The original 45 Colt load was a 250 gr. bullet at running 850 - 900 fps out of a revolver length barrel. There are many ways to safely duplicate this load. Brian Pearce of
Handloader magazine #291 published almost two dozen of such loads. I've fired several hundred of these loads in a couple of Uberti's and a USFA. My two favorites are 6.5 grs of either Red Dot or 700-X with either the traditional RNFP or a SWC, both weighing 250-252 grs. Some revolvers with a tight B/C gap and/or a longer barrel will get close to 850 fps with only 6.0 grs., while others will require 6.5 grs. Either powder will provide very accurate loads and at 6.5 grs. a fella can load over 1000 rounds with 1 lb. of powder.
I cast my own bullets, but got some commercial bullets by Missouri Bullet Company in on a deal. They were 250 gr. RNFP and shot very well out of my Uberti Frisco. Were I not a bullet caster, this is probably the bullet I'd use-
Here's a group fired using a cast bullet that duplicates the original and the Red Dot load-
And one with the 700-X load-
These loads using Red Dot or 700-X are going to yield around 1000 fps out of your rifle. If you want more velocity out of the rifle, use a slower burning powder such as Blue Dot, 2400 or 4227.
Regarding bullet weight for hunting, I personally wouldn't go under 250 grs. because as bullet weight decreases, so does penetration in flesh. A couple of seasons ago I shot a buck and a javelina with the above Bisley 45 Colt and I used a 265 gr. SWC. This year I'm going to use the Frisco and a 288 gr. SWC.
While we're on the subject of bullets, you're probably aware you're going to have to keep cartridge o.a.l. under 1.6" in order for it to function in your '73 rifle. This limits you to bullets whose length from the crimp groove to the tip of the bullet is not over .31", assuming your brass is the correct length of 1.285". The bullet on the left is a 252 gr. SWC and as one can see, it exceeds usable length while the bullet on the right is a copy of the original 45 Colt bullet and will function through the '73 rifle.
If you're a bullet caster, Lee makes a couple of .45 caliber moulds that cast a 255 gr. SWC (452-252-SWC) and a 255 gr. RNFP (452-255-RF) that will function through your rifle.
Assuming one gets a good mould (which is a crap shoot with Lee), both these bullets are quite accurate, or at least they were in my revolvers.
One other thing, a subscription to
www.loaddata.com will provide you with a plethora of data for the 45 Colt, data from manuals as well as Handloader magazine. Load searches can be sorted by caliber, bullet weight, bullet type, powder brand and/or powder type, and then printed.
Hope some of this helps.
CHT
Almost forgot-
Please note that is an 1973 design not a magnum revolver.
Remember Elmer Keith violently dissembled one with black powder. Of course he was using the equivalent of FFFFg powder or finer, and a humongously big heavy bullet but he wound up with a three chamber open top...or so the story goes.
If you want (need) an occasional big boomer get a .454 Casull and load down with .45 Colt cases for fun plinking .
Al least that is my thought I might be wrong.
Bunk
Depends. Standard's, Uberti's, USFA's and Ruger New Vaquero's are all larger than the original Colt's and have thicker cylinder walls, and by virtue of the fact that three of them are also chambered in 45 ACP whose +P factory loads run upwards of 23,000 psi, they sort of are magnums. But the 1873 rifles are NOT. All that said one can exceed the original load by around 150 fps and still be within SAAMI suggested parameters of 14,000 psi (
Handloader #54, #246, #275 and Alliant Reloaders Guide 2008)
The Keith event to which you refer was detailed in his book
Sixguns and he blew the loading gate off of his Colt when a cartridge case gave way. He had ground his black powder down very fine so he could get more in it, but blamed the problem on the old balloon head case that had corroded and weakened from being loaded with black powder.