
Originally Posted by
MistWolf
To make a gas driven rifle work properly, there are three things that need to be balanced out-
-Mass of the reciprocating parts
-Control of the gas flow including mass, velocity and pressure
-Spring compression rate and rate of relaxation
Change any one of these and the others will need to be adjusted to match.
Let's clear up a few misconceptions. First, the only reason a change in the mass of the reciprocating parts will change how much free recoil the firearm generates is because it changes the mass of the whole firearm, not because the mass of the reciprocating parts was changed.
Firing the same ammo at the same velocity, a firearm with greater mass has less free recoil than one with less mass. It doesn't matter where that mass is. If you were to lighten the carrier by 4 oz but added 4 oz to the barrel, the rifle will still generate the same free recoil because it still weighs the same. If you just add 4 oz to the barrel, the rifle has more mass and thus less free recoil. Will that recoil feel the same as would if those 4 ozs were added to the carrier instead? Probably not because a heavier carrier moving back and forth in the upper will feel differently than a lighter one.
badazz posted inaccurate information about springs. Will a spring relax faster when pushing less mass than it would pushing more mass? Definitely maybe. A spring pushing a good amount of mass will relax at a slower rate, but even when pushing no mass, it has a finite rate at which it relaxes. The more you lighten the load on the spring, the less gain in velocity. It's the law of diminishing returns.
In an AR, the spring pushes the BCG back into battery with energy that has been stored into it from the momentum of the BCG opening. The gas gets everything moving but after a short distance the gas is cut off and from there, the whole shebang is just coasting. Less mass in the BCG/buffer, the less momentum it has to compress the spring, the less momentum it has to compress the spring, the less energy the spring has stored. It's possible that the spring will not have enough speed or stored energy for reliable function.
A heavier reciprocating mass does not mean the rifle will have softer recoil. In fact, the greater the reciprocating mass, the more likely it will cause the muzzle to move off target while in motion. If the BCG/buffer were to account for 20% of the whole mass of the rifle, it will move the rifle around more than if it were only 10%. The trade off is that the lighter BCG/buffer has to move faster to load the rifle with the same energy- or use a stiffer spring. Note that a stiffer spring isn't always a faster spring.
A lighter BCG/buffer isn't more likely to bounce than a heavier one. There's more to it than velocity. What causes bounce is the carrier hitting the barrel extension in such a way that energy is reflection cause the two parts to bounce away from each other, like striking a hardened steel surface with a steel hammer. There's bounce. But strike that same hardened surface with a deadblow hammer designed to spread out the energy, it won't bounce at all, even if the deadblow weighed the same and strikes with the same velocity.
The JP low mass carrier can be made to run with the same reliability as a standard full auto carrier but the rest of the system has to be tuned to make it happen. 3 gun guys don't tune their rifles that way. They tune their rifles to run at the very edge of reliability with a certain ammo for the softest recoil and least movement of the muzzle from target. When everything is in balance, a "race gun" will work every time. But that balance is delicate and easily upset.
Bottom line is the rifle gas system with a 20 inch barrel, rifle spring and rifle buffer or A5 buffer is the most reliable and forgiving set up for an AR firing the 5.56x45. Everything else trades reliability for some other advantage such as a shorter package
Bookmarks