I don't blame you for wanting to know. the way I figure it you'll get about 1.3 #'s out of 100 cases. One other thing to be careful is...are the ammo all the same lot #? Could be possible that they might not be loaded identical. I have an idea to offer you if you like. Chrono a couple of shells and then when pulling the remainder down you can average how many grains per shell. I can run the idea past quick load and probably give you a pretty good estimate of what powder it "mirrors". Bottom line is even if you knew what powder it was different lots of the same powder can be off 4-5%. I would surely think it couldn't be faster than re22 and most likely a powder more like re25 or H1000.
I wouldn't dump it myself but the choice is yours. As a measure of consistancy you could check one shell from ea box and see ifthey are loaded with the same amount. (This would work in lieu of finding lot numbers.)
I think with a little knowlege to start quick load would give us a very close answer.
as far as i know, the powder used by weatherby is not available on the market. it is a mixture of powders. i can understand using the powder you will salvage, but there is one powder you may want to try. I load for a .300 weatherby and will try this powder when i get my rifle back from the gunsmith. Hornady released the superperformance powder which they claim will give "better than weatherby" performance. like the weatherby ammo, superperformance is a mixture of powders.
I would shoot them and have perfectly fire formed brass. Yes out of an overbore cartridge it's a lot on a gun but for most hunting the b tip will be a solid performer. I have used them in africa on everything plains game and the cats. They preform great and it seems like the simplest and least expensive solution, so unless u r shooting bear or perhaps moose you may want to change otherwise I would shoot and start with great brass that you can bump properly and start load dev with properly sized brass for your chamber.
Good luck either way a lot of good advise here.
I would use retumbo and 200 AB I get 3300 out of my gun and a three shot average of .6
for the 180 partitions I use H4831 and get the same result for a group but I have never shot it over my chrono. Keep us posted how your doing.
Always smile when your shooting its a privilege!