In reply to:

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Mac,

While your at it, maybe you could help me out on a "project" I want to have done. I'll be getting a set of Valmet 375 Win Big Bore barrels and would like to re-chamber them to 375 FM. The problem doesn't appear to be in wall thickness or the sort. I have a set of '06 that were re-chambered to 30 Super and they work just fine.

My concern is the rim thickness... .063 in the Win and .055 in the 375. Do you have any suggestions as to what I might get into here, and what else I might consider? I was thinking of using a 348Win case, but the base is somewhat larger, and it isn't a commercialy produced round like the 375 FM??? Also, I want to drive 300 gr bullets at 375FM velocities without high pressures.

Can I build up the extrector rims a bit and cheat with the headspace a bit...is this all too spooky...?

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First off, the 375 H&H FL should clean out the old chamber, and and the rim diameter of the 375 H&H FL Mag will clean out the rim as well, so headspace will not cause a problem! The one place that needs looking at is the diameter of the 375 FL case at the point of the case mouth of the 375 Win. The numbers are:

375 FL

rim dia= .572

head dia= .511

shoulder dia= .450

lngth to shldr= .2.40

rim thickness= .05

375 Win
rim dia= .506

head dia= .418

shldr dia= .NA

lngth to mouth= 2.020 (dia at mouth .400)

rim thickness= .063

375 JDJ

rim dia= .510

head dia= .464

sldr dia= .452

lgnth to shldr= 1.809

rim thickness= .062

One needs to look closely at some precision drawings to be sure, but I think the 375 FL will clean out fine, and the extractors can be opened up as well, I think.

I know the 375 JDJ will cleanout the 375 Win chamber, because I had one done a few years ago, and it worked like a charm. Now T/C is makeing factory ammo for the JDJ! I don't know what pressures are involved with it, but it is most likely not too hot, because they are for their T/C pistols! The barrels have a 1 in 12" twist, which is standard for a 375, so the bullets you use will not be a problem.

Hope any of this helps, but if I were you, I'd touch base with someone who has some scale drawings, to avoid leaving a ring in the chamber wall, before cutting a new chamber! However, I don't think the headspace will be a problem.