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PostPosted: Thu Nov 01, 2018 7:13 pm 
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Joined: Fri Jan 22, 2010 1:17 pm
Posts: 1566
Location: Kingston
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I am slowly getting back into shooting and tuning, and have turned my sights onto my Beeman QB78. My intention is to re-barrel it to .22 and tune it to stay non-PAL. I have done this type of tune on many QB/AR7xx in the past so achieving that shouldn't be a problem. However, what is interesting me now is trimming the hammer spring to save CO2. I read here recently quite a few threads suggesting a lighter hammer spring would not reduce fps by lots, but would save lots of CO2. I could/would trim the spring first and tune after...but my question for now is: how much should I cut off the hammer spring bearing in mind I'm staying with non-PAL and .22?

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PostPosted: Thu Nov 01, 2018 8:57 pm 
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Joined: Thu May 04, 2017 6:41 pm
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Location: Vancouver BC
My non-pal hammer spring is cut down to 56mm long. That and two washers get me 495fps on CO2 at 70degF with 18.1gr .22cal pellets
My valve is moded some; rear peircer removed, valve spring sits on a notched washer for air flow, enlarger valve output and transferport, 1/4 tubing TP,

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PostPosted: Fri Nov 02, 2018 8:50 pm 
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Joined: Fri Jan 22, 2010 1:17 pm
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Location: Kingston
Thanks, I cut a coil of the hammer spring and did a tune. The TP hole in the valve was only 1.5mm diameter, so I drilled it out to 3mm. I was going to go 4.3mm (0.17") but decided to take it slow and in steps. Filled with one 12g cartridge no leaks. Here it is with a Browning 3-9x40 AO. BTW, fit and finish in this Beeman QB78 was way better than I have seen in earlier Industry Brand QBs. The seals were in excellent condition, and even the TP seal was clean and true. I reused it instead of replacing with tubing. Curiously, not a single fastener was any more than finger tight, some weren't even that much! I'll chrony tomorrow and try to find pellets it likes :D :) 8)


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