Have now had a chance to build a dummy load and section a Speer 235g bullet.
Perhaps I'll get a chance tomorrow to show the sectioned bullet, along with a sectioned Sierra 200g. The interesting thing to me is the jacket on the Speer is actually thinner than that of the Sierra - at least in the front half of the Speer. An imprecise and informal test did not show any difference in the lead hardness between the two. This leads me to believe the Speer bullet will work in the .375 Win as far as upset and expansion is concerned. Time will tell.
There is a problem with loading the 235g Speer, however. That problem is related to the length of the ogive. With the bullet seated to max COL in brass trimmed to minimum length, the case mouth is on the ogive and the bullet is easily pushed back into the case itself. This, of course, would be bad if it happened under recoil and such a cartridge was then fired. Bad kaboom. I though perhaps a Lee crimp tool might fix the problem but after some study I don't think this would be an acceptable solution. A better solution would be to cut back the case by some amount. I'm guessing about .100" would be a good minimum and .125" might be better. This should not affect load data as the cartridge has to be loaded to 2.560" max COL and trimming the case does not change this.
If it expands at 1400fps, which is yet to be determined, the 235g Speer might be a better choice than either the 200g Sierra, the 220g Hornady or the 220g Les Volmer bullets. Comparing the loads below shows the slower, heavier Speer bullet would have higher retained velocity and energy at 300 yards: The first two loads use AA1680, WW brass and Rem 9-1/2 primers and were chrono'd using my Marlin 375 while the Speer load is from Speer #14 using Reloder 7. Drops are based a a 6" MPBR zero (max 3" rise or drop). Drifts are for a 10mph crosswind.
200g Sierra, 2396fps, 185 yd zero, 215 yd MPBR @ 300 yards = -18.8", 1347fps, 806fpe22.8" drift
220g Hornady, 2230fps, 175 yd zero, 205 yd MPBR @ 300 yards = -22.0", 1321fps, 853fpe, 22.0" drift
235g Speer, 2097fps, 172 yd zero, 202 yd MPBR @ 300 yards = -21.5", 1432fps, 1070fpe, 16.1" drift
Unfortunately, I won't be able to test any .375 Win loads for at least a couple weeks.
Speer does caution that if used in a rifle with a tube magazine, only one should be loaded in the magazine. There are probably multiple reasons for this. One might be Speer does not think the nose of the 235g bullet is sufficiently round (or flat, whatever) to prevent mag tube detonations. Another is probably the problem I mentioned above re the crimp on the ogive not being sufficient to prevent bullet setback. Compressed (e.g. max Reloder 7) loads would help with this issue. I think a Lee crimp on shortened brass would take care of this particular issue as well.
