy slams into the rifle barrel with a energy vector 180deg from recoil.
Sled tests of various brakes show us how the brakes reduce the recoil energy.
Member
A muzzle brake redirects mass which would otherwise have been forward momentum and which would have resulted in recoil if not redirected.
The BCG slamming backwards and then forward displaces the recoil in time but doesn’t increase or decrease it.
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Senior Member
Muzzle break reduces recoil because the recoil from the gas itself is reduced. It is 2 vectors (left and right) both 90dregrees to the recoil vector, so they cancel each other out
Everything about the bcg is inline with the bore. All the energy that the bcg slams home with has been put in the recoil direction the entire cycle time.
If you shoot an open bolt gun, you'd get it. The gun recoil before the round fires, resulting in high shots
Last edited by MegademiC; 02-01-21 at 13:42.
Member
Brakes allow the gas to change direction by way of resistance. The bore is say X axis. When the gas turns there is XY components of the forces, the Y's cancel but the X's on left and right side add up, and in this case it's all in same direction, thus pushing the barrel fwd some.
As far as the red wagon (sled) tests, it's not possible for two rifles of varying mass to move the same distance when using the exact same rounds. It's a MV=MV conservation equation.
A sliding BCG picks up some recoil energy, which is then returned back in opposite direction (identical to a brake). The timing of the events is obviously spread out over time.
This one is a good explanation of it.
https://www.chuckhawks.com/rifle_recoil.htm
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