I have heard good things about varget in 45-70 as well. But will start with what I have on hand. My other options will be H-4895, and possibly benchmark ( not sure if can use with this weight of bullet at these pressures). I have load data for benchmark but only for 300gr bullets and when heavier bullets are used it is at trapdoor levels. So have ruled it out for now. I also have SR-4759 but it will not give the velocity I would like. I have trail boss which I will use in this caliber but not with these bullets. I will make up some plinking/small game loads with it and most likely a 300gr bullet ( or what ever I find a good deal on).
I have one vote against 4198. I am leaning away form H4895 because of what I read in Pet Loads with inconsistencies and below average accuracy. I have had similar problems with it making light loads for a military bolt action bench rest match I like to shoot in (however, it did do fine at full house loads), which is were the SR-4759 came in. But I will try it if the H-4198 does not work.
As I was looking at data for Varget, I found what I may try if I do have to buy powder. Ramshot X-Terminator gives far better velocity than anything else listed. The starting load I have is 20 fps faster than the max I have for H-4198 and the its max is about 175 fps faster than H-4198 this data was all from the ruger #1 so should be somewhat comparable.
MGM
Thanks for the warning with H-4198, even thou I have it on it hand I have not worked with it yet. However, I always work up slow probably slower than most as I always check several sources and find several max loads which reminds me every rifle is different. My last testings with my 6mm-284 took me three range trips to get all my loads testing partly because I was going at 1/2 grain increments and partly because it was so hot and barrel cooling time was long.