I think the pinfire slots would be too narrow on most guns. The nipple diameter is .168" for a #11 cap and the slot on a pinfire at a guess is around .1 or a bit bigger. On the smaller pistols the hammer is fairly weak and I found that using an upside down cap in a cylindrical cavity, they would not fire. Sometime I hope to try making a shell with a square cavity for the cap to sit in and hopefully that will work.
cheers mooncoon