A time-honored hot load for modern Colt SAA is 250 or 255 grain cast bullet with 10 grains of Unique.
It should be noted that this particular recipe will exceed the standard operating pressure for the 45 Colt and that it may not be safe for some guns.
I've never tried that load, I have just seen it listed in reloading manuals and online with the comment that it's safe in post-war Colt SAAs but not to shoot them in pre-war guns. I wouldn't shoot it in a SAA but it ought to be a good economical "magnum-ish" load in a Ruger or a Casull.
I've been using 10.0gr Unique under a 250gr SWC as my "standard" .45 Colt load for over 30 years. it has been listed in the Lyman manual for generations. Its in my 1970s book, and were I to dig it up, pretty sure its in my 1950s book. Yes, it IS a max level load, tested in COLT SAA's. And, like any top level load, it should be worked up to, in YOUR gun, with YOUR components.
That load gives around 1000fps from the mid barrel length guns (5.5") a bit higher or lower due to individual guns factors. I wouldn't put it in a pre-WWII Colt, either. I wouldn't be concerned about working up to it, in a post-WWII Colt SAA though. Even though it is a bit over SAAMI working pressure for the .45 Colt, its not near blow up pressure levels, and do remember that the SAAMI working pressure is for ALL .45 Colt guns, including blackpowder ones. Colt made the post WWII SAA in .45 Colt and .357 Magnum, so I'm personally not concerned that SLIGHTLY exceeding SAAMI spec is a blow up risk in those guns. Besides, I don't have any Colt's, my .45 Colt's are Rugers (and T/C Contender) and they don't notice 10gr Unique as a hot load,
That load is not a "Ruger Only" load, those loads are even heavier. It IS a top end load in a Colt SAA, and I wouldn't use it in any of the top break .45 Colt's out there now. (and NEVER in anything made by Armi San Marcos!)
It does just a hair under 1100fps from my 7.5" Ruger Blackhawk, and while noticeably more than the standard factory load, its enough below full "magnum" loads that it is not uncomfortable to shoot a couple boxes in an afternoon, out of the big Ruger. From a smaller gun like a Colt, (or New Vaquero) it's a bit more brutal.
But its also not the load to use shooting LRN 230gr .45ACP bullets. I would use 7.5gr and not think of going over 8gr, there's no point and that bullet isn't well suited to heavier loadings.
Not sure what kind of accuracy you'll get out of a Raging .454 gun. You can drive the soft slugs too fast for accuracy, and bad leading could result. Keep the velocity down in the 8-900fps level and you should have good results, and recoil in the big heavy guns will seem light.
Here's a new term that means nothing to me; "softball" when discussing lead bullets.
While I can't be certain how the OP's bullet maker means it, "soft ball" is not a new term, its an old one. Military ammo is "ball" because originally, it was a round ball, and the term was just carried on when balls became bullets. "Soft ball" comes from the early days of FMJ ammo, when jacketed bullets became "hardball" and lead ones "soft ball". Hardball stuck with us, soft ball (as a term) faded into disuse and obscurity. It is, however entirely proper to call any non jacketed slug with the "ball" bullet profile "soft ball", though I wasn't aware, till now, that anyone was actually still doing it.
