Fire-forming

I have a .25 Ackley Krag Improved.  This is the full length .30-40 Krag necked to .25 with case blown out nearly straight with a 40 deg. shoulder.  Last fall I worked up jacketed bullet loads using Speer 87 & 100gr. bullets for accuracy benchmark.  prior to this I partially formed cases in #1 &#2 RCBS case forming dies..leaving partially formed shouder a tight fit as action closed..as well as having bullet snug into lands.  Cases formed perfect. This Spring I have begun cast bullet experimenting and have found the NOE 100gr. f.n.g.c. giving around 3/4" groups at 100yds. using 18.0grs. H4227..but with fliers..more work yet.  I would like a few more formed cases & was wondering if the above load would fully form a case?  I have heard of using Bullseye and cornmeal..but that big case body funneled down to a sharp 40 deg. shoulder causes concern.  Any suggestions?   I can increase the H4227 charge up to 20.0 grs. or so without leading...but no accuracy either!