@BCRider great response, thanks for the thoroughness of your information. For sights, I was thinking of a 3-9 scope on my the centerfire, with see-through rings so I can use the iron sights, which are set for the rimfire. So as long as my mounting doesn't destroy their accuracy, I'd have a rimfire with irons (good for 0-50yd on small game) and a centerfire with scope for the rest. As far as action weight goes, that is definitely a concern. Since this is intended as a bush gun, I'm concerned my design will end up being a 12lb monstrosity that is too unwieldy for the bush. Keeping the barrel short is step one to reduce that. Since my design will place the action of the .22 where the forestock of the centerfire normally is, I gravitated towards semi-auto for simplicity of operation, since racking a bolt or lever action that far forward could be difficult. A single-shot like a rascal is interesting... It doesn't maintain the repeat-shot ability that I have in mind, but if it is the only way to keep the weight down enough to make this thing practical, then that might be the way to go. Thanks!