Well I finally managed to get som 255 gr cast SWC bullets for my USFA's in 45 Colt. They have 4 3/4" barrels.
The powder will be Unique. I opened a 4 lb keg today. I bought this keg in April of 1981, for $26.75...[yes 1981 ] So I thought I netter test it before loading a bunch, so I loaded one round with 8gr, 2 with 8.5, and one with 9gr.

All fired ,and the gun did not blow up.
My plan is to carry these guns while hunting here in Texas, and maybe other places as well.

I want one load, that hits close to the sights, that is powerful enough to keep a 2 legged varmint off of me as well as to kill a deer or wild pig if a close shot presents itself. This is not a primary Hunting handgun, but a Hunters handgun.
My old Lyman book shows 10 grains as a max load.
In a 5 1/2" Colt SAA 8gr gives 841fps, 10 gr gives 1011fps.
So I think I will load some at 8.5gr, and go up to 9.5gr and see which powder charge hits closest to the sights. This is a Colt SAA sized gun so I do not plan on trying to make it a 44 Mag.

My standard walk around field load for the 44 Mag has been for years a 240gr bullet over 9.2gr of Unique, and it has always served me well.

With the 4 3/4" barrel I do not see the need to go to 2400. And yes I know there are a lot of newer great powders invented since Unique, but I am NOT going to change, as I use Unique for other calibres as well.

This one load will be my General Purpose load.

IF I carry the USFA for Urban use while enroute to a hunt, I have a few factory loads that I will use. My favorites now are the Barnes 200gr Vor-Tex, the Buffalo Bore 225 Soft Cast Hollow Nose, or if I want deeper penetration the BB 225 Hard Cast Wadcutter, or the BB 255 Keith SWC.

I would carry the BB 255 Keith bullet if I was to use the USFA in Bear country. I have a few boxes of all of these loads set back, but my plan is to use my General Purpose load and CCI shotshells 90% of the time...

Your Unique will be a real nice load for the Colt. Around here, Unique is a staple powder for handguns as well as shotguns. The staple bullet is the RCBS 270 SAA

Since you are regulating the load to the sights, once you get there you probably won't need other powder suggestions. However, if you do desire to play, Hornady's 3rd edition has loads for the SAA with 2400.

Have fun!

Thanks for the info. I have used a lot of 2400 in my 44 Mag, and in a buddies 357 Mag. It is a great powder. If these loads do not shoot close to the sights I will give it a try.

I am thinking with a 255gr bullet I would load 17.5 to 18.5gr of 2400.

Well I had a chance to shoot the USFA Rodeo 45 Colt yesterday, with 5 different loads.
All but one had a 255gr commercialy cast 255gr SWC. These bullets are fairly hard, I cannot scratch then with my thumb nail.
All loads used a very old lot of Unique I have had since 1981.
The shooting was done off hand at 23 yards.
Here is how they shot.

8gr. shot 2 to 3" high and 1.5" left.
8.5 gr. shot 2" high and 1.5 to 2" left.
9gr. shot spot on elevation, and 1.5" left.
9.5gr. shot spot on and the best group by far.

The fifth load was a Speer 260gr HP iver 9.5gr of Unique.
It too shot spot on, and a group about the same size as the lead 9.5gr load.

Recoil was mild, and there were no high pressure signs, and the cases came out of the cylinders easialy.

These 9.5 gr of Unique loads will work fine for what I have in mind, using the SAA as a Field gun.
I am very happy with the group size, as well as how it hits to the sights.

However, I loaded up some loads with 10gr if Unique with the 255 gr lead bullet and the 260 Speer bullet, and will test them next time in the Rodeo, and I still have a set of the above loads to test in the Turnbull USFA, so I can see how the point of impact varies with the different loads in that revolver too.