GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => China/Asian AirGun Gate => Topic started by: RMM on May 15, 2014, 05:31:22 PM
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Well I got all my leaks fixed, checked and rechecked everything on my Bobcat to where I could sling some lead over the chrony so here's where I'm at and open for any tuning ideas as I'm a novice but willing to learn, so with that said I start.
This repeater is sweet and I think I'm at the point where everything is equal to rsterne's 60 tune http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=59114.0) except for stalwart's bolt, internal chamber o-ring, Teflon coated striker and my valve and striker tunnel is steel lined. Yes I said steel lined another specialty of stalwart's I'd requested after noticing the stock striker damage to the aluminum tunnel.
Another thing different is my mainspring and valve spring lube of choice, http://www2.dupont.com/Consumer_Lubricants/en_US/products/multi_use_lubricant.html (http://www2.dupont.com/Consumer_Lubricants/en_US/products/multi_use_lubricant.html)
This is the valve I'm using with .500 spring height (I believe is the same as from the factory) for the valve stem pressure. http://www.gatewaytoairguns.org/GTA/index.php?topic=65877.msg637252#msg637252 (http://www.gatewaytoairguns.org/GTA/index.php?topic=65877.msg637252#msg637252)
Bstaley mod instated using 3 - 70d, and I have 90d on hand.
Here's some numbers.
adjuster fully screwed in towards front of receiver, 1.5K psi starting point, CPHP 14.3gr:
942.60
933.88
906.94
863.10
824.47
808.02
776.30
739.82
adjuster fully screwed out towards rear of receiver, 1.5K psi starting point, CPHP 14.3gr :
912.27
921.65
919.20
920.95
917.60
908.23
901.74
873.81
862.30
843.96
835.40
821.90
806.89
809.80
782.27
error
What might be some ideas to get to a bell curve with 16 usable shots as I think there's something different in my build than rsterne's build because I'm out of adjuster and turning the adjuster in makes things worse. Before cutting coils, or do something wrong, I beseech the collective wisdom of GTA.
Observations on my part:
1.) There's approximately .100" before the striker shoulder (not speaking of the nose) hits the 3rd bstaley o-ring. i.e. There's room to shim.
2.) I can increase my valve spring pressure with it's Delrin retaining nut
3.) I have found no impingements causing the valve to stay open longer than it should.
4.) There is already very little preload on the mainspring with the adjuster turned full towards the rear of the receiver.
5.) I'm thinking the Teflon striker and steel liner are making a big difference in this build with possibly the stalwart bolt and chamber internal o-ring fitting into the equation also.
6.) Trigger group all the way to the rear
7.) Barrel port .169"
8.) Valve stem protrusion .131" past striker block
9.) Valve throat .201" and exhaust port .191"
Thanks in advance folks
edited 5/16/14 to add 6.) through 9.)
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Restrict transfer port.
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Slide the trigger group forward in 1/32" increments. It'll slightly reduce striker travel and should extend the string, albeit at a lower velocity.
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Looks to me like your bstaley buffer isn't engaging and needs shimming....
Bob
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Looks to me like your bstaley buffer isn't engaging and needs shimming....
Bob
I couldn't find this info on the bstaley when I searched.
Question: Is the correct set-up to have the striker touching the stem at the exact same time it hits the o-ring?
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Thanks for all the viable and great suggestions gents.
I had an anomaly but tracked it down to my Delrin valve spring nut backing off decreasing valve spring height (pressure) so I fabbed up a Delrin jam nut for now. I'll look into brass or aluminum for the valve spring nut and jam nut for more coefficient in friction than the Delrin.
Anyway here's what I came up with:
a.) bstaley shimmed .046
b.) Trigger group full forward
c.) Adjuster full to rear
d.) 1.5K down to 1K
e.) CPHP 14.3
(I have some JSB 18.13 Exacts I'll run through the Bobcat tomorrow.)
733.59
741.04
746.52
744.78
739.23
741.86
error
739.73
736.85
732.12
733.10
727.06
I think I'm getting closer, what say ye?
Anymore suggestions?? e.g. More pressure 1.5K to 1.6K or further?
Will it be better to keep my shot count to 8 good shots and not get tied up with 16 good shots??? More FPE for groundhog type pests?
Thanks