Also, make sure that the bolt-plug is turned out about one and a half turn. One of the causes of bolt-stick is having your plug screwed in all the way. However, most of the time it's caused by an over-pressurized HPR.
While the bolt is stuck forward, try decreasing the pressure on the HPR about 1/4 turn, then let the marker sit for a couple of minutes so that the regulator stabilizes while you increase/decrease the LPR pressure
If it doesn't work, then try decreasing by about 1/4 turn while you continue to adjust the LPR, etc