My QB79
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My QB79
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Topic: My QB79 (Read 852 times))
Mr. Panther
Expert
Posts: 1878
Life is good if you're the hunter and not the bait
Real Name: Cole
My QB79
«
on:
July 22, 2016, 08:22:30 PM »
I refilled my CO2 bottle today for the 79. First shot sounded a little weak, as did the next 5 shots. I could actually see the pellet coming out of the barrel LOL. I don't know what happened from the time I shot it last till now, but I imagine I will have to take it apart and see what is plugged/ jammed/ broken to cause it to lose so much velocity on a full fill. my 2 78's run good on just the cartridges so I know some thing has to be the culprit.
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vigilandy
Expert
Posts: 1967
yes
Real Name: Andy
Re: My QB79
«
Reply #1 on:
July 22, 2016, 10:05:10 PM »
You sure the tank is filled?
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Central Valley, CA
Ribbonstone
GTA Senior Contributor
Posts: 12030
Re: My QB79
«
Reply #2 on:
July 22, 2016, 10:40:04 PM »
Think you're going to come to the conclusion that the co2 leaked out in storage. Also think the O-rings sealing the tank block to the tube are the most likely suspect.
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Louisiana
7624452
Vintage Classic, currently out of production *********
GTA Senior Contributor
Posts: 19161
USA, DOD, 100% DAV Retired
Real Name: Tom
Re: My QB79
«
Reply #3 on:
July 23, 2016, 12:01:47 AM »
I have on/off valves on my CO2 tanks that solved the problem for me.
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Stranded in California
Mr. Panther
Expert
Posts: 1878
Life is good if you're the hunter and not the bait
Real Name: Cole
Re: My QB79
«
Reply #4 on:
July 23, 2016, 10:43:43 AM »
Vigil...the bottle is full. I just had it filled. the gun is not pushing the pellet very fast. It shot fine on the first bottle... ribbon, the tank was filled and full 10 minutes before I got home with it, and still has liquid in it. the problem is the velocity has fallen off so bad. Like I said it is obstructed some where as it is not getting enough CO2 to push it faster.
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Ribbonstone
GTA Senior Contributor
Posts: 12030
Re: My QB79
«
Reply #5 on:
July 23, 2016, 11:37:37 AM »
OK...will go though a long process.
This is what I hope it is ('case it's the simplest):
If you are sure it has CO2, be sure the tank is fully screwwed onto the rifle. There is a pin valve on the paintball tank. Screwing the tank on depresses that little pin valve and lets co2 into the rifle. Could be that the pin valve isn't being depressed far enough for that pin valve to always be open.
HAve had tanks with pin valves that were slightly bent do the above. Open just enough to inject some co2, which pressureizes the system and feels like the tank is solidly screwed down. Squirts in just enough co2 for a few shots.
We'll avoid static leaking (leaks just sitting around).
LEAKS AT FIRING:
Check of leaks when firing. You'll usually notice the rifle seems louder than it should be if the co2 is leaking AT THE SHOT. Are 4 seals all pretty close to eachother at the breech end.
Are two barrel o-rings, one on each side of the barrel transfer port (the hole where the gas passes into the barrel). USUALLY these can't leak enough to really make the rifle way-way slow. IF the front barrel 0-ring leaks, will get a little burst of co2 forward (parallel to the barrel). If the rear one leaks, will get a little puff back towards the shooter.
There is a bolt probe o-ring. That one can leak enough to drop velocity a good bit, but it also tends to blow gas back into the shooter's face and is usually easy to detect.
There is a transfer port seal between the barrel and the air tube. Those can leak as well, shooting gas out to the sides.
Normal test for this would be to take off the scope, fold a piece of news prring ove the breech area, and shoot a pellet. Will see the paper jump if there is a leak (and if there is a bad leak, will shread the thin newspaper).
Depending on how hard it jumped, can decide if you want to put your fingers at the possible leaks or not, but genrrally you can feel the sourse of the leak. OR you can get the area as dry/oil free as possible, dust it with flour, and the see where the flour was blown off.
MECHANICAL ISSUES: Going to have tto take it down to hunt this stuff down.
The transfer port seal can get mashed out of shape, which closes up the seal's passageway, and strangles off the flow of co2. That's not likely to happen during shooting, but it could deform into some odd strangled shape or get clogged by some stray bit.
Internally, the gas is released by the striker hitting the end of the valve stem. So if the striker became slower/weaker, would hit the valve stem less hard, and release less gas. Same is true if the gas is at higher than expected pressure (with co2, that ould be if it was left out in the heat). If the gas pressure becomes higher than it was originally, could have more pressure than the striker's hit can open fully.
Striker spring could be kinked/broken/weak. Not real likely, it would be really rare as those springs don't seem prone to weakening much and they are supported by a central guide.
Could be somthing draggin on the striker, slowing the striker down. Trigger design is not prone to sear drag, and generally if the operate at all, they'll release the striker clean.
Have had QB's that were a little warped or had too long striker pins that would provide friction if the action screws were really tightened down "bust a gut" tight. Backing off the rear acrew (which also holds the rear of the trigger assembly on) let them shoot to normal speeds. Leaving that lose isn't a great option, but it gives a clue to what needs fixing.
The only good news here is that somthing rubbing on the striker is likely to leave marks as a clue.
Have had a .177 pellet manage to drop down the space just between the bolt and barrel shank. If it does that, will fall into the bottom tube and get caught in the space between the striker and the valve stem....where it wil get mashed by the striker. That will casue slow irregular shots as the striker can't move forard it's normal amount to get to the valve stem. HAven't tried to make a .22 pellet do it; there is likely not enough room for the larger caliber.
Are ways for the valve to screw up and result in low powered shots, but will save that for later.
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Louisiana
Mr. Panther
Expert
Posts: 1878
Life is good if you're the hunter and not the bait
Real Name: Cole
Re: My QB79
«
Reply #6 on:
July 23, 2016, 05:07:08 PM »
Thank you Ribbonstone. It was my snafu, as you stated it was a problem with not being screwed down tight enough. It seemed to be till I rechecked it per your posting. It is shooting like it did before now . Once again thank you for your valued input on this.
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Ribbonstone
GTA Senior Contributor
Posts: 12030
Re: My QB79
«
Reply #7 on:
July 23, 2016, 06:30:15 PM »
Have had that happen. Figure you are screwing the tank on slowly with about 15 pounds of rearward pressure....co2 tank's pin valve opens a little...injects +900psi of co2....which pushes back with 380 pounds of force...which feels like it's bottomed out, but might be enough to pull all the slack out of the system and allow the pin valve to go back to "off".
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Louisiana
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My QB79