I have an 1100 and I have an extra barrel I would like to cut down to 18". I read somewhere that reducing a barrel length may alter the function because of the ports.
Would appreciate some advice.
My advice is to try to trade your barrel for a 20 inch cylinder bore one. Any factory barrel, once cut down, has changed from an accessory of varying value to a modified part of quite a lot lesser value. Cutting any shotgun barrel is a dicey business these days, with most smiths avoiding doing it, and always to 18 1/4" to be decidedly on the right side of the law. A factory 20 inch cylinder bore barrel, so marked, is infinitely superior to any cut down 18 incher IMO.
While 4575 is correct, I cut down a barrel to 12” and had to open the ports to get it to run 100% with my skeet loads…I don’t remember the size I had to go to but it wasn’t much. If I had to guess you won’t have to open up the ports at 18”…you need to stay over the 26” rule, so measure that distance BEFORE you cut the barrel, as you can get in some trouble.
I am sure to about 9 decimal places that 18 inches is the minimum barrel length for a shotgun, and 26 inches is the minimum overall length for the gun. BATF has these measurements set in stone unless I am wrong, and any shotgun that does not comply with both of them, except a registered NFA exception, such as an original Marble's Gamegetter, is contraband.