Posting for reference, if anyone has questions about Turknelli etc Bolt Carrier Link (the pivoting bar at rear of bolt which engages the recoil/return spring):
One the right is the stock link from my Turknelli2/Revolution R4, it's well built from common thickness sheet steel. Some wear is observed on the corners of the rear point, this seems typical as they break in (800 rounds on that one).
I was able to deburr that with a good file, and would say the hardness is moderate, but not too hard, and the alloy is good quality.
The bolt link on the left is one I pulled from another bolt assembly, likely also turkish mfg, but of slightly better quality overall: the cut quality and fitting is very good (laser cut, instead of punched). I took a file to the rear point corners as well, it was a bit harder than first example, but not too hard (still cut fine with a good swiss file).
These sheet-metal built links are a good and reliable design, I've heard the Canuck m4 uses a one-piece link, which is nice, but likely not to improve reliability in any way. Benelli originated the design with a sheet-metal built link.
Interestingly enough, the bolt carrier itself in the R4 was the better of the two I've got on hand, in terms of smooth action quality. It's certainly beneficial to have more than one of each part, if you're interested in gunsmithing with these shotguns. I'll have another R4 here this week to pick apart and see what more I can learn.
