As far as I am concerned Cooperville can copy, redesign, build and repair any firearm available before 1960 that is not specified in a higher tech bracket. Cooperville at tech level D can build the bolt action 1903, the M1 Garrand, even the M14 but not the AK-47 assault rifle. They can build the Thompson SMG or the MP5 SMG but not the M-4 carbine. Shotguns, both pump and auto, built from 1880's until fully automatic versions appear are permissible. Cooperville cannot build the bazooka nor the 57mm recoilless rifle even though both were built in WW2 because those items (and the AK-47 assault rifle) are listed as tech level C.
Tech level D+ communities are fairly rare, occuring only 17% of encounters. As such they need more development than the village of 100 using breech loading, cap "Sharps" rifles.
In the end it is your game, as long as you can find a reasonable explanation it fits.
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