07-30-2011, 11:27 PM
Since the AR15 already has a pretty high cyclic rate for the reciprocating parts, cutting the carrier weight only increases bolt carrier velocity to the rear, which also increases the return-to-battery forward stroke velocity. It is hard on guns, sometimes beats the magazine spring, causing a failure to feed, and started when the SP1 was released by Colt for the civilian market in the early 1960's. The general consensus is that they didn't want to be seen as providing a rifle that would easily be made into a select-fire assault rifle, so the bolt carrier was shaved in the rear mass area underneath, where it normally would mirror the top rear carrier geometry.
Since it takes a few machining operations and a totally different fire control group to build a true select-fire assault rifle, I'm not really keen as to why the bolt carrier was modified, but businesses are known to attempt to exceed certain standards in government regulation to show good faith and try to avoid litigation.
As more and more AR15 owners attend high-volume formal training courses, including LE & Gov't agencies, people have realized that significant deviations in the tried and true formula for AR15 reliability lead to guns that simply fail, usually within the first 150-300 rounds of Day 1. The companies that build well-renowned AR15's have been specifying M16-weight carriers for quite some time now, to keep the operating parts in-balance with over-gas. In a 5.56 or Grendel, I wouldn't think of using any other weight carrier than M16, in addition to a heavier buffer with heavier internal weights.
Since it takes a few machining operations and a totally different fire control group to build a true select-fire assault rifle, I'm not really keen as to why the bolt carrier was modified, but businesses are known to attempt to exceed certain standards in government regulation to show good faith and try to avoid litigation.
As more and more AR15 owners attend high-volume formal training courses, including LE & Gov't agencies, people have realized that significant deviations in the tried and true formula for AR15 reliability lead to guns that simply fail, usually within the first 150-300 rounds of Day 1. The companies that build well-renowned AR15's have been specifying M16-weight carriers for quite some time now, to keep the operating parts in-balance with over-gas. In a 5.56 or Grendel, I wouldn't think of using any other weight carrier than M16, in addition to a heavier buffer with heavier internal weights.