Anyone know the trim to length for the .375 Ackley Improved? Thanks.

MIke

Are you rechambering a standard 375 or starting from scratch? If rechambering, doubt if length makes a difference as the AI brass will always come out shorter after fireforming than the parent case.

I have one. It is new to me and I have only shot it to date with .375 H&H ammo. I have some .375 AI dies and wanted to load some.

The fired ammo will always give a case shorter than the original H&H chamber or parent case. Just trim them enough to even them out, if you even care about that. The chamber isn't going to care.

Thanks for the feedback Mike. I experimented trimming to 2.820 and 2.815 and both chamber fine. I will load up some 300 grain TSX and let 'em fly.

My 98 is 2.820".

Rich

It seems there were a few variations on the max length of the .375 H&H Ackley Improved, from 2.814" to 2.830".

Lately, since the 1970's, it seems to have settled onto max 2.830" brass length,
as per a Clymer reamer that had a 40-degree shoulder angle and called itself simply ".375 H&H Improved."
So, yes, that trim-to-length of 2.820" would be a good recommendation.

The .375 Weatherby Magnum of 1945 & 2001 (CIP/SAAMI re-spec-ed in 2001 with perfected throat),
has a max brass length of 2.860", trim to 2.850".
Norma factory brass matches those specs.

+1 on NFMikes post.

I have a rebarreled Pre 64 Mod 70 and if I need to trim at all I use 2.85" and try to get all cases the same length. For DG and Airline travel, I also crimp slightly with a Lee Factory Crimp die. Local practice this step not necessary.

Good Shooting

Tetonka
DRSS

+2 on NFMike's posts.

I have a Jarrett Rifles 375 Ackley Improved on a Rem 700 action. Same goes here, the 375 H&H cartridge shrinks after fire forming to 2.820+/- and I ended up using 2.810 as the trim to length. Super tight at 100 yards with Hornady 270s and almost as tight with Barnes TSX 300s with both bullets grouping under an inch. Barnes used exclusively on seven animals including a cape buffalo last summer. Excellent choice.

I did have a problem crimping with Redding dies due to the shorter case length. I ended up sending my original 375 AI dies back and they sent me a new set with a "shorter case" crimp capability, otherwise it would have been a Lee factory crimp die.

Tom

I trimmed to 2.820, then loaded with 300 grain TSXs (F215M and RL15). My Cloward shoots a three shot group just over .5" at 100 yards. That seems to be a good enough recipe for me. Velocity is a little light at just over 2400 fps, but not sure anything it hits would really notice.

Mike,

The 375 AI and the 375 Weatherby are nearly the same round for all practical purposes and H-4350 gives over 2700 fps with no pressure and excellent accuracy in my custom 375 Weatherby. Like you I started with R15 and got good accuracy but slow speeds. Guys here pointed me to H4350 and it seems to be the powder.

Mark

Yes,
Start with 80 grains of H4350 Extreme and any 300-grain bullet you want ... work up ... and never look back.

Must be too old to appreciate hot rods any more. To me, a 300 grain bullet going 2400-2450 fps is perfectly fine. Why pay the price in recoil and muzzle blast to push that up 200 fps? Will it make any difference on the receiving end? And who needs a .375 that shoots flat enough for 300 yard shots -- I want to be close particularly if it is something that fights back.

So the obvious question is, why in the hell did you buy a .375 AI then dumbass? Because it was a Cloward built on a Remington Model 30 action and I am sucker for pretty rifles.

To be absolutely sure of the chamber and neck length, have a chamber caste made...THEN you know for certain how long of a neck you can play with...or at least measure the chambering reamer or obtain a line drawing of that reamer.

It is true that z standard cartridge always shortens when fired in an AI chamber, but the amount depends on what case you begin with and what size that case is in relation to the final AI size.

If you start with a 416 RM case the amount of stretching is much less in all directions and the final OAL will be less than if you use 357 H&H brass. And you might end up with a full length case due to the larger 416 neck lengthening when run through the 375 AI sizer die. You can also use 375 Weatherby brass, it is just a bit larger in the shoulder that the AI chamber.

Whenever I do a wildcat I try to start with a larger case and do a size DOWN instead of a size UP because of these different factors.

But in all reality you are only talking about 0.005" to 0.020" which doesn't amount to a hill of ant schat in the long run.

My 375 AI specs list 2.83" OAL and I would guess the chamber is cut that length at least, so 0.010" below that will work OK.

Nothing wrong with the 375 AI, it is equal to a 375 Dakota or 375 Weatherby and not much behind a 375 RUM in case capacity OR actual killing power.

In todays age I wouldn't rechamber a 375 H&H to the AI as there is the 375 Rum available with quite a bit more thump and very little additional work to the action and you can still download if you want.

I agree a 300 gr bullet at 24-2500 fs will handle most chores and if you need more slap, go to a larger caliber with a heavier bullet at higher velo.

Luck