qb78 tuning advice needed
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qb78 tuning advice needed
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Topic: qb78 tuning advice needed (Read 1262 times))
farmerJohninVA
Shooter
Posts: 37
yes
Real Name: John Varga
qb78 tuning advice needed
«
on:
October 01, 2015, 11:52:47 PM »
Hello all.
I purchased a 78 after much lurking and reading posts about the endless tinkering possibilities. I am amazed at the wealth of knowledge here. My eventual plan is to get it to hpa.
my progress thus far consists of opening up the tp, bolt, valve, brass screw recrown, trigger lightening, and general smoothing.
It really seems to hit harder after tuning.
I get a nice cloud of vapor when I fire it, so I am thinking I am wasting co2.
My options appear to be either clip the spring, lighten the hammer, or bstaley mod. Still not 100% sure how that happens, an o ring acts like a buffer and keeps the hammer from getting a full stroke strike?
Don't have a chrony so am doing this based on yalls experience.
thanks
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Prince George Virginia
nervoustrigger
GTA Senior Contributor
Posts: 8701
The Grin Reaper
Real Name: Jason
Re: qb78 tuning advice needed
«
Reply #1 on:
October 02, 2015, 01:05:15 AM »
In the simplest terms, the O-ring stack limits the valve travel, preventing the hammer from overdriving it, so to speak.
The stock hammer strike is definitely too much for CO2 pressures at modest temperatures. Certainly is once you open up the horribly restrictive valve, transfer port, and bolt probe. I'm more familiar with HPA conversions but there's no doubt in my mind that you'd be able to wring out the longest shot string with a bstaley mod. Just be prepared for lots of experimentation. It helps to be able to adjust the hammer strike when tuning a bstaley buffer so my advice would be to start with an RVA and see where that gets you. Adjust it until you find your maximum velocity for reference. Then if you want to tinker with an O-ring stack to squeeze out a higher shot count, go for it. Keep in mind that the O-ring buffer has the best potential when downtuning slightly.
But step 1 before any of this is buy a chronograph. Anything else is just guesswork.
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MS
Conduct yourself so that when a man accuses you of something dishonorable, no one will believe him.
Barrel accurizing guide
My youtube channel
QB79 HPA conversion
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farmerJohninVA
Shooter
Posts: 37
yes
Real Name: John Varga
Re: qb78 tuning advice needed
«
Reply #2 on:
October 02, 2015, 02:33:18 PM »
Thanks for the comments, unfortunately I cannot justify much more than lunch money on this project right now so I will just make generalized assumptions for the time being.
that being said, I will find some o rings and experiment.
I see I had a brain fart and posted on the wrong gate, but still worked.
Thanks
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Prince George Virginia
nervoustrigger
GTA Senior Contributor
Posts: 8701
The Grin Reaper
Real Name: Jason
Re: qb78 tuning advice needed
«
Reply #3 on:
October 02, 2015, 04:17:15 PM »
Perhaps I'm misunderstanding your concern about cost but an RVA is essentially free. All you need is a machine screw; a 10-32 x 1.5" works great in my experience.
Okay, maybe a few bucks if you have to buy a tap.
[Edit]Sorry, just realized you were referring to getting a chronograph [/edit]
«
Last Edit: October 02, 2015, 04:23:32 PM by nervoustrigger
»
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MS
Conduct yourself so that when a man accuses you of something dishonorable, no one will believe him.
Barrel accurizing guide
My youtube channel
QB79 HPA conversion
2240 HPA conversion
Intro to PCP airguns
farmerJohninVA
Shooter
Posts: 37
yes
Real Name: John Varga
Re: qb78 tuning advice needed
«
Reply #4 on:
October 02, 2015, 04:56:56 PM »
Correct about the chrony, just dropped a chunk of change on a front end rebuild on my truck, plus 4 new tires, andddddddd my daughters spring tuition will be coming up soon. Orings and some machine screws might make it.
I've set timing by ear, sometimes close enough is good enough until you can do better.
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Prince George Virginia
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qb78 tuning advice needed