I have a bunch of 280gr .454 SWC's I want to shoot in the 45acp cylinder of my NMBH. I want to load them to 900 - 1,000fps velocity.
I think I need to seat the forward driving band at the forward edge of the case mouth and apply a taper crimp since the 45acp headspaces on the case mouth. That means a compact amount of powder to avoid compressing the load.
I would appreciate suggestions for a 45acp load using this bullet in the Ruger NMBH.

I don't think I'm going to try this. I found a good discussion on another site that convinces me this can't be done safely.

https://castbulletassoc.org/fo...in-45-acp-revolvers/

Good call. 1000 fps can’t be reached at reasonable pressures with that long bullet in the tiny case.

Very doable and safe. I would size them to .452 though. I've seen proven tested loads with a 280 grain bullet to945 to 1093 fps using both Unique, 2400, and HS-6. The Speer manuals #8 and #9 have some healthy loads for the 45 Auto Rim using their 250 grain swaged bullets. I've shot 260 grain cast bullet from both my 1911 with a heavy recoil spring and also my Ruger Blackhawk with the acp cylinder. Not as bad as you may think.

I would work up from a bottom load and pay attention to the results as you go up in small increments. My cylinder throats on my Ruger 45acp cylinder are .452 so I see no reason that you can't load the bullets out further. Just work up slow.

As a side note I've fired those 260 cast bullets from a Ruger Old Army black powder revolver with some healthy loads of Triple 7 substitute powder. I know a fellow that worked at Ruger way back and he had to work up loads to insure the Old Army's were strong enough. Believe it or not Ruger used smokeless powder loads to test them with no ill effect. Contrary to some beliefs those revolvers are basically like a centerfire Ruger except percussion black powder.

Extensive lab tests have proved that in 45 Colt caliber, the full size Blackhawk cylinders are safe to 32k psi. Ruger has stated that the midframe 45 cal flattop is good to the +p 45acp limit of 23k psi. I think there is a good chance of meeting your goal in the large frame gun, but perhaps not in smaller flattop. I’m no authority, just passing on what I’ve learned.

the NMHB should easily do 23-K forever.
900 fps should be pretty easy to achieve with anything slower than unique and faster than h-110.
I'd probably look at something in the herco or BE-86 area since they don't need and don't mind a little bit of bullet contact.

Load data for 45 acp up to 260 gr bullets, here. http://stevespages.com/page8a.htm