Originally Posted by Taterhead
Go with 300s. There is nothing about 10mm auto that requires mag primers. I do use 350s for a couple of my pet loads with Accurate no. 9 (A9). A9 is about the slowest-burning powder suitable for 10mm Auto. It doesn't necessarily need mag primers. I did workups with mag primers years ago and I have loads that work great. Standard primers would probably work fine too. I just have not fiddled with re-tests since I have loads that work very well.
Bottom line is that mag primers can alter the burn speed of powders and impact presure in an undesirable way. All of the powder manufacturers that I know of call for standard primers (or in-between Winchester LP) for 10mm. Speer calls for mag primers for certain powders, but they are a rare exception in the various 10mm manufacturer data.
Thanks Mr. Taterhead. Speer is exactly where I saw the #350's referenced. I've seen them in some rifle loads in Hodgdon 2012, too (for BLC2, I believe). I ordered 5# of BD and 1# of A7, W231 from PV for new 10mm. I already have kegs of powders for my .40 loads like A5, Power Pistol, Unique, WST (favored in that order). If mem serves me right, PP is the slowest but i don't think it'd warrant LPM's except maybe for experimenting. Don't think I'll b experimenting too much for now in 10mm. I've only been handloading/reloading for about a yr. but have gotten into it heavily. Precision Rifle forces you to do that ;-) It's fun to me.
So have you used any of those powders above I mentioned for my .40 loads in 10mm?
Seems most folks use BD.
Thanks again for sharing.