While cleaning my 12.5 *** barrel Franken gun I noticed some leaning on the rear of the barrel extension lugs. It mildly concerned me because it means something is a little out of time or spec.
The cam pin slot, cam pin, and BCG to upper fit control the alignment of the bolt and barrel extension lugs while the BCG is going forward feeding a round. As the BCG goes forward and strip a round from the mag the round is trying to push the bolt back. Because of the tolerances involved sometimes it can cause the bolt to over rotate slightly and misalign with the barrel extension lugs. In turn the bolt logs with slam into the back of the barrel extension lugs and will result in these little peened or raised areas.
An AR15 isn't supposed to do this, but can get away with doing it a little. As long as it isn't sever or impeding forward movement of the bolt as felt while hand feeding it or during operation. Personally my pictures below are about the limit I would want. Thus gun has had 500+ rounds through it with a suppressor and adjustable gas block on it while hunting. I hope my discovery and slight research will help someone else.
The cam pin slot, cam pin, and BCG to upper fit control the alignment of the bolt and barrel extension lugs while the BCG is going forward feeding a round. As the BCG goes forward and strip a round from the mag the round is trying to push the bolt back. Because of the tolerances involved sometimes it can cause the bolt to over rotate slightly and misalign with the barrel extension lugs. In turn the bolt logs with slam into the back of the barrel extension lugs and will result in these little peened or raised areas.
An AR15 isn't supposed to do this, but can get away with doing it a little. As long as it isn't sever or impeding forward movement of the bolt as felt while hand feeding it or during operation. Personally my pictures below are about the limit I would want. Thus gun has had 500+ rounds through it with a suppressor and adjustable gas block on it while hunting. I hope my discovery and slight research will help someone else.
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