Are match bolt carriers just another expensive trinket or something that really improves accuracy?
by Joe Carlos
When I became the armorer for the Army Reserve Marksmanship Program Service Rifle Team I followed the advice taught in various military leadership schools. I assessed what we had, machine rest testing all the uppers I inherited. Average group size was over a minute of angle and only 39 out of 135 rifles would shoot one MOA or better. As in Shelley’s poem, I despaired! I expected much better.
In connection with this initial assessment I recorded all group sizes and throat gauge readings. While most of the barrels were not shot out, the uppers just weren’t shooting well. From having been in the firearms business for decades I knew it could take up to a year or longer to get enough replacement barrels. Seeking a quicker and cheaper fix, I eventually cut average group sizes in half but it involved a lot of work coupled with a fair amount of trial and error. Match bolt carriers contributed their share of the improvement.
Visual inspection of the Army Reserve uppers revealed glaring errors. Lots of gas tube and float tube contact, front sight housings contacting the front of the float tube hand guards, broken float tubes, among other things. With the exception of the latter, most of those faults could be corrected cheaply with hard work and long hours. I began by tearing most of the below average uppers down to their component parts and carefully reassembling them. See my two part article in the March and April 2013 issues, “The Relationship Of Barrel Extension Diameter To Accuracy In The AR-15” for details on how to stabilize the barrel extension in the upper receiver. This alone resulted in an 18.6% average reduction in group size. Now that I am using the great BAT Machines (batmachine.com) oversized match barrel extensions I am realizing closer to a 35% reduction in group size.
Read more in our May 2014 issue. Back issues are available.