LongBranch made replacement barrels for the #4 as part of the DCRA target rifle program. members could send their rifles in to be checked over and re-barreled.
The barrels came off the machines complete with bayonet lugs that were usually, but not always, ground off.
A DCRA barrel can be identified by a 4 digit serial number and a stamp that looks a bit like a maple leaf.
LongBranch may have made 7.62 barrels for other purposes, but the DCRA barrels are the most common version seen.