I have a Crosman 150 that has been rebuilt.(I didn't rebuild it) it has an odd quirk. Put in a new CO2 cartridg(e and the gun works fine. Leave it sit over night and it may fire or it may not. If it doesn't it just sounds like it has no CO2 in it and when you cock it it just makes a thud sound. Now here is the kicker the gun still has gas in it under pressure. I have no idea why it is acting like this. Any ideas?