QB78 CO2 trouble getting pierced .

[N6CRV]

Hello, I might be having trouble in that if I put two new co2 cartages in. It seems like only one is getting pierced at a time. I put two new ones in and tighten the cap all the way down. Then I back it off about 1/8 turn and it will not go farther, as it stops. That is fine as I can then shoot with full power for around 25-30 shots. Then the rifle will get weak like out of gas. But then after trying to empty the rifle to be able to but new cartages in, I get full power again for another 20 or so shots. Like I was to put in a new cartage. If I just put one cartage in, with the new one (tip pointing at the cap) works fine. I just tighten, then back off 1/8 turn and cap will stop. If I put the one new cartage in first and tighten it down, it will take 5 to 8 shots before I get CO2. It will then shoot fine for around 20 shots. Looking at the cartages the holes in the end are VERY SMALL!! I don't have a drill bit or Allen key that is that small. A .050 Allen key is way to large. But it will fit into a hold that my 2240 makes. What is causing this trouble or is this normal? Thanks for the help!!

[vigilandy]

Haven't tried it myself, but I've heard some guys putting a coin between the cartridges to increase pressure on the piercing pins...

[N6CRV]

Haven't tried it myself, but I've heard some guys putting a coin between the cartridges to increase pressure on the piercing pins...

Going to go and give it a try.

[N6CRV]

Ok, no change at all. I put two dimes in-between the cartages and it took 6 shots before I got any gas. So does not seem to help. The only mods that I have done was to take the cotton out of the valve. Other then that stock.

[QVTom]

It is normal for piercing to take place in two steps.  Generally the cart nearest the muzzle is pierced when the cap is screwed on so it is important to screw the cap all the way without stopping.  No need to back it off or over tighten. The cart that faces the valve is pierced when the gun is cocked and fired.  I notice with my Crosman 160 (qb is a direct copy) I need to do 2-3 dry fires before there is consistent pressure.

If you think both your carts aren't piercing I'd try to determine which one is not getting poked.  A weak hammer strike could be responsible for the rear cart not to get pierced and a too short pin on the cap could keep the front cart from piercing.

You don't need much of a hole for the gas to escape and fill the tube.

Tom

[N6CRV]

Thanks Tom, you make it sound like mine is normal. When I tried it with the Dimes I did not back it off and it did cut down the times that it took to pierce it. I read that you are suppose to back off the cap a 1/8 turn that is why I have been doing that way. If the cap is not backed off how does the gas it out? Now that it has warmed up I have been having more fun with the QB and saving my pump arm for cold weather.
 

[QVTom]

Backing off an 1/8 is fine.  Most will back off just not to bottom out the threads but really serves no purpose.  The gas molecules are small, they will just slip past the piercing pin.

Tom

[chuckinohio]

  The piercing pin in the valve may be hanging up on the front orifice of the valve.

  When you removed the felt and screen from the valve, did you remove the washer, or leave it in? That washer acts like a sort of guide for the piercing pin, keeping it somewhat centered in the valve.

  You could try polishing the nose of the piercing pin so that it glides a bit smoother. it may be hanging up on the valve body.

[stevemag]

  The piercing pin in the valve may be hanging up on the front orifice of the valve.

  When you removed the felt and screen from the valve, did you remove the washer, or leave it in? That washer acts like a sort of guide for the piercing pin, keeping it somewhat centered in the valve.

  You could try polishing the nose of the piercing pin so that it glides a bit smoother. it may be hanging up on the valve body.

I agree, if a dime won't fix it I think you can rule out a batch of short co2 cartridges .(happened to me).  Time to open her up and look at the valve, it's a PIA at first but you get the hang of it after a few times.
Also, depending where and when you got it. There were some guns that had a tube a mm or 2 too long and some that needed a different cap. But if you've been using it for a while and it's worked, I'd bet on the valve.

[N6CRV]

When I took the Valve apart I only took out the felt, left the washer. I have been shooting it and it has been fine. I did put a cartage in facing the cap tonight. I tighten the cap down and did not back it off. It worked just fine other then the cap getting very cold. I would not of even thought there was any thing wrong as it shoots great and hits when you point it. But I am getting that second charge of CO2. Guess it is just a little extra for free. I think what got me looking at the hole was I has some used 2240 cartages laying around. What a big difference in the hole it makes in the cartage. From what I have read about 35 to 40 is about right for good power shots and I'm getting that. Thanks for the replies!! Oh I didn't think it comes apart that bad. I did clean all the edges when I had it apart.

[Josan]

The felt has two functions:

• help centering the piercing pin
• help avoid the gun spitting out liquid CO2

At 1. I have noticed that taking out the felt will lead to the piercing pin catching at the rim of the valve hole that goes to the cartridge.
At 2. The valve should release gaseous CO2, not liquid CO2. So the felt helps prevent the free flow of liquid CO2 from the tube into the valve and promotes the evaporation of liquid into gas. You don't want your QB to spit out liquid CO2 after you have held it straight up for a short time. This leads to extra CO2 consumption, more noise and shot-to-shot inconsistency.

[N6CRV]

Thanks for the info. I still have the felt I think I will try putting it back in and see.

[N6CRV]

Well I put the felt back in. It pierced the cartridge on the first shot.
Thanks.
 

[Josan]

We're all here to help each other brother.