Since there isn't much published data on this bullet I emailed Woodleigh. Here is their response:
For both SN and PP 350gr bullets in 375 H&H use
Federal 215 primer
68-72 grains Hodgdon H4350 for 2300-2380 fps
or
73 grains H4831SC or IMR 4831 for 2250 fps.

For FMJ reduce the SN load by 5% and work up.

These are the only loads we have at the moment.
Regards,
Geoff McDonald.
WOODLEIGH BULLETS
PO Box 15, Murrabit, VIC, 3579, Australia
Ph. 61 3 5457 2226
Fax. 61 3 5457 2339
zedfield@iinet.net.au
www.woodleighbullets.com.au

This along with the data previously posted by others on AR should give a good start.

We use 74grns of AR2209 (IMR4350) with Woodleigh 350grn 375 solids at 2420fps MV.
73grns of 2209 for 2360fps mv.

ozhunter

What twist rate is sufficient to stabilize the 350 grainers?

quote:

What twist rate is sufficient to stabilize the 350 grainers?

Don't hold me to this but here is what Doktari said during his buff hunting seminar in Dallas: Most 375's are made with a 1 in 12 twist. The twist rate for the SD of a 300gr 375 should be 1 in 15. The too fast twist rate (1 in 12) sometimes results in poor penetration at close ranges which he has observed in finishing shots because the bullet has not had time to stabilize (it is over rotated). A higher SD bullet like the 350gr 375 needs a faster rate of twist (1 in 12?). So the twist rate on your standard 375 should be better for the heavier bullet. BTW Doktari said he as contacted H&H and they do not know why they settled on the faster twist rate when they developed the cartridge. My theory FWIW is that the engineers designed the rifles for 350gr bullets in the first place but they couldn't get adequate velocity with the powders available in 1912.