130fps increase w/ 12" to 18" change out. How, Why
Alright, i did a shot string yesterday with my 18″ barrel in, Blodnob valve and gained 130fps over the 12″ barrel. Is it that i just maximized the air release with the barrel length? I think this confirms my thoughts on the 12″ barrel being a waste of air with Sean’s valve. Tophat adjusted the same 2.4mm, 21g Kodiaks used in both strings from same tin. All adjustments identical for both strings. Only thing that changed was the outcome, higher velocity and a higher spread with the 18″ barrel.
For example:
10 shot avg. of 879.0fps w/ 12″ barrel for 36.8fpe
10 shot avg. of 1009 fps w/ 18″ barrel for 48.6fpe
highest velocity was:
890.0fps w/ 12″ 37.8
1031 fps w/ 18″ 50.7fpe 😈
Anyone have ballistic info on how i gained so much velocity? 90fps would be the norm with such a change out. Its almost as if i put in a 24″ if we go by the numbers.
Next is to find out where the sweet spot is with this configuration. I’ll have to turn the tophat in to offset the extreme spread, which was large at 48.8fps vs. 23.3fps with the 12″ barrel. Other then the spread which is a easy fix i’m very happy and will keep her where shes at. Its a good velocity for a Kodiaks or Eunjins while still having a semi compact setup. I have a 6″ shroud which keeps things quiet, its worth the trade of for a 130fps increase in velocity.
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KM, i believe its all in Blodnobs valve, yes its still the 18″ barrel, and it goes to show that i was wasting a bunch of air with the 12″. Research would indicate that i’d would normally have just gained 90fps with such a changeout using a talon or condor valve. I have no intention of ever going to a 24″ just to dam long for my tastes, the power and short carbine look is why i choose the AF platform to begin with. I’ve yet to fine tune it for consistency, but would guess i’d loss the topend velocity maybe down to 1000-990fps to start with which is fine as i’d have a tighter string and more shots. Still after 25 shots i was over 900fps, but is was dropping quick. The advantage of Sean’s valve is you can adjust the tophat for travel, as well as screw in a restrictor which can reduce to ir lost for lower velocity shooting. The tophat has a huge range of travel so fine tuning is pretty easy. What else can i say the valve speaks for itself, i can only guess what a .25 barrel would yield. I should ask Beargreese as he has the same valve and a .25 setup.
Update! The 930 was with a 2400 psi. fill. With 2800, she went 1003 first shot-then 990’s for tha nest several shots! Yea!!! I need her to be able to do this with the Kodiaks”s!
Mike
Wow! Thats impressive BD! I’m getting only 930 fps with JSB’s in the 18″ bbl. I wonder how the condor valve compares to the bn valve. Should be close! I’m looking forward to seeing a shot string with your new set-up!
MIke
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Mike
Hey can you build me a bayonet for my Talon??
I may have to finish off a rabid skunk or chupacabra down here in South Texas.
Take Care