The .45 calibers were not real popular until just a short time ago. Many of the older models had some twists and rifling that were just real hard to tune. Plus the fact that a .50 caliber loaded down will do basically the same thing as the .45 caliber, many shooters did not see the need for them.

Now there are .45 caliber shooters out there, and some great rifles. White rifle makes a .451 caliber that shoots large conicals with extreme accuracy. Knight and Thompson center went through that "right twist" stage of development as well as the other companies. There are some real good .45 caliber rifles now available on the market.

http://www.prbullet.com/s45.htm here is some information and a sight that might be able to help you with finding the right load for your rifle. Email them. They will suggest some bullets that might shoot very well out of your rifle.