Do you gain enough with the Ackley Improved 375 to make the conversion worthwile? I knop you can use 375 H&H ammo in a pinch but how much velosity do you gain with 300 gr bullets?

Hawkeye,
You would gain a about 100-150fps over the H&H with the 300 grainers.
The AI, Weatherby, JRS, etc. seem to be much easier to load for. Powder compression is not as severe with heavy bullets and max loads. Case life also goes up sustantialy because head space is not as difficult to establish. Recoil is still mild.The 375 Weatherby is great choice if the reamer is available. It is also very accurate despite what some would say.
The 375 Ultra gives you a little over 300fps over the H&H, but is a more difficult project and recoil is a little stiff for an unseasoned shooter. The Ultra and the A.I. give you the option to load down if Africa is in your future.

Jamie

X Man,

Thanks for the post. I definately plan on going back to Africa for Buffalo but will use a 416 or 458 probably. I'm wanting to build a light weight 375 on a Stainless Classic Model 70 action and chamber it for 375 something. The reason I am looking at the AI version is I like the case better than the 375 Weatherby. I never liked the rounded shoulder on them. I fear the recoil on the 375 RUM would be too much in the light rifle.

I have a 375 improved and love it. No pressures. 2800 fps, 300 grain bullet, 21 inch barrel, and 1 inch 5 shot groups.