modifying a mold

[hansg/Ups]

Has anyone modified a mold with clay,plaster of Paris,etc.?
I'm interested in making a couple of heavy weight full wadcutter molds for a 45Colt and 45/70
revolvers[Redhawk[long chamber allows 1.800"o.a.l.] and BFR respectively]. A 300+gr full wadcutter for the Redhawk and a >=400gr full wadcutter for the 45/70,even at modest velocities with wheelweights, ought to really ruin a critter's day within ~60 yards.
Thanks.

[StrawHat]

I have never altered a mold as you suggest.  I have experimented with the cast bullets.  If you want to end up with a 400 grain WC start with a 500 grain round nose and cut off enough until it is 400 grains and flat.  This is the easy way to experiment.  If you do not need a lot of them, once you get the correct length, you can make a kig to hold the bullet and stop the cutting at the correct length.

Another method is a bit costlier but also gives better results.  Get a swage die built to your final shape and weight and swage the cast bullets to shape.

I have used full WC bullets from 38 and 45 caliber handguns, they do hit with authority when launched at 900 - 1000 fps.  I have tried similar bullets from a 45-70 and ended up going back to a RNFP profile for hunting or even better (for the ranges you mentioned), the Gould bullet (Lyman 457122) a 330 grain hollow point designed for the 45-70 and hunting.