If you measure the water volume/weight in grains of the .375/338 vs. the .375 H&H to the nearest grain, filling the cases as closely as practical to a flat meniscus at top of neck/case mouth:

.375/.338 (RP case) >> 91 grains
.375/.338 (W-W Super) >> 94 grains

.375 H&H (RP case) >> 94 grains
.375 H&H )W-W Super) >> 97 grains.

Pretty close, and maybe the .375/.338 is more efficient than the hallowed .375 H&H.

Well, if I want to settle for a long action, I guess I can just use the reduced loads I've developed for my 375 RUM.

However, these things are a matter of taste and sometines just stubborness...I love the 338 winnie and the idea of just bumping it up to 375 in a 22 inch sporter has me hooked.

I'm kinda chimin' in late on this one, but I do have some comments and thoughts. Yes, I am a proud owner of one of these beasties.

How did it happen? Well I had a Win 70 in 300 Win that wanted to make bigger. I was an experienced reloader, so wildcats didn't scare me, plus I NEVER used factory stuff except for .22's.

I was originally gonna go for a 358 Norma. My smith had a 375 H&H take-off barrel. One of those "the guy decided a 375 H&H was too much for him" deals. Cut a little off the barrel shank, rethread and rechamber and Voila! This would be the economy route to getting a 375-338.

I'd have to say this at the threshold of my shooting comfort. 300 grains at 2,500 is not much fun after 10 rounds. I can do a box of 300 Win's or .338's fairly easy.

I checked the expansion ratio thing, and yes, the 375-338 is right there with the .308. That's why IMR 4064, RL 15 and Varget have worked so well for me. Sabot, you should forget about 4350 - it's just too slow. I tried it with the 270 grainers and with a full case could only get 2,400 fps.

The advantage of the .375 bore over the .35 bore is that the heavy weight bullets are more heavily constructed.

I have found that 66.0 grains of IMR 4064, RL 15 or Varget
give me 2,500 fps with a 300 gr Nosler in a 21" barrel.
This is my standard load.

Why do I have one? Mine is a close-range brush hunting rifle for S.E. Alaska. Peep sighted. Give a guy real peace of mind when in coastal brownie country. Sure, it's overkill for our Blacktails, but certainly less meat damage than a 300 Win.

My friend Paul (now deceased),and I shot my 375-338, and
His 700 BDL Rem 375 HH side by side thru the same
chrono. The 375 HH was loaded to max loads from the
Barnes manual, with 210,235,250,270, and 300 gr.
Barnes X bullets (molycoated). The same bullets in
the 375-338 came out the same velocity with 5 Gr.
Less of RL 15. Mine is now on a 1909 Mauser with
a Boyd Laminated stock with crossbolt behind the
recoil lug and glass beded. Timney trigger and Muzzle
Brake. It is real pleasent to shoot. My wife who has
shot a full house 340 Wby with a brake says it is
a pussycat.
Lyle

Muskegman, (and all others)...

I've been shooting the big brother to the 375/338 (375 Taylor), the 416 Taylor for several years. I've tried all the powders mentioned above, except Varget. At first RL-15 was my powder of choice, but then on a whim I tried some H4895 and my rifle loved it! Sure, it's an older name in the powder world. Maybe not as old as IMR 4064 though. But, Hodgdon has upgraded it as part of their 'Extreme' line of powders, and it's fairly short as far as kernel length goes, so it 'throws' well in a powder measure. Plus it's suppose to be 'temperature IN-sensitive.' It also gave slightly higher velocities than the Reloader powders.

Hey, can we call it the 9.5X64? That should help overcome the bias against the 375 bore

I have a real honest to goodness 9.5X64 Improved on a Ruger 77. It features a 375 bullet in a 9.3X64 case which has minimum taper and a 40 degree shoulder. It is a very efficient round and easily duplicates 375 H&H FACTORY rounds. When I had it made RWS 9.3X64 brass was plentiful from Huntingtons, but now it is a bit harder to come by. I would imagine the 376 Steyr would get close to what I get with my 9.5X64 Imp, but probably not quite as much. I have been tempted to order some 376 cases to see if they could be reformed to my 9.5X64 Imp easily. Or, I may just have to put together a 376.

I've built three wildcats in my lifetime and my reasoning has always been that a wildcat must offer something I can't get in a standard factory load.

My 20-.233 was a caliber unachievable...it qualified!

My .243 superrockchucker really didn't quality. I'd not build one again. The 6mm Remington is nearly as good.

My 6 X 45 qualified in weight of rifle. At the time in Minnesota, a legal deer rifle had to be larger than .22 caliber and the 6 X 45 allowed me to be legal and still have a very light rifle. It really works too!!!

For those of us that want to convert over .300 mag M-70 CRF actions the .375-.338 seems to be the bees knees. But what's wrong with the .375 Dakota? No belt....more powerful than the .375 H&H......'06 length action.....standard cartridge!

Granted, I haven't seen any .375 Dakota ammo sitting on dealers shelves....or brass either for that matter...but I assume it's available...?

I have to agree with Paul H on this one !!

The RUM is interesting and that would be my second choice to the H&H in the .375 Bore.

I can see the benifits of the .416 Taylor but just can not quite grasp the .375 Taylor due to the availbility of the wonderful .375 H&H with headstamped brass etc. I have a little thing for headstamped brass for some reason