okay, so i broke out an lb bolt and threw it in tacolex's k2, here's a pic of the 'stop' i was talking about...
if that ring went into the barrel as it looks to have, it'll take some force (dowel down the barrel?) to remove it...did the bolt still have the locking bb's? the locking mechanism is all the way forward as well...the location of the bolt in the pic above is how far back it'll travel before the cocking jug hits the back of the slot...