Rifles- must be converted to US made guns FIRST (10 imported parts maximum)
Then you can now add a folding stock, flash hider, bayonet lug, pistol grip
The only rifles that are US guns off the shelf are the Veprs and SAR rifles. Saigas have to be converted.
Shotguns- Must FIRST be converted to US made guns
Then you can now add a pistol grip, folding stock, and have magazines in excess of 5 rounds
Rifles that are not US parts compliant still fall under the 89 ban of importation/assembly and are illegal with any of the above features.
Question- does the 89 ban apply to shotguns? I don't think so! so maybe you don't really have to do a parts conversion on the shotguns after all.