Long, long ago, Jack O'Connor wrote that factory ammo was loaded to a pressure and velocity, but not with any particular powder. I think that still applies. They may have a particular one they use, but odds are very high it comes in barrels, not cans, and each lot gets tested when it arrives and the loads worked up. It may not even be a powder you can buy. You can always pull one down and compare it to stuff you have on hand. If it looks like something you have, and IF the charge weight falls in the range of published data for the powder you're guessing it is, it might be worth working on, but I'd be inclined to just shoot what they make since it's cheap and accurate. Never tried it myself, but that blue box stuff has a lot of fans here.
