Where can I buy a QB power adjuster?

Where can I buy a QB power adjuster?

Joined: April 12th, 2006, 7:56 am

December 13th, 2017, 2:22 am #1

I've got a QB-79 HPA that I'm setting up as my back up gun for Hunter FT. It shoots its favorite pellet(JSB 8.4) at 860-870fps. I'd like to push them out to 930fps. TIA!
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Joined: June 4th, 2013, 4:42 am

December 14th, 2017, 3:24 pm #2

I haven't searched exhaustively but I am not aware of a completely off-the-shelf power adjuster for the QB. If that's the case, it's rather shocking given the popularity and longevity of the QB platform. The closest thing I could find was this thread where the author made a slight modification to a Crosman power adjuster to make it work: https://www.gatewaytoairguns.org/GTA/in ... opic=99574

I just modify the existing one with a #10-32 screw that is offset to miss the long bolt that secures the back of the trigger assembly:



In this picture, I have close-fitting center punch through it so you can see that the screw clears it.


You might think the offset screw would contribute to velocity inconsistencies from shot to shot but because it simply locates the back of the spring guide, it works great.

Be aware that you need to remove the rear cocking pin for this mod to work. Doing so changes it to cock-on-open which I think is advantageous because it allows you to discern a poor fitting pellet when closing the bolt and it extends the life of the bolt O-ring.

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Joined: June 4th, 2013, 4:42 am

December 14th, 2017, 3:33 pm #3

I've got a QB-79 HPA that I'm setting up as my back up gun for Hunter FT. It shoots its favorite pellet(JSB 8.4) at 860-870fps. I'd like to push them out to 930fps. TIA!
By the way, the spring tension in factory form seems to be about right to obtain peak velocity from HPA of about 1100-1200psi. If you are not running a setpoint of 1300-1400psi, you may not see any increase from adding preload to the hammer spring. Pressures much higher than that get kinda sketchy in terms of blowing a 1.8k burst disk, particularly if the rifle is taken from a cold setting to a hot setting because it causes a pressure rise in the plenum.

For your safety, do not use a 3k burst disk because consensus is the QB, being designed for CO2, is not safe if the valve seat fails and exposes the air tube to the full pressure of a 3000psi fill. The tank block in particular is the concern, given the proximity of the screws to the end of the tube and the fact there are flats milled into the tube which reduce its thickness. It would be prudent to read up on pinning the tank block for better safety margin.
https://www.gatewaytoairguns.org/GTA/in ... pic=105712

It's easy to do. Example:

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