Canadian Airgun Forum

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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Iacio ergo sum

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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Good, Cheap, Fast; pick two.

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

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Iacio ergo sum

To close the loop on this one, with the TP hole drilled out and the hammer spring cut 2 coils:
CPHP pellets. .22 averaged only 430 fps, JSB Exact RS at 460 fps. running CO2 in the basement roughly 68F.
I replaced the hammer spring with a full length one from another QB:
CPHP ran 520 fps, and JSB Exact RS 540 fps.
So, I replaced the cut hammer spring and shimmed the equivalent of one coil.
CPHP ran at 495 fps! Voila, perfect.

Here is my garage range:

Next I sighted in using my garage range and did some pellet testing. CPHP shot terrible groups and my turret was maxed out for elevation, so back to the workbench. I shimmed the rear scope rings, eyeballed how much I would need then centered the turret (roughly, damned thing turned over 220 clicks full scale). Switched over to HPA tethered, and sent 5 JSB Exact RS downrange at 10 yards. Got AMAZING results: I was in awe..not only at how close my best guess was - actually pure fluke because I hadn't sighted in yet.



More testing showed it also likes RWS Superdomes, which I have a lot of so I zeroed the scope with those. Here is my last 5 shot group with the Superdomes.


I'm super happy with that! Especially since this was my first real shooting session in about 2 years.

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Iacio ergo sum

Yep ~ really a nice job and happy ending ~ cheers ~

P.S., why you need a camping nylon cover put on your garage ground?

Sent from my LG cellphone

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~Plinkers~
FX-M3-22 Compact#PP700-Carbine#Diana48-177#XS28M-25@26fpe#HW45 Beast#AW-Custom Z-Killer DE
~Competitors~
FWB300SU#Tau-7#IZH-46M#FWB-65#CP88-C
~Target~
HW 30s/35e/97k/40+Extender/P3+Scope/70#CZ200s Laminated@10fpe#AA ProSport-177@12fpe

Keeps the floor clean in winter; cars bring in lots of mud and salt. I back my car out for shooting, wife's car is small enough not to obstruct range

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Iacio ergo sum

Good work! Hopefully you gained some efficiency as well and a few more shots per co2 cartridge.

Sent from my EML-L09 using Tapatalk

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Website: https://airgunarcheryfun.ca/