Re: 1917 Enfield for 338 Lapua?
Wayne, 9 lug MKV Wby's are good donor actions for boomers. Calibers of .300 Wby and up can take approx 3.8" OAL loads as is. If the bolt face needs opening, they are easy to do, and extractors, mag boxes, followers etc, are available from Wby. Excellent aftermarket stocks are also available.
My experience with the 300gr Smkhp's is that they can be seated short enough to go in the mag box, but they eat up powder capacity. I shoot .338 x .378 at 4.00" OAL and single load each round.
I don't know how long the P-14 or P-17 can go. You may be able to pick up a Mk V for less than the cost to rework the Enfield. Just be sure it's a .270 Wby Mag or larger. The .270 and the 7mm Wby Mags need the bolt stop slot lengthened to work. Also easy to do.
If you find a Mk V donor, count the lugs, and check the magazine OAL before you buy it. The .270 and 7mm will have a partition snapped in or welded in the back of the mag box. Also, some standard length Belted Magnum Mk V rifles are available, and will have a partitioned mag box and 9 lugs.
Good luck. Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time