Tim, this is kind of directed your way. Alliant powder recently came out with RL-10 in their series of numbered powders. 10 is about 13% slower than 7 and in the burn rate scheme of things it is pretty much the same as WW748. The extra 10" of tube that we BC bloaks pack around has been the subject of much debate as far as any extra velocity gained is concerned. I read somewhere in this forum that you, Tim, is or was on the hunt for a slower powder than 4198 to take advantage of the extra tube on Bc`s. It might just be 10 as the 13 % slower burn efficiency would be well used in the longer tube. 10 is probably a high energy powder much like 7 and should do well in longer tubes, below you will find some data from Alliant, actually they got it from Speer and will give one a base to start from.
300 gr. Speer-start 48 gr-1946 fps. max 52 gr-2065 fps
400 gr Speer-start 40 gr. 1554 fps. max 44 gr. 1720 fps
Speer apparently worked up these somewhat conservative loads and they are playing it safe, They probably are mid level 2 loads, there were no pressure figures given. What really got my attention concerning this powder is a post somewhere I read that was from a guy shooting a BC and using this powder, his result is as below.
300 gr Sierra jacketed-47.6 gr RL-10 2094 fps 32" BC tube.
Of interest here is the extra 148 fps velocity from the longer tube burning off essentially a starting load of 48 grs. Over at realguns.com there is a very complete 5 part lowdown article on the 45-70 called" The Model 1895G & Handloads For The 45-70". The fifth installment goes over in detail all the loads, one might notice that RL-10 gives an impressive performance, again, no pressures but for sure these are smash you in the face loads!
Ok I know about the vagaries of handloading and how one gun shoots completely differant than every other gun in the world but it would be interesting to do a report on this powder in a BC, who knows, there might be a gold mine there!
Thanks, see ya
Richard