AutoOrd. Thompson Model 1927, semi auto, pistol currently has 10" barrel. Owner curious if he can cut back the barrel and put brake on end. Brake is not an issue and I felt that since it is legally classified as a pistol, should not be any limit on barrel length. The firearm is currently 23" long, but again, did not think a pistol has any limitations as to overall length.
All input on this would be appreciated.

He can shorten it all he wants. He can NEVER attach a buttstock or a foregrip to the pistol is the restriction on pistols.

Thanks for the feedback. As you mentioned, I told him about the buttstock and vertical foregrip items, but did not think the barrel length was an issue. I also have the same pistol(have a hard time thinking of this firearm as a pistol even though it is sold as such) and it has it's good and bad points. Should have known, but if you hold the pistol loosely, things happen. It will jam due to lack of resistance to the recoil and the bolt(heavy block of steel/springs/etc.) will not pick up the next round. The trigger has a very long pull with very light let off at final stage and it will "bump" fire due to recoil and trigger pull. By placing end of pistol against chest or shoulder area and pulling back firmly, it runs very well with no failures to feed or doubling. With hardball ammo, accuracy from bag is a lot better than I would have predicted and 50yd groups are quite good. Also found that you need to run the gun wet for better performance. Mine is short enough and now that I have worked with it for a while will leave it as it is.