Bolt vs bolt carrier mass ratio to predict reliability?

[briansmithwins]

The authors of this paper seem to think bolt to bolt carrier mass is a good predictor of a autoloading rifles reliability:

https://docs.google.com/open?id=0B09fZpC9S7gDU0RpanJDTXhCbWM

Dicussion is on page 71 of the above linked doc.

Did some weighing and here's what I've got so far:

SCAR 16S- 8.75:1
FS2000- 8.25:1
AR15*- 7.1:1
AK47- 4.9:1
SKS- 1.75:1

What say you about the whole idea? Anyone want to post numbers for a Garand, M1A, or other autoloaders?

BSW

*FA bolt carrier with 3 ounce carbine buffer.

 

[Kush]

No, it would depend on the area of the part of the bolt or gas piston that the gas is acting on, the combined weight of the bolt and bolt carrier, and the pressure of the gas acting on that area. Although the weight of the bolt carrier by itself would matter for the time it takes the gun to unlock and lowering it to much could make the gun dangerous, and raising it past a certain point could make it have to much inertia and not have the gas accelerate it enough to make the gun function reliably (although that could be fixed with having more gas pressure act on the bolt or gas piston).

 

[briansmithwins]

So, if I'm understanding the paper right, what they are saying is that for a given amount of energy that the bolt carrier possess, the bolt carrier has to expend some of its energy to unlock the stationary (from the frame of reference of the barrel-receiver) bolt. The bolt carrier has to lose energy to do this, since by the point the bolt is unlocking gas port pressures will have fallen to low to continue accelerating the bolt carrier.

The bolt can also be accelerated rearwards by residual bore pressure, since that doesn't drop to zero instantly, even after the bullet has left the bore.

If the bolt carrier weighs a lot more than the bolt the loss of momentum can be kept to a minimum. That momentum is what drives the action back to complete the extraction, cocking, and ejection part of the action cycle. Bolt carrier momentum is also what gets transferred to the recoil spring (and buffer if present) to power the return stroke of the action.

BSW

 

[Slamfire]

No text.