Maybe try the marlin firarms pageMH & look for nef(new england firearms) H&R single shot rifles.? they come in many(30/06 ,280. 270.25/06,243 308.7x57 etc etc cal,s i ave the 223& 45.70 & you can buy extra barrels& convert to a shotgun or other rifle . there about 200- 225$ or so i think.
Extra shotgun basic barrel $35.00
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goodluck hope ya find something u like somewhere,& have fun shopping <Mh