I bought a new Winchester 375 a few months ago, and am going to start load development. I'll be trying a few 300gr bullets, but am looking for powder suggestions. So far after looking at some manuals and Ammoguide, RL15 seems like a good place to start. I have quite a lot of IMR4831 and 7828ssc, but the conventional wisdom seems to be to use a faster powder in the 375 H&H. What has worked well for others?
Also, are guys using regular or magnum primers? I'm not sure magnums are the best choice with faster powder, but doubt it would cause problems.
I know I hove been hanging out here too long, as I now consider this to be my "medium" bore rifle.

RL15 has delivered the best results in my CZ with 270 grain TSX bullets. With 300 gr TSX, Win 748 was slightly better. I'd suggest starting with RL15 because so many people have had such good results with it. If it doesn't work for you, certainly try something else. But it's a great place to start.


LWD

Mine worked well with W760 with 300gr bullets. RL15 seemed to do better with the 250gr-270gr. bullets.

Marty,

RL-15 is a great 375H&H powder but there are many and like you've already summized IMR-4831 is a tad slow although it has given me great accuracy but so-so velocity.

IMR-4064, H or IMR-4350 & WW760 are popular 375H&H choices as well.

I also prefer 300 gr. bullets, too.

Good Luck with your load testing and be sure to let us know what kinda progress you're making.

I've had great success with RL-15 in my .375 H&H using bullets from 235-260 grains. Haven't loaded anything heavier. My best groups are with R-P brass, Federal 215 primers, 71.0 grains RL-15, and a Sierra 250 grain GameKing bullet seated .010" shorter than max COAL. I have shot a .347" group (almost a perfect cloverleaf) from the bench at 100 yards with this combination. All groups with this load are < 1 MOA. Don't know the velocity, as I don't have a chronograph.

On the other hand, I have a buddy who swears by IMR 4064 for his .375 H&H. I've never tried it, as I've had such good results with RL-15.

Hope this helps.

Bill.

quote:

Originally posted by Gerry:
Marty,

RL-15 is a great ..............

IMR-4064, H or IMR-4350 & WW760 are popular 375H&H choices as well.

I also prefer 300 gr. bullets, too.

I agree with Gerry

I started off with IMR 4350 with my H&H because I was already using it in my 338 win mag. I have had great success with that powder and have not tried anything else yet. I normally shoot 300 gr partitions, but ran out a year or so back and couldn't find any anywhere. I started loading 270 gr Hornady interlocks with the same powder, and they shoot great as well.

I now have a supply of 300 partitions again, as they are my preferred bullet in my rifle.

I'm using magnum primers in mine, have from the beginning.

I did just load up a test batch of W-760 to try with the 300's, no real reason but mostly out of curiosity. Must curb that bad habit before it spreads.

I hear too many good success stories with RL-15 or W-760 to not believe them. Any of these 3 powders would be excellent for you in my opinion.

Mine is also a Win mdl 70, but it is well used, not new.

Good luck.

Another vote here for RL-15. I've had great success with it with both 270 & 300 gr. bullets.

For my M70 in .375HH that I got about a year ago this is what I found worked best:

I've used RL15 at 71.5gr and a COAL of 3.57" per the Barnes manual and got sub MOA 3 shot groups with 300gr TSX's. This load consistently shoots this well.

But, the more accurate load is 78gr of IMR4350 with 300gr Swift A-Frames. This load consistently shoots one ragged hole. NOTE, this is 1.5gr ABOVE max load per the Swift manual. However even in hot weather I've not seen any signs of high pressure.

Both loads crimped using Lee Factory Crimp Die. I don't remember what the COAL is for the A-Frame load, I crimp it into the cannelure towards the front of the groove.

I've successfully used H-414 (same spec powder as WW-760), and have also succesfully used IMR-4350. The short cut versions of 4350 might be the best choices for consistent performance and optimal velocities.