I used to have .45 Colt and 45-70 inserts for a Mk. lV which were made by Ace Dube in Anchorage, Ak., and I bought through Bullseye Reloading in Fairview, Ab.. They were both made to the same length as a 577-450 case.
As Martini chambers can vary somewhat, I found that I had to fit each insert to my rifle, which was quick and easy with a drill press and swiss files.
I shot the .45 Colt with soft cast bullets as large as I could drop them from the mould. They worked quite well with medium loads of smokeless, and would push out of the insert easily after firing.
I shot the 45-70 with both blackpowder and some equivalent smokeless loads, using the Lee hollow-base 405gr. bullet.
They also shot reasonably well, but as the whole 45-70 case went into the insert with only part of the loaded bullet exposed, the expanded brass stuck in the insert at firing, and was a pain in the ass to get out using only a dowel push rod. You can avoid this by lightly oiling, or leaving some case lube on, the 45-70 brass BUT are likely increasing back pressure on the breech block.
I found both inserts easy to use, and I felt that their cost was more than offset by the greatly increased fun quotient of being able to use the rifle without the problems which I sometimes found with 577-450 (eg. re-annealing brass, etc.).
Regards, DaveF.
