If I was gonna build one, I'd start with what you used. Those old ones with 2 3/4 ONLY chambers have a much shorter stroke than the later ones.
A man NEEDING to use one is gonna be pretty excited and it's easy to short stroke the newer ones.
It's one thing to hear the "click" as the firing pin strikes air and you watch a cock pheasant fly on off.
Damn sight worse when you REALLY need it to shoot a second time.
