I just started reloading .45, but I found it very useful just for this reason to buy the "Loadbook" advertised in Midway for the caliber in addition to one of the comprehensive, all-caliber loading manuals. There's no use buying the whole loading book for every bullet company.
The comprehensive manual (I have the Speer) has essential info on technique, but the Load Manual has the actual data for that caliber from a variety of manuals, without all the cautions, safety notices, and company histories. It's published by Loadbooks, U.S.A. and is available in many calibers.
In .45 it has info from six bullet makers and seven powder makers. It has the Hornady loads for a 185 SWC, though I don't see where it says whether it's plated or not. (The Hornady section says they only make one kind of 185 grain SWC.) It's Hornady # 4513, and lists a wide variety of loads from 750 fps to 1000 fps. You don't say what powder you're using. I use WIN 231, and for that powder it lists 5.4 grains for 800 fps up to 6.3 for 950. It doesn't have Rainier bullets. Since the book has powder manufacturers as well, I looked under Hodgson and Winchester, and both list several powders and loads for jacketed SWCs.
Just out of curiosity raised by your intitial question, I compared the loads I just quoted to you to those for Sierra 185 FPJ and WIN 231 and found that they list 5.4 as 800 fps and 6.3 as 950, so one result is the same and the other isn't. So there is a small amount of variation depending on bullet manufacture, which was your question. Or maybe it's due to the fact that there were two different test weapons. Who knows?
I guess the answer, as always in reloading, is be cautious, start low, and slowly work up while watching for signs of excess pressure, not exceeding the maximum listed load.