I really don't know why anyone uses any other powder than AA5744 in these big, low pressure cases. According to Accurate Arms, this powder was developed for the 45/120 case, I think they found an existing powder and it worked well, regardless of advertising hype, it works well.
You can see the velocities I measured during load testing and in several other 45/70 rifles.
45/70 Martini Henry 26" Shilen Barrel
Code:
405 LRN 26.5gr AA5744 R-P cases WLR
29-Apr-04 T = 80 °F
Ave Vel = 1294
Std Dev = 14
ES = 40
Low = 1274
High = 1314
N = 15
Group Size Very . good
405 LRN 27.0gr AA5744 R-P cases WLR
24-Mar-04 T = 70 °F
Ave Vel = 1284
Std Dev = 23
ES = 80
Low = 1263
High = 1343
N = 12
405 LRN 27.5gr AA5744 R-P cases WLR
15-Apr-05 T = 75 °F
Ave Vel = 1363
Std Dev = 25
ES = 97
Low = 1298
High = 1395
N = 20
Group Size good offhand at 100 yards
Winchester BPCR M1885 30" Badger barrel
Ladder Sights: 5 graduations per 1/4 inch major.
1/4 inch major is 25 MOA, 1 grad is 5 MOA, 1 Vernier is 1 MOA
Code:
405 LRN 27.5gr AA5744 R-P cases WLR trimmed 2.085"
29 May 2010 T = 89 °F
Ave Vel = 1324
Std Dev = 9
ES = 26
High = 1338
Low = 1312
N = 6
I have not slugged the barrel of this M1873, but it leaded something awful till I applied a huge amount of external grease to the bullets. I think the barrel is large compared to my commercial cast bullets.
M1873 Springfield Trapdoor 1884 rebuild 27" sight radius
Code:
405 LRN 27.5gr AA5744 R-P cases WLR trimmed 2.085"
14 Aug 2014 T = 78 °F
Ave Vel = 1302
Std Dev = 11
ES = 26
High = 1315
Low = 1289
N = 5
First round 15.5" high, rest, 19.5 to 23" high at 100 yards
Ballistic calculator: 100 yd zero, 25" drop at 200 yds, 82" drop at 300 yds
405 LRN 27.5gr AA5744 R-P cases WLR trimmed 2.085"
Heavily greased with Lubriplate 130A
14 Aug 2014 T = 78 °F
Ave Vel = 1346
Std Dev = 15
ES = 38
High = 1371
Low = 1333
N = 5
If you use commercial cast bullets, I recommend you grease the heck out of them. Mine fouled badly until I externally greased them. Messy, but it cut out the lead fouling.
You can see that I used so much grease that grease was extruded down the sides of the shell casings, into the action.
Ungreased fired cases on left, greased, fired cases on right. Absolutely nothing bad happened outside of grease in the action. Considering the lead fouling reduction, I can live with that.