I had one for several years and did a lot of shooting with it. Selling that gun is one of my biggest regrets.
Loads:
These loads were developed in the late '70s to early '80s. All loads used revamped Lake City .308 brass and CCI 350 primers.
I strongly recommend you reduce these loads AT LEAST 10% to start. They all worked well in my gun, but powders may have changed somewhat and I'm sure the bullets are different. WW296 powder was best, and I tried a lot of different powders. H110 was pretty close.
180 gr Sierra JHC/31.0/WW296/CCI 350/1990fps
240 Hornady JHP/26.0/WW296/CCI 350/1640fps
Lyman 429421 cast/22.5/WW296/CCI 350/1580fps
265 Hornady/22.5/WW296/CCI 350/1510fps
All loads were fired through an 8 1/2" barrel.
With the 180gr Sierra, anything under 30.0 of WW296 wouldn't function in my gun. I didn't use the listed load except for chronographing. My notes say to try 31.5 or 32.0 gr of 296, so I guess the pressure was pretty moderate. A load with 29.5 gr of 296 gave me 1880fps, but wouldn't push the bolt back far enough to pick up the case rim. The gun would extract and eject the fired case, but recoil would tip the next round nose-up and the bolt would hit the case in the middle.
The original .44AMP, wasn't equipped with an accelerator (designed to give the barrel extension a little extra "kick" to the rear) like the .357AMP in order to reduce stress on the barrel lug and the bolt. The result was that the gun would function only with pretty hot loads, especially with light bullets.
I used the 265 gr load on two deer. Both deer went down with one shot and both rounds penetrated all the way through. I hit the second deer just to the right of the breastbone and the bullet came out just to the left of the butt. That bullet wouldn't expand on the sidewalk, which is just what I wanted.
Get the right dies. .44 Mag dies will not work. The case isn't the same shape at all.
Good luck.