Crosman 150

[jh45gun]

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?

[georgerkahn]

The 150 had a reputation as a notorious leaker. My memory recalls it's first introduction in the early to mid-1950s, continuing through the mid 1960s with at least two, maybe three versions. The very early ones both had a rubber seal with a remarkably short life, and were powered with the very first ~12 gram CO2 cartridges having pre-weld soda/beer crimped caps on top, almost guaranteeing gas pressure not sufficient to do more than a "thud" the next day. The later versions were made to accept the new, smooth-top CO2 12 gram cartridges.
A "trick" folks I knew used to do was to take a drop of Automatic Transmission Sealant and put it atop the CO2 cartridge before insertion. If this doesn't solve your problem, I'd replace the barrel seal.
I have no idea if this might help your pistol... but, it may be worth a try. Good luck!
geo

[jh45gun]

It holds gas and isn't leaking out. That isn't the problem.

[Jonah]

Are you sure it still has gas in the tube? If the o-ring in the cap has absorbed CO2, even though the gun no longer has CO2 available to shoot, the cap o-ring may be so swollen that you can't unscrew the cap. Wait a few days and see if it will unscrew. Don't use pliers on the cap and ruin it with ugly marks. A strap wrench will get it open but that will probably ruin the o-ring, which is ruined anyway if it absorbed the CO2. Maybe this helped.

[jh45gun]

Only way to take out cart is unscrew cap slowly. I use a leather on the jaws of a small vice grip unlocked. I am going to send it to a friend to see if he can figure it out. I am positive it has gas left in the tube! That's what I stated several times.You can hear the gas hiss out after cap is loosened.

[Multigunner]

Sounds like the striker isn't hitting hard enough to open the valve.
My SSP 250 has a similar striker and when left too long in the sun the pressure of the gas is too high for the valve to open.
In your situation I expect that when first charged the gas is cool, and when fired the release of gas cools it further, when left for any length of time without firing the temperature rises just enough that that gas pressure increases slightly and a weak striker fall won't open the valve.
A caved in seal on the exhaust valve will make such a situation worse. One of my older 760 rifles with brass exhaust valve and separate seal stopped firing and tearing it down I found the seal was indented so far that the seal never fully cleared the valve seat when fired. A new one piece exhaust valve solved that quickly.