can you get measurments of other 50-70 rims,made by difrent makers or maybe othes could post thickneses of difrent brands that fit in there rifles 56-50 & 56-56 rim thickness was the same in original cartriges ,i will start Bertrum Brass 50-70 cass modified to fit in a original 56-50 carbine,rim thikness 0.065 ,when proper thikness is worked out and compared to youse Buffalow Arms casses can be checked to see if they are the right thickness if they are not i am sure they would fix the problem ,i just went back and looked at your earler post stating the difrence in rim thickness of the 50-70 brass and the starline 56-50 brass was 0.005 to me your photos look lick the cass is out further than this sugesting your rim diameter is to large, try puting a cass in the chuck of a drill and slitly reduce the diameter,i think this may fix the fit if not you can reduce the thickness whith a safe edge file on the front of the rim by turning in the cuck not the best way but sure beats slowly doing it by hand,another thort looking at original rimfier cartriges they have a radious on the edges of rim ,try puting a slight bevell on the leading edge of the rim and see weater this seats the cartrige deeper if this works it will save you a lot of work