I've heard before that you can start a gascheck upside down in the case mouth of a straight wall case and then seat a plain base bullet as normal which will further seat the gas check and square up it up in the case as well.
I've been told this works as well as having the gas check fitted to the base of a gas check designed bullet as long as the gas check is held in place at the base of the bullet and not allowed to drop down in the case below the bullet which would be a major problem. Anyone here ever tried this with a case like the 45/70 or 458 lott ?

No, but I have used Dacron filler in the .45-70. That seems to provide some gas protection to the bullet. Won't work if your load is a full case of powder, obviously.

The black powder cartridge shooters are all the time using various sorts of wads under the bullet.

Yeah. I've tried it in a .45-70. Did not work as well as a proper GC bullet but did allow more velocity with accuracy than a plain base.

Thanks for the info.

I've done it with a .454 Casull and .45 colt, worked great in the .454 seemed OK in the .45 colt. In the .454 groups were extreamly small; some of the best groups I ever got with that revolver.

I only tried that on my 480 revolver, seeing how fast I could push my 310 gr plainbase bullets. What I found is that an errant gas check at 1450 fps will kill a chronograph Still haven't replaced it either.

Accuracy was so-so and I haven't had much opportunity to try it beyond that one application. I think in a case where you are considering getting a gas check mold and have a similar style plainbase mold it's a worthwhile cheapie way to check the application. I don't think the results will be as good as a dedicated gas check mold for that application.

I made dies to swage a GC shank on 35 and 41 cal bullets that work good. The upper part of the dies are .359 and .412 respectively so the bullet can't bump up over that. I haven't had any problems with those bullets and the GC's fit great. Mark