Hello, This is my 1st post here. It is not news that reloading supplies are limited to say the least. I have a somewhat simple question but have not found any direct answers on the links here, ( or anyewhere else) please redirect me if I am wrong. I am an experienced reloader (35+ years but trying to get the science of it down), but with mainly pistol and smaller rifles that are more recent & popular loads that there is a ton of published data for. I am most likely over thinking this, but here it goes. 1. I have a great Pre-64 Model 70 in .375 Weatherby Magnum I inherited from my Dad. I really want to use it on a hunt this year. It is a field grade hunting rifle, but Factory Ammo is out of the question - 6 bucks a round and only in 300gr - OUCH on the Shoulder and Wallet - really bad! 2. I have multiple manual (including recent One Book / One Caliber). Have been web searching but all sources only give data for Hodgdon Powders. 3. After much waiting in lines (mostly left stores empty handed) I was able to get 1 lb. each of some IMR 4350 and IMR 4831. I am trying to work up loads with Hornady Interlock SP 225 gr. (4350) and Hornady Interlock SPRN 270 gr. (4831) 4. Unless I find some 215 primers I am stuck using Remington 9 1/2 Large Rifle Primers. I just fire-formed & Weighed New 375 H&H Hornady Brass as well. 4. Does anyone have a formula or something I can use to set myself up with starting loads for a conversion? With the pretty heavy recoil and lack of reliable supplies I cannot afford to test shoot dozens of work up loads from way too weak to acceptable. Plus do not want to break myself or the Rifle - safety 1st. 5. I have checked other Magnum Rifles for comparison, my Manuals show about a 9-10% reduction for IMR 4831 in a 378 Weatherby with a 270gr. And about a 2-3% Reduction for IMR 4350 vs H4350. Thus my plan is to use the same % in my 375 Weatherby Hodgdon Data. 6. I am thinking right? I am not looking for MAX loads, but accurate Hunting Loads to 400-500 yards. I have found more than one thread about the pros and cons of both powders, and about Magnum vs STD Large Rifle primers, but not comparisons of load amounts. Since I can not find any other powder I can not use the testing I have always used in my other guns. Plus at 90ish grains per load I get only about 75 reloads out of a pound. Thanks for all the great reading on other posts and hope we all get tags this year and have ammo to use them!