In experimenting with my 11-48, I have gone as far as a 5 shot mag extension tube with the barrel cut back to 22". Since you can't use a barel clamp, the 5 shot mag extension gets kinda whippy and I was worried about snapping the threaded end off the mag tube. So I decided to not go past a 3 shot extension. No problems after about 1000 rounds, except extension tends to shoot loose after 25-30 rounds, so I just reach up and tighten it 1-2 clicks every so often.