problem loading co2 in qb78

[poomwah]

Well, I finally had a chance to shoot again. Used up the co2 that Mike had in the gun when he sent it. I put a pair of daisy powerlets in it, cranked the knob in as far as I could and backed it out 1/4 turn. I could hear a hiss, tried tightening it up but couldn't. Fired a couple shots.  Set the rifle down to mess with the target (kept falling over), came back and the rifle was already empty.  Put a couple crosman's in it, cranked it in, backed it out a 1/4 turn, nothing. Backed it out a little more and nothing, backed it out a little more (about 1/16 of a turn each time) and would try to shoot it, nothing happened until gas started leaking at the cap and dumped all the co2.
   what am I doing wrong?

[grumpy]

You may have smashed a seal or something. I never tighten em up as far as they go.

Dave

[poomwah]

the seal looks good as far as I can tell.
the only co2 gun I've had before this was a daisy 15xt pistol.  I was expecting to turn the knob until you could hear it .  How do I know on the qb when the powerlet is punctured?

[SAADE]

poomwah:  1st cartidge goes in tip first towards breech, 2nd cart goes in butt end first with tip towards cap, did you do that?

Also, for Bulk-Fill, there are two versions of the QB78 "bleed hole", which is a very tiny hole in the top of the threads between the barrel and the co2 tube (hard to see). Older versions were drilled closer to the end of the threads in the tube, newer versions were drilled about .100" further back so, if you have newer gun with "older" cap, the o-ring in the cap misses the bleed hole by about .100", ie the o-ring is sealing ahead of that hole and thus, co2 leaks out. This is for the Bulk-Fill only, the co2 carts cap should not have been affected.

I was the first guy to bring this to Stephen Archers attention a year ago and I made a second o-ring groove on my cap to match the new bleed hole location. Click on the pic attached and also go to  http://www.@#$%^.info/search/label/QB78%20Family  for more info.

Last, my experience with the cap for co2 cartridges has been to thread all the way down (which pierces the co2 cart at the end under it) and then back off about 1 turn or more and shoot gun to puncture co2 cart #2 down inside. It's amazing how freakin tight that cap gets under pressure!

[poomwah]

just wasted another powerlet.
they are in the right direction.  the cap and tube must be right because it was working when I got it (already had two co2 powerlets in it). 
I tightened it down, backed it off a bit , nothing.  Tightened down a bit more, backed it off a little, nothing.  Tightened down a little more, backed it off about 1/8 to a 1/4 turn and it starts spitting co2 out the threads.
Maybe grumpy is right and I smashed the seal by tightening it too tight earlier.  Seems odd though, because even though I was tightening it as far as I could, I was only using my thumb and pointer finger. Is that even possible?

[mikeiniowa]

the valve may be loose as the sound is from the valve and it's not coming out the barrel?? need to tighten it with a long screwdriver or 3/4 wide by 1/8 thick strap steel tool...

[poomwah]

thanks for the emails Mike , I appreciate the advice .
What do you guys think of this picture.Does the seal look right?

 I've never seen another one in person, so I'm not sure, but from the pictures I've seen online, it looks like the outside diameter of the seal is slightly larger than the diameter of outboard side of the plug.  Mine is flush. It's also rather hard.  Although I have no experience with QB's, from my highly experienced mechanical background, I would not expect this seal to seal.

[mikeiniowa]

that o-ring is shot.....turning it under pressure has rounded it down, run the cap down until it's just snug on the cylinder,  then shake the rifle if you hear the cylinders sliding back and forth then turn it down until the clicking stops but hasn't opened the cylinder, then fire and they will both open, I can send some o-rings if you want some, no problem...

[stevemag]

i had the same problem, turned out there was a chunk missing from the o-ring seal. i replaced it with an o-ring from the hardware store but they dont seem to work.(tried a few) they swell up after 1 or 2 times.  you need to get a white one from Archer Air. ( i do too)

[SAADE]

+1  to the other comments and.. you need the White O-ring because, it has a much higher permeability rating, fancy words for doesn't soak up the co2 molecules and let them pass through and also won't swell from any oils (much).

