Nope, no threaded end cap. Double checked and even dug out the manual. Parts diagram clearly shows a one piece tube, threaded only in the receiver (not ready to try and take that out yet). The muzzle end of the tube has a plunger type arrangement inside and the ends of the tube are crimped in to keep it in place.
Chriss, I appreciate your help though. Do you have an M3? I am wondering if the model changed over the years. Mine is a post-ban, maybe '98 manufacture.
Thanks.