Steve,
Lots of nice choices there.
The No 4 is good for 42,000CUP. Several writers on the old Enfield boards i used to frequent felt the figure is very conservative. That elusive German gunsmith chambered them in all sorts of non-mag modern calibers, stating that the action is much stronger than given credit. He had regular 7x57, 6.5x55, .444, .45-70, ass't Rimmed and some other Euro's among the selection.
Weeeel, I do have a '0' bolthead to start with. And what with me lapping in the lugs, a 'smith can bbl it pretty tight. But, I'm happy with 42,000, Only want to do this once, even if JIC I do have a '1' & '2' in the parts bin.
Were I to go with a .303-based rimmed wildcat, the .257 Roberts or 6.5 Rimmed something and a long enough bbl for good balance would work well. The .375 2 1/2 is pure classic, as a source is mentioned in a following contributor's post. E-mail sent to that 'smith.
Also checking with a correspondent in Oz, tho I understand permissions to export are hideous to obtain. A New Zealand fellow puts out a very nice practically-stocked .35/.303, and he also is unable to export a bbl or the stock set.
And, too true, i had hoped to find an already 'rolled', low-milage bbl. However, as is usual for this resource here, there are plenty of possible suggestions. I suspect the final choice will pretty much be what I find, rather than made to order. However, one never knows.
Thanks, J.
