I have a Blackhawk with .45 ACP and .45 Colt convertible cylinder. From all I've read, it does not handle the "Ruger-only" load for .45 colt.
If the Ruger can't handle them, doesn't it seem funny to call them "Ruger-only" loads? How old is your gun? Unless it was made in the past few years, I'm pretty sure it can handle the "Ruger-only" loads. As for those, looking back through my reloading manuals:
The old Hodgdon manual from the mid-'90s has no "Ruger-only" loads. There is no write-up for it, but
Hodgdonreloading.com has a section for "Ruger, Freedom Arms, & T/C Only".
Sierra 5th Ed. (© 2003) has a section for "Ruger, Colt [Anaconda], Dan Wesson, Freedom Arms". The 4th Ed (mid-late '90s) has the exact same write-up. It says in part: "
... renewed interest has resulted in the development of several new revolvers of modern design able to withstand much higher pressures..." Sierra's test gun was a 7-1/2" Blackhawk.
Speer Reloading Manual No. 12 (© 1994) states:
... The Ruger Blackhawk and the T/C Contender can both handle somewhat higher pressures than traditional .45 Colt revolvers... The loads Speer developed are between 20,000 and 25,000 psi... These loads are intended for use only in the Ruger Blackhawk and T/C Contender... Speer's test gun was a Blackhawk.
Hornady's 4th Ed. (© 1991) states:
The following data is to be used only in the T/C or the Ruger Blackhawk...
To add to that, I've had a Blackhawk .45 Convertible for the past 20-some years, and it has never had any issue using any of these "Ruger-only" book loads.
But now having written all of that, it seems Ruger has muddied the waters a bit. They released their "New Model" Blackhawk 45 in 1974. Some of the "old model" guns were built on a slightly smaller frame, but the .45 was on a full-sized frame that could handle magnum pressure loads. Later on, Ruger released the Vaquero, which could also reportedly handle the "Ruger-only" loads.
It seems in recent years, Ruger has gone to a small frame Blackhawk, but still called the "New Model" and hence some of the confusion. And it's not really easy to tell the difference right off. I just bought a 1965-vintage Blackhawk, and the difference between that and my .45 are very subtile. I had to break out the calipers to verify the differences (the cylinder is .050" smaller diameter, for example). Some people on the Ruger Forums refer to this original size as a "medium frame". So is the "New New Model" .45 on the "small" frame?
Or are the Flattop models the "new new model", which are the only ones that can't handle the "Ruger-only" loads?
What a hassle. Maybe it's easiest to just get a Super Blackhawk in .44 Mag and be done with it.
eta: Some info on Blackhawk frame sizes
here. That discussion doesn't get into loading for the .45 model, though.