I use a P14 bolt for any caliber larger than a standard belted magnum
LOTS of spare metal on the left side of the P14 bolt for these big boomers, yes the rest of the rim of the bolt is thin, but the left side is good
I have built over a dozen 505 Gibbs on Enfield 14 and 17 receivers, and have another one in the shop I am working on
It takes the proper machine and hand work, a new extractor with the thicker M70 hook, and longer overall length to stay in the rear bridge, a new proper magazine unit and follower also a good magazine spring for these big conversions
Simply not a normal type of everyday garage gunwork
WCF