Have any luck with these? 45-70 in particular.

No problem at all, they will shoot great.
The Ranchdogs shoot well and if you want something with more stopping power check out Beartooth.

I have a Marlin 45/70 in Microgroove. I have had very good result both in velocity (no or negligible leading) and accuracy. I have used several commercial offerings and have settled on, for elk hunting, the Beartooth 425 gr gascheck sized .460.

Reason I ask is I bought some 405 gr casts and my groups have been terrible, some going through side ways at 100 yds. This gun shoots 1 1/2 " groups at 100yds with jacketed bullets and 6-8" groups with casts. Need gas checks?

I found out early that my 45/70 with microgroove bbl. didn't like cast at .458. But when used as cast at .460 things took a turn for the better.And with out gaschecks too.

the cast bullets, do your bullets have a flat base or are they "boat tailed"?

A buddy's unit does very will with cast/gas checked slugs. Like near 1 moa. If one is running smokeless, he should be using checked slugs.

I've had good luck with cast bullets in the micro groove barrel, provided the bullet is slightly oversize. With groove diameter cast bullets they shoot well with low velocity plinkers. For full power loads, they work best when a couple of thousandths over groove diameter.

My Lyman and RCBS molds cast a flat base, but I also shoot a local commercial cast beveled base 350 gr. as cast at .460 (unsized) which does well out of the micro-groove bbl.

With out gas checks?