Originally Posted by
Dano5326
Almost 20 years ago I had some 12.5", perhaps the first USG ones, uppers made for M4's. The reason was simply as short as possible while able to mount the m203 (9" barrel) using the barrel knotch mount of that era. A side benefit was the increased length made for a better size stick to pumel non-compliants with.
We did not change the gas port size and had no issues.
OAL w/ suppressor is handier vs 14.5"
Also the MV is greatly improved over the 10.3"
There is certainly a potential reliability increase, considering the dwell time, with a wider range of ammunition and tempature ranges.
In short a happy medium