I've used all types of small rifle primers as the 7-1/2 primers were very hard to find around my area back then. When I did find some last year, I put about 10,000 of the Remington 7 1/2 away and will use them as Mr. Casull said

The 300 Grain XTP mag is definitely my FAVORITE bullet in my FA 454. with that bullet I'm getting about 1615 and amazing groups at 100 yards. On game, it is devastating!! I have shot deer at 110 yards that the bullet entered the front of the brisket and traveled lengthwise through the deer exiting the opposite side hindquarter. Only movement was straight down

That bullet is very hard and don't expect much expansion from it if any. I wouldn't try to max the load out in that gun. I don't know if you have ever taken any game with that handgun but I think you will be presently surprised to find out how effective the 45 caliber slug is at moderate velocities. It will allow you to enjoy the shooting much more and you will never know the difference on the game that you shoot most likely. Full house loads are fun here and there but the lower power ones are MUCH more enjoyable. I rarely shoot the 1600+ loads in my FA anymore. Its just not needed. In fact, I used that FA this past week to shoot a 225 pound Merino Sheep at 95 yards. The sheep dropped at the shot and never moved. The load that I used may shock you....it was a bullet cast relatively soft from a RCBS 270 SAA mold over a mild 12 grains of HS6 in 45 Colt brass. That load is traveling about 950 fps from that revolver. So, bullet weight and caliber account for a lot when hunting with sixguns. These guns don't have to be run full bore to be effective. Good luck with the 454!! Enjoy it....GS