QB79 .22 caliber accuracy?



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Offline PaperPunch1

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QB79 .22 caliber accuracy?
« on: November 02, 2017, 10:49:57 PM »
Does the b79 shoot better at certain velocities? Mine is switched to HPA but will (at 25yds) shoot three or four inside a penny then all of a sudden throw the next two or five all over.....then plant two more in the same hole before spraying three more, then plant one on the crosshairs or maybe two, then way off again. Is this normal for the qb79? I tried JSB exacts, FT Trophy, and several others, but it seems to shoot the CP domes as good or better than any I tested. I am shooting around 850psi from a ninja regulator, and am thinking about adding shims to increase pressure, hoping to get better groups. Maybe its just the barrels are cheap?
Any ideas?
Thx in advance for guidance if any!
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Offline nervoustrigger

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Re: QB79 .22 caliber accuracy?
« Reply #1 on: November 03, 2017, 12:27:31 AM »
I haven't seen that degree of inaccuracy resulting from velocity.  A few of the QB HPA conversions I've done, I've dialed them way back and still gotten good groups.  One example that I documented here was a 30fpe tune that I dialed back to 15fpe for a discreet suburban squirrel removal visit to a friend's house.  It went 6 for 6 that morning.
http://www.gatewaytoairguns.org/GTA/index.php?topic=78577

The barrels are indeed cheap but usually quite good once cleaned up, better on average than most other cheap barrels I've dealt with.  Actually every one that I've worked over has printed sub-MoA 5-shot groups at 25 yards and often at 43 yards.

My guess is there's a burr left behind from machining the barrel that's damaging your pellets.  And actually the fact you're getting better results with Crosman pellets is another indication.  I've seen the same thing with QB barrels right out of the box.  My theory is the harder alloy is less prone to being damaged.  But once the burrs are removed, they always do better with a JSB or Air Arms pellet.

My full barrel regimen is described here if you're interested:
https://www.gatewaytoairguns.org/GTA/index.php?topic=130555

Offline 1953 Panther

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Re: QB79 .22 caliber accuracy?
« Reply #2 on: November 03, 2017, 06:05:54 AM »
I had that problem with a .177 QB79 i bought last month. It turned out it was my scope, and me both, that was causing the problem. I put a Williams peep sight on it and it got tight groups with no fliers after that. Most are more proficient with a scope than I am, so it might just be a cleaning the barrel issue, or as Jason mentioned it could be burrs in the barrel. Try grouping with the open sights and see if that makes a difference. if it groups well with no fliers then it could be a scope issue.
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Offline PaperPunch1

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Re: QB79 .22 caliber accuracy?
« Reply #3 on: November 13, 2017, 09:29:02 PM »
Accuracy got much better at a higher velocity. I managed 838fps average with 14.3grain CP domes. Using 1000psi now to launch them down range....(HPA)
Anyway, the 1:18 barrel twist seems to like that combination!
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Offline Neil54

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Re: QB79 .22 caliber accuracy?
« Reply #4 on: January 05, 2018, 01:19:06 PM »
If you carefully push a pellet down the barrel, check for damage to the skirt when the pellet pops out, could be a burr either at the crown or transfer port hole.

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Offline Neil54

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Re: QB79 .22 caliber accuracy?
« Reply #5 on: January 05, 2018, 01:24:54 PM »
Should have said you can check for burrs with a Q tip.
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Offline BrushPopper

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Re: QB79 .22 caliber accuracy?
« Reply #6 on: January 06, 2018, 05:20:48 PM »
Most of the time, a problem like yours is a rough/burred bore. I've turned such cases into shooters by polishing the crown (sharpened pencil/cordless drill and lapping compound, and by fire-lapping to polish the entire bore.

Good luck!
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