HitorMiss said:
Teddy, Big Red.
You believe this to a be a failure of the rifle to deal with the gas regulations, as in not being dissipated properly and stressing the action beyond what was thought of during development?
I ask because I am no expert and information is power were I to run into the same issue.
Short barrel gas operated Semi Auto, or Full Auto rifles typically have more severe pressure curves than their longer counterparts. This is due to the gas ports being closer to the chamber, and thus the fired cartridge, than on the full length version. This can be an advantage in rifles with dwell time issues (dwell time is the time between when the bullet passes the gas port, and when it leaves the barrel. Typically, the longer the dwell time, the more reliable the rifle. Though this rule, is countered by the law of diminishing returns. There are exceptions to this rule as well. The M-1 Garand, which has it's gas port at the muzzle, springs immediately to mind.) such as the SIG 552/Swiss Arms Commando or 10, 10.5, 11 inch AR-15/M-16 series rifles. The higher pressure will help get gas down the tube, and cycle the rifle.
But it also means that Short Barreled Rifles put more stress on their working parts because due to that higher pressure, they cycle much more quickly and violently. This is because not only does the gas have more pressure but also less distance to travel, down the barrel and back down the gas tube as well. This will effect direct gas rifles more significantly than rifles that use a piston/operating rod mechanism. Many designers incorporate heavier components in the shorter rifles to counteract this, ie; the shorter AR/M-16 series will typically use a heavier buffer than the full length versions. This of course, takes more energy to move and slows down the action, reducing cyclic rate on full auto versions, and reducing the stress placed on the moving bits.
Now I don't have a scale, or a comparable 550/551 bolt carrier, but I would be that the 552 bolt carrier, due to the way it's constructed, is actually lighter than the longer version's bolt carriers. That combined with the higher gas pressures has me betting that the 552s are beating themselves to death. It's causing a lot consternation among our shooters, that some of them have told me they're contemplating carrying their AKs again, instead of the SIGs. Incidentally, our company recently stopped buying the SIGs and started purchasing the Zastava M-21. A Serbian built 5.56 AK. But I think that was more to do with cost than anything.
HitorMiss, I hope this helps.