The manufacturers have dozens, perhaps hundreds, of powders not availible to handloaders. Factorys use pressure testing and a specified formulas in the powders they buy. They test and adjust powder volumes to match each 1000# lot they buy. Most of the time when a powder is not offered in canister lots to reloaders it's because the lot to lot uniformity has too large a variable as produced. This makes it nessesary to pressure test and adjust each lot which the manufacturers do anyway. As an example I no longer use H-380 because it veries too much when loaded to top velocities in my varmint loads. I came up with some really great shooting loads with it only to find that the next time I bought some the velocity was down 200 fps and it didn't shoot for crap. The third lot gave sticky bolt lifts all with the same component set other than the powder lot. I moved to H-414 and haven't had any problems since.
In answer to your question, Yes they have powders we don't but for good reasons.
In your 300RUM try some RL-25. I load it in a 7.82 Lazzeroni and get 3840fps with a 165Barnes TSX.
