USMCSGT0331
"I just talked to Chris Higgins about the "Mk13 Mod 3" that's up for auction at the CMP right now. He said that it's not currently a Mk13, it's not a prototype Mk13, and it's not in any sort of fielded Mk13 configuration. This rifle was built from original Mk13 parts (Mod 0/3 receiver, Mod 3 bolt, Mod 5 chassis, sorta kinda Mod 7 barrel) and was used exclusively to test silencers for the Mod 7 contract.
This is not a Mod 7 prototype, this is a purpose built rifle that used original Mk13 parts, and was only used to test silencers. There were others like it built, so it's not a unique example. Chris definitely leaned on the fact that even though the parts are Mk13, the rifle itself is not a Mk13 and the CMP should not be calling it a Mk13 Mod 3.
The barrel is cut further back from the rear of the flash hider because there were about 10 different options to test and some muzzle devices or silencers needed more room to fit on the barrel. So, the muzzle end of the barrel was profiled like this on each test rifle to keep things uniform and make it so that everything being tested could be used on each rifle.
I hope this makes sense, if anyone has any questions, please ask them here and I'll do my best to get some answers for you."
www.snipershide.com 
