I was puttering around online recently and found some folks that do Enfield conversions, including .45ACP, 7.62x39 and .45-70. They also do integrally suppressed De Lisle style conversions.

I asked if they could put one together in .45-70, and they said it was doable, but they had some concerns.

Specifically, since .45-70 normally runs on a slow burning powder, getting unburned powder into the suppressor could potentially result in some catastrophically bad things happening.

If I was able to put together a subsonic load that would be almost totally ignited by the time it reached the point in the barrel where the venting for the suppression happened, it should be safer. I am a newbie when it comes to reloading, though, so I wanted to see if any of the more experienced folks here could tell me if such a load would be feasible?

It would be 8"-10" of barrel before the porting starts.

Check out the 458 SOCOM Forum Bunch of those guys run suppressed and ballistically the SOCOM is pretty close to 45/70.

The 45-70 can operate well on faster burning powders. You just have to be careful assembling the loads.