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.

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[tbonesmith]

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.)

Or maybe at the rear the mandrel could be made 20 thou undersized to allow a brass or steel bushing made to fit the individual rifle to be sleeved over? Hmmm...

[Surpmil]

Or maybe at the rear the mandrel could be made 20 thou undersized to allow a brass or steel bushing made to fit the individual rifle to be sleeved over? Hmmm...

Could be, although it would not give any positive "lock" between the mandrel and the body, unless some form of adhesive or soft solder were used. I wondered if a mandrel split into two halves might be better, but thinking about it in cross-section the four way split would be more likely to grip evenly and align accurately if the slits were aligned with one vertical in the bolt way.

A driving lug made to bear against the side of the "cocking piece recess" in the butt socket could be threaded or soldered onto the mandrel; or welded/brazed/silver soldered if the mandrel was finish machined/ground afterwards(?)

Thinking a little more, a long taper on the lug which would just fit the recess might be better: insert the mandrel until the lug bears on both sides of the recess. That way one could rotate both directions if a dividing head was in use.

Actually, there would be a tendency for the mandrel to work itself out with a tapered lug, even with a long taper....maybe ditch the taper idea and just make it parallel sided, but undersize 10 or 20 thou and shim it in with brass shim stock on either side. Make it 40+ thou shallower than the recess so there would be no chance of the mandrel being pushed upwards by the lug & shim hitting the bottom of the recess?

And going back a couple of steps, the mandrel would need to be counterbored down to the point where the expansion was wanted so that the threads and therefore expansion would not occur before that point. Totally obvious that I guess.