Home Forums Reloading Big Game Rifles .375 h&h AI

I’m new to reloading and have a few questions on what I’m seeing in these pics....

I went to the range today to test these new loads but stopped after the first 3 shots as I didn’t want to kill myself.

I’m shooting a Sako AV in .375 H&H Ackley Improved.
Cases are Federal nickel plated fire formed in this chamber from factory loads.
Bullets are Barnes TSX 300g
Primers are Winchester Large Rifle Magnum
Powder is W760
Coal=3.637

Starting load was 79g, working up to 84g in 1g increments.
Average FPS for 3 shots at 79g was 2580fps (2579,2594,2580).

I stopped after these 3 shots as I was getting marks on the base of the case from the bolt?, and sooty material on the outside of the case neck. Bolt lift was firmer than when closing the bolt, but not tough or difficult.

Are these signs of excessive pressure? What do they mean? Am I in the ballpark of proper loads here or should I reduce loads or switch to another powder? I know that load data for this cartridge is scarce and most people say to look at 375 Weatherby or max 375H&H loads for starting loads. Thanks!!

I am no expert, but from what I have read is if you have soot on the case neck there isn't enough pressure to properly expand the neck allowing powder residue to blow back down the case in the chamber. Hopefully someone will come along soon that can confirm pr refute this.

By the way, that doesn't look like an excessive amount of soot to me.

Your velocities indicate that the load is pretty tame. Some dataI found on the .375 Weatherby shows 300’s @ around 2750 to 2800 FPS. But, that’s just part of the story. I’ve never run 300 TSX’s thru mine, so I can’t give you any real input on expectations. However, I’m getting 3130 FPS with 250 TTSX’s......though am seeing some pressure indications. But, getting good brass life!

In looking at your photos, I don’t see anything to be concerned with. But, merely looking at the photos may be misleading! Your primers aren’t “flattened. The primer doesn’t appear to have any cratering. The soot in the neck region is not that uncommon. If you had heavy bolt lift, I’d start being more concerned.


How far are you off of the lands? Barnes Bullets like to be pretty far off of the lands....Barnes suggests starting @ .050” off of the lands. If you are up against or very close, it may give increased pressures! Hopefully, someone with 300 TSX info can chime in! memtb

I tend to agree with Just a Hunter, about the soot. I would lean toward the neck not sealing against the chamber walls, because of low pressure! memtb

Looks like case capacity is similar to 375 Weatherby which there is data for. Google 375 H&H Improved loads and 375 Weatherby loads.

Look at Nosler load data for 375 H&H 300 gr WW 760 velocity to get a ball park.

Case neck soot looks normal to me are primers protruding?

Prefered other powders than WW 760 when I reloaded for 2 375 H&H and Fed cases can be soft and show pressure early.

While a lot of people bad mouth RL 17, that’s what I’m running in my AI. Getting good velocities and great accuracy! I pushed my 250 TTSX’s up to 3160, but the groups started to open up, so came back to 3130 which worked well! memtb

I’m not sure how far off the lands I am. I based my CoaL by the crimping groove and maxing out magazine length. I shot 3 rounds of older Factory federal 300g partition to sight in my scope. There were no marks on the base of the round and very little spot marks. Although the factory stated FPS on those rounds is 2570, I was only getting 2250.

smthgfshy, I’ve never chrono’d a factory round through my AI, but, I’m surprised that you appear to be losing that much velocity! I would have expected much less loss! memtb

I own a 375 H&H AI.
The advice above is good. I’ll add one thing ww760 seems sensitive to temperature variations. The 4350 powders are in the same general burn rate. I’d be looking at those powders.
I’ve had issues with the older ww powders going high pressure in high temperatures. I no longer use them. I understand that Winchester has come out with better powders, I just have not used them yet.

I’m in Alaska. Temps at the range today were in the 60’s.

I believe that temperature in Alaska varies as much as it does in SD. Though maybe not.

An example of what I’m talking about. I had been shooting a “decent” load in my 300 Win Mag Using ww785. One Sunday afternoon I went to the range near Ft. Peck MT. The temperature outside was very warm and it was getting hotter. I fired one round and walked 100 yards to the target and back (I needed the exercise) there was no pressure sign on that cartridge, the primer rounded. I shot a second round, walked down to the target and back. The primer was a little flattened. And so it went. Each time I let the rifle set idle between rounds. Each time the cartridge looked like the pressure had increased. The fifth round the case was stuck firmly in the bolt face. I had to take it home to my shop to get the case free.
I had problems before with ww748, ww760, ww760-BR, and now ww785. The only use I have for older ww powder after that incident with ww785 was with light loads which I used for fire forming and I was sure not to use any at high temperature.

In your incident the load was likely a low pressure load.

What I meant to say and evidently didn’t do a good job of saying it,
I have found The old ww powders To be temperature sensitive. The sensitivity goes both ways. If the load is developed at one temperature and used at a different temperature the pressure could increase or decrease and it’s been my experience that with these ww powders the pressure change is greater than I feel is acceptable.

Therefore, I recommend that unless you are in a climate where the temperature changes little avoid the older ww powders.

keep in mind that the 375 weatherby chamber has some freebore , while your AI chamber may or may not............so if you use weatherby data , approach with caution

with the larger than H&H chamber , you can go to a somewhat slower powder than 760 or 4350 if you wish

I burned alot of IMR 4831 in my weatherby , and my favorite load ended up using Ramshot Hunter

From wikipedia

"The case capacity of the .375 Ruger is 99 gr. of water (6.42 cm3) .
The 375 H&H Magnum has a case capacity of 95 gr. of water (6.16 cm3), an increase of 4% for the Ruger
Case Capacity of the 375 Weatherby Case is 105 gr. of water (6.82 cm3) an increase of about 11% over the H&H and 5% over the Ruger. (the FreeBore/Leade for the Weatherby is 0.373 thou. as per the Factory Spec's"

I believe the case capacity of the 40 degree 375 H&H AI is marginally greater (in my rifle) than the 375 Weatherby, by how much I don't know, (300 Weatherby ammo chambers in my AI (I have not fired any Weatherby in my rifle, but have H&H. And I don't have any 375 Weatherby ammo.)

I've not found a lot of data on the 375 H&H AI, I have various bullets 220 grain to 300 grain Jacketed and a few cast bullet molds. I am concerned with using Weatherby 375 load data due to Free Bore in the Weatherby.

I'm thinking 3,000 fps with 235 grain to be about top, maybe 2,800 fps with 270 grain, and 2,700 fps with 300 grain. The lighter bullets and the cast bullets will be for practice off-hand shooting.

I plan on working with this rifle this Winter if the weather cooperates.

I know someone may worry that this is an old thread and will have to mention it. Other than that any thoughts other than bashing, thanks.

Tilt the powder jug more!