No1Mk111 Receiver Holding Fixture

[Surpmil]

Since the bolt ways are not likely to be of identical diameter, perhaps a mandrel split into four for part of its length and bored and tapped slightly undersize for a bolt would allow the mandrel to be "spread" and grip the boltway behind the locking lugs, which is almost the only place it has much support.

Might be a good idea to have the same feature at the opposite end as well, though the contact area is minute by comparison. Mounted that way, the front body face could be made 100% square to the bolt way and the barrel threads at least checked.

Makes me wonder if they did some subtle barrel "truing" as part of the collimation process, ie: dropping said barrels onto wooden blocks etc.