CleverNickname wrote:Cedar Park Dad wrote:
Additionally, how would the new piston driven AR types compare (S&W, Sig, Ruger for example)?
Piston AR15's are a hack that shouldn't exist. First, the AR15 BCG was not designed for being struck by an off-center force and the AR15 bolt was never meant to be dragged out of the locking lug area with the tail of the bolt forced downwards by the bolt carrier, dragging the top front and bottom rear portions of the bolt lugs along the barrel extension lugs. This causes uneven and unnecessary wear on the lugs, and contributes to premature parts breakage. Also, tilting carriers do cause wear to receiver extensions, which is worth mentioning, even if it is nowhere near as large of a problem as bolts tilting up under pressure, while rotating.
Second, the bolt is designed to have forward gas pressure pressing against the gas rings on the bolt, as the bolt carrier pulls back an unlocks. This provides an equalizing push on the rear of the bolt, and prevents grinding of the rear of the bolt lugs as the carrier moves back. On a piston rifle, there is no gas inside the bolt carrier, and thus no equalizing forward push. This leads to more off center, un-cushioned grinding of the bolt lugs, and premature parts breakage.
Third, the speed at which piston guns unlock is much faster than the speed at which DI guns unlock. This is why they mostly use heavier buffers, to slow the bolt carrier travel. The difference is measured in fractions of a second, but it is significant when dealing with gas pressure. DI guns are designed to unlock as gas fills the bolt carrier group, and provide time for the chamber pressure to drop. The gas piston guns unlock at the speed the rod strikes them, nearly instantaneously, with no cushion of gas pressing the bolt forward and provide the same sort of overzealous extraction that often rips brass, and violent cycling that we expect from a $600 overgassed DPMS. This too, is bad for all moving parts of the gun.
In short, don't get a gas-piston AR15. If you want a gas-piston rifle, there's plenty of other types of rifles out there that were designed from the ground up to use a piston; get one of those.