A new one, with a little Pellgunoil and you are golden!

[SAADE]

poomwah; PS, yes, your co2 Cap is just like mine and all others, no issues there.

[farrlarr]

You do realize that the first cartridge isn't punctured until you shoot after putting the cartridges in and screwing in the cap, don't you?  It appears to me, from reading what you have posted, that you are screwing in the cap and then backing it out until you hear gas leaking, which results from puncturing only the second cartridge with the cap itself.  Backing out the cap until you hear gas leaking tells you that the second cartridge is punctured but pressurization of the tube with the gas from the cartridge makes it really difficult to re-tighten the cap, which basically leaves a leak.  I simply tighten the cap snugly, shoot the gun twice without a pellet and then go on about my shooting.  As far as I can tell, there is no reason to tighten the cap and then back it off; listening for gas leakage as assurance that the cartridge is punctured is of no use at all.  Simply shoot the gun twice; you will easily be able to tell that the gun is charged because the second shot will be much louder than the first and I can generally see gas (?) shooting out on the second shot that was not visible on the first. 

I realize that I am mostly repeating what SAADE already said in his first post.  Hopefully, stating it a bit differently will reinforce the message.  Only real difference here is that I am not aware of any need to loosen the cap after inserting cartridges and tightening it in the first place.

[SAADE]

farrlar: Good follow-up info and... I should have noted that my rifle is the AR2078 which has the de-gassing port and tool which allows me to relive all pressure which makes the cap come off easily regardless.

[poomwah]

Thanks everybody, I understand what you are all saying, I was just following the instructions. I wasn't turning it out in order to hear gas (I had initially expected to hear gas when I turned it in), I was turning it back out because the instructions say that if you don't back it out, that the cartridge will seal against the cap and not allow gas into the tube.  The reason I backed it out far enough to allow gas to escape was because it wouldn't fire, I tried to fire it, and had nothing, as per the instructions, I backed it off a little, tried to fire it again, etc. And it wouldn't fire.
  Another thing that I am confused about is  that the manual says its supposed to be difficult to turn the knob when under pressure. Mine was easy to thread all the way out.  
I'm not trying to argue, I'm just trying to understand.
 Also, just so I know , are these o-rings really that delicate that you can destroy them instantly?

[SAADE]

O-rings, they can get damaged as they pass the opening/edge of the tube if it is not super smooth. You can do a litle polishing on the inside edge and down about one inch BUT, be sure to stuff a small, clean cloth in there first to avoid any metal particles from getting into the lower works. Even then, blow out the tube extremely well when done and then pull the cloth out with a needle-nose plier or a coat hangar hook, followed by another balst of air to insure all is clean.

[poomwah]

So, are the Melick guns different in their operation? I notice that the manual (and Saade) would have you pierce the cartridge, then back the cap out a little.
But Mike and Farrlar would have you tighten it and not back it off.  Obviously Mike knows these guns, I'm curious why its different.  Is there anything else thats different about them I need to know?  I don't want to mess anything up.
And I'm sorry for all the questions, but what about using one new cartridge and one empty.  The instructions say put the empty toward the breech. Then follow the normal procedures.  What is the right way to do that? Just thread it in and leave it? Thread it in until it barely touches?
Sorry again for all the questions

[mikeiniowa]

for one cylinder use put full in first then empty, then run cap down until it touches and back off an 1/8 turn (cylinder is already open so it will seal. For two just do like I said as that works good on all the 78's...done right it opens both and you don't have the stress on the o-ring from turning under pressure...

[poomwah]

Thanks for clearing that up Mike, I appreciate it. I also appreciate everything else.
Guys, if you are going to get a gun, and Flying Dragon has them, it is DEFINITELY the place to get it from.  I have NEVER even heard of customer service as good as his.

[SAADE]

Amen to that, SERVICE and with a smaile too!

[poomwah]

Got my new cap seals from Mike today. Thanks Mike !!!
Took care of the problem, I LOVE shooting this rifle.
found out that it really likes crosman destroyers too