I have read about this a few times - here's a thread from another forum on the exact same issue, same gun, same cartridge .... seems to be common ....
Looks like there are some "longer" aftermarket magazines that allow a longer COAL.
One thing I picked up from this - you are still limited to 3.56" but that's still a bit better than the 3.4" you are limited to now anyways ....
Good luck ...
http://www.rokslide.com/forums/firea...ngth-coal.html