I sent Bushmaster an email last night asking some questions about the new Bushmaster Carbon 9mm carbine I recently got in a trade. Thought I'd share what I learned for those that might be interested in making modifications to theirs:
1. The barrel is secured with an AR barrel nut. There is no torque specification. We turn the barrel nuts on by hand then snug it up using a Armorer's wrench by hand. Then with a 1/2" drive torque wrench or breaker bar installed on the wrench turn the nut on two more gaps in the teeth of the barrel nut for the gas tube alignment.
2. The buffer extension tube is slightly larger than the Mil Spec. A Mil Spec tube can be installed.
3. They use the standard AR type carbine handguards that we use on our AR15/M16 type firearms so the railed type handguards for carbines can be installed.
4. The barrel threads are different than the AR 1/2" X 28 tpi threads. The 9mm threads are an industry standard of 1/2" X 36 tpi so an AR type muzzle brake with smaller diameter muzzle opening can not be inadvertently installed. Brownells www.brownells.com carries a number of the 1/2" X 36 tpi compensators and muzzle brakes.
Thanks for the feedback on the other rifles.
Jim Eden, Tech Support
Does anyoen know how resistant carbon fiber is to heat? I'm considering spraying my upper and lower with Norrell's moly resin but I'm not sure what temps it can withstand when I bake it. I don't care for the mottled look of the upper and lower as they come from the factory.