You need to remember that for the time frame you suggest - it's the 'cartridge' weapon that'd be unfamiliar to most.
This proposed category falls between 'Buckskinner' and 'NCOWS shooter' with no secure footing in either.
If you're serious about APS - pick one and establish guidelines, stick to them and stop trying to straddle a fence that's just going to wind up muddying the waters insofar as your time frame is considered, if you try to accomodate everyone's ideas and fancies.
NCOWS does just that - and beyond reviewing what's approved for weaponry - it manages quite well to keep folks outfitted and shooting happily within their specified era, without any attempt to join an ever-increasing arms race - even allowing pretty much everything you're proposing, so long as you can document how you came by the gear used by your Impression.
If your cut-off is roughly 1865 - then cartridge weapons were 'not' common, and given wartime production, new percussion weapons would've been in short supply, since most arms makers were attempting to fill contracts - early percussion guns and single-shots would've proliferated - despite the advent of the aenemic Paterson, and hard-to-find-at-the-time Walker.
The Navy Colt and Pocket Model would've been cutting-edge - along with the odd Dragoon.
Good Luck!
Vaya,
Scouts Out!