My brother recently purchased a Mk3 CBR. He received it yesterday (Friday) and we took it out this morning to go shoot. It shot fine, the Geissele trigger was fantastic and the Surefire SOCOM brake was great as well. However, after a total of about 50 rounds, a few problems arose.
First, the Surefire brake became loose enough to remove with my hands. The provided shims (in any combination) did not properly index the brake when we tried to reinstall it, which leaves me to believe the brake was just loctited on the threads, which burnt off as the barrel got hot, without properly indexing the brake using the correct shims. That's not too huge of a problem, a few more shims and some Rocksett will solve that. The second problem is more serious.
Secondly, he bought a CMMG rail section to attach a Harris bipod adaptor/bipod to. Instructions were followed to the T for mounting. After shooting a few rounds (only 20 or so) in the prone position, he noticed the bipod was loose. When he inspected it, he saw that the keymod rail attachment actually sheared through the keymod rail. He moved it forward a few slots, and after a few more shots the same thing happened. Either the holes were drilled too big or the aluminum was too weak to support that kind of stress (which is ridiculous for a .308 rifle with a SS barrel to not be able to be shot from prone).
He has sent an email to CMMG concerning this, but since it is the weekend I assume they won't get back to him until Monday. Has anyone else had problems like this?
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