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All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Before and After on my QB Tune

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Fisherdude:
This past January, I purchased a QB78 from ^&$@_=s.  I haven't been satasfied with the accuracy, so I went to work on it.  
* Replaced .177 barrel with a .22 barrel
* Re-cut and polish crown
* Opened up gas passages for more CO2 to increase velocity per instructions on CDT web site
* Pinned the end of the bolt (Facrory bolt pushes on the skirt to seat pellet - I didn't like that plan)
* Polished the loading ramp
* Put in a second set screw to help hold the barrel
* Replaced the o-rings on the bolt and barrel
* Polished the hammer
* 3 washers behind the hammer spring
* I did not remove or modify the valve

Before I did all this, I was getting pretty crappy groups - about 2 inches at 20 yards. The rifle was shooting at 500 fps with .22 CPHPs and JSB Exacts.  After the tune, it is shooting 690 -700 fps with the same pellets.  Plus the accuracy is now to my liking.  Now I have enough fpe for hunting and the accuracy to comfortably take a squirrell at 30 -40 yards.  The most interesting thing to me was that the accuracy with the CPHPs improved so much.  

snookman:
 That is a drastic improvement.

 It just shows how a few modifications can turn a so so gun into a KEEPER.

 Great job, snookman

dk1677:
Nice job!

Bentong:
That's outstanding job on getting her shoot with tight grouping. On my QB79, I had to go from .22 to .177 and very satisfied it shoots different pellets tightly.

MichaelM:
nice job!! now to mod the valve for a touch more flow and add a hammer debouncer and your golden!!!

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