DAVIS125

I'm trying to cast small pewter medallians with detail similar to a state seal; an image with lettering around. I've tried rtv molds but they provide no detail, maybe a gas venting problem? Also tried sand mold which was a bit more successful but left a grainey texture and some detail loss. I have no high temp facilities at this time so I'm limited to low temp alloys. Any suggestions or comments on how to accomplish this project? Thanks,