Replaced the airsoft gun in my Pershing. The original was jamming. Appears to be no damage to the original gun. New gun is jamming - the bb's just don't travel up the barrel.

Question: is it possible that the aluminum barrel liner has moved forward? How do I seat it into the airsoft gun? Or, if this is not the problem - any ideas on a fix? I have tried better bb's but this does not help.