In that gun...
or any other big-framed Ruger, I'd start that bullet over 13 grains of HS6. That has been sort of a magic charge for me and it has worked wonderfully with every 250-255 grain 45 Colt bullet I've tried it over, always getting around 1050 fps from a 5 1/2" old Vaquero. Accuracy has been all this shooter could use, sandbagged or not.
I understand the Unique thing. I'm the same way about my go-to pistol powder, W231. I am a minimalist reloader for sure but HS6 is great for the kind of loads you're talking about.
Complete thread:
- Load Info .45 Colt RCBS 270 cast? - 
woody, 
2012-09-01, 12:08 
- Load Info .45 Colt RCBS 270 cast? - 
Hobie, 
2012-09-01, 12:44
- Load Info .45 Colt RCBS 270 cast? - 
woody, 
2012-09-01, 13:00
- Load Info .45 Colt RCBS 270 cast? - rob, 2012-09-01, 14:54
 - Load Info .45 Colt RCBS 270 cast? - 
Hobie, 
2012-09-01, 19:13
- sounds about right. - woody, 2012-09-01, 20:04
 
 
 
 - Load Info .45 Colt RCBS 270 cast? - 
woody, 
2012-09-01, 13:00
 - Load Info .45 Colt RCBS 270 cast? - Bj2, 2012-09-01, 14:29
 - Don't know what kind of gun you're using . . . . - 
RangerBob, 
2012-09-01, 14:37
- Ruger Blackhawk - 
woody, 
2012-09-01, 15:49
- In that gun... - Sarge, 2012-09-01, 16:09
 
 
 - Ruger Blackhawk - 
woody, 
2012-09-01, 15:49
 - Load Info .45 Colt RCBS 270 cast? - Dave B, 2012-09-01, 17:51
 - Load Info .45 Colt RCBS 270 cast? - Charles, 2012-09-01, 18:42
 
 - Load Info .45 Colt RCBS 270 cast? - 
Hobie, 
2012-09-01, 12:44