Smoke;

Correct.

Read my previous post Re: shims. With the existing .303 zig-zag, they might help.

I do believe, however, that quite a number of single-stack .45-70's exist out there that feed OK. Maybe try different parts? I also wonder if you could get a spare magazine spring, cold cut a length and add it to the top of the .303 spring, rivetting it either to the bottom of the follower or to the top of the whole mag spring, this to provide additional forward support.