I'm confused.....
Can't any gun with a mag accept a mag that holds ten or more rounds even if it wasn't originally designed to do so?
The 1911 is designed to hold 7-8, but you can get 10+ round mags.
Yes, any gun with a DETACHABLE magazine can be fitted with a magazine that holds more rounds. The antis don't want you to have any guns anyway and would prefer you only have one shot if they have to allow you to have a gun at all so they don't see any contradiction.