To be a reasonable conversion candidate, a cartridge should show some obvious characteristics.
- It should have a case head diameter of about 0.50 inches, with perhaps a few thousandths over, but very few under. A sizing die can decrease the diameter to the brass, or the brass head can be turned a bit at the head region.
- The case should be sufficiently long to achieve easily a final length of 1.700 inches.
- Cases should be relatively inexpensive, and readily available.
[1] 45-70. In this straight-walled case, the head is nominally .504" max, length is 2.105". It's available currently; Midway has it on sale at 70 cents each. Conversion to 450B would require turning the case head to remove the rim and to form the 450B rebated rim and extractor groove. Cutting to length is not a big chore. My sample 45-70 case has pretty thin walls, so the converted cartridge may not require reaming to produce usable neck wall thickness. If the case is a little larger in diameter than the 450B case, the 450B FL resizing die will reduce it easily. If the case is larger than 0.500 just in front of the new extractor groove, the resizing die may not reduce it at that point; a light lathe cut will bring it into spec.
The web of my 45-70 sample case is about 0.17" thick. The web of sample 450B Hornady cases is about 0.20" thick, so converted 45-70 cases may not be as strong as the 450B case. Cuts for the extractor groove should lie within the length of the web. However, it would be wise to section lengthwise a converted 45-70 case and compare it to a sectioned 450B case to see any obvious case head weaknesses.
[2] 45-90. These cases are dimensionally like the 45-70 except they are a bit longer. The same procedures as with the 45-70 should convert them to 450B dimensions. They are available, and cost about $1 each.
[3] 376 Steyr
This cartridge has a case head of 0.506", and a case head to shoulder length of 1.89. It's available currently at about $1 per case. The neck and shoulder would have to be amputated, and the rim and extractor groove turned to proper dimensions, like the 7.5x55. Like the two 45s above, the FL 450B sizer will bring most of the case length to proper dimensions. If the portion of the head that can't be formed by the sizer die is too great in diameter, a gentle touch with the lathe can bring it down to 0.5000. Fire forming may be needed, and perhaps reaming of the neck if the case walls are too thick.
If there are other candidates for reforming that meet the criteria of head size, case length, and availability, then posting these others will be helpful.
--Bob