AA8700 in a 45-70 as a BP Substitution

[jonp]

I'm going around the horn on finding data for my 43 Spanish. My major concern with this old rifle is pressure as it's a BP rifle. A data sheet I got from a member here lists AA8700 data of about 56gr or so of AA8700 but notes that this is a 45-70 loading minus 10% for safety. There is no pressure data listed. I have some, well maybe 40lbs, of WC860 which Jeff recommends using AA8700 data with.

I looked up an old thread on this site about 45-70 and AA8700 and found this loading:
420gr. (Ly 457193) 54.0 8700 1025fps 60.0 (Max trapdoor) 1165fps 11,700psi (compressed load). 24" test barrel

The pressure sounds fine to me as it's in the Black Powder range but I would like opinions on this. Safe load for the Rolling Block?

[rfd]

aa8700? i don't see that powder listed on their website.

one of the better, if not the best smokeless powder loaded for the .45-70, for trap door loads, low pressures and great accuracy is aa5744. i've used that lots before moving on to bp.

[gunauthor]

I tried 8700 and found it to be very wasteful with LOTS of unburned powder.

[jonp]

I tried 8700 and found it to be very wasteful with LOTS of unburned powder.

you did notice the part with "40lbs of powder", right?

[bruce drake]

I'm ok with loose grains in the bore to be blown out with a tube if the resulting load of powder has low enough pressure and accuracy for my 50-70 Trapdoor.

[rfd]

8700 must have been like 5744 - loose grains after firing, not a problem at all.

[Freightman]

WC 860/ WC 872 = AA8700 in pressure, use it in my 45/70 RB 57 gr with a 3cc LEE scoop of 3031 as a kicker 1250 fps with a 405 HB boolit. No pressure signs and you cant put enough of it in a case to get pressure signs. 860 is 50 BMG powder and 872 is 20mm powder