JSB Knockout 22 cal 25.4 gr VELOCITY

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The upper end of the spectrum you’re describing is 56fpe. That is no small feat in .22 cal. You are at almost 46fpe at the moment which is nothing to sneeze at. 

To get more, you will need some combination of the following:

1. Longer barrel
2. Larger porting
3. Larger plenum
4. Higher pressure

If you don’t know where to go from here, my suggestion would be to give a little detail on where things stand with these 4 items and these guys will get you pointed in the right direction.
 
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I’ve found 935 to 940 the sweet spot. I suggest bumping the reg press up a little and then fine tuning the valve. The valve adjustment should be made as carefully as you can. Shoot three shot groups at about 35 yards. When you get to shooting three into one hole then move out to 100 and see if you don’t have what you are looking for. You are using the 217 diameter slugs correct ? 
 
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You can still get good accuracy below 900 fps, but won't buck the wind as well as higher speeds:

Screenshot_2021-02-22-12-02-27.1614013534.png



 
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You did not indicate if you had adjusted the hammer spring. You said you were on the max setting which is where you will most likely need to be.

I have the MKll with the power plenum and with moderate hammer spring and the power wheel on MAX with the valve on about 1-1.5, yes, almost all the way in, and with a the pin probe/slug power kit and Earnest's dual hole transfer port with my regulator on 115 bar and the Superior liner, not the heavy liner - I pushing JSB monster redesigns 25.39gr at 953 fps quite easily. The FX Hybrids with the same settings are around 985 fps. I suspect this is mostly due to the dual hole transfer port and the slug power kit.
 
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The best money I have spent on my Impact Mk2 to get speeds up at lower regulator pressures was to install the Fx pin probe and the dual transfer port.
These after market items resulted in an increase of between 50-60fps without adjusting the hammer spring or valve.

For my rifle I have found the sweet spot for the JSB NO’s .216 is between 980-990fps 
 
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Brandon-Vet said:
I have the veteran II 700 in .22. What is your max FPE?
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Oh ... old thread. Readers digest - when I was running slugs with that one on a modified 700mm "slug barrel" ( I had it cut down to 600 and re-crowned and then I polished it myself ) it would up being a 44'ish fpe with 23g H&N .217's running around 935. Stupid accurate - shot count though - 'eh . . .

You've got the newer model - presumably more (natively) friendly to slugs, I believe they have more air capacity, higher cap too (300bar?) - I would assume you should be able to get good performance out of it so long as you can find a slug it likes. I've since reverted mine back to 18g pellets with the oem barrel, dropped the reg down - getting 60+ shots out of it now and still very accurate.
 
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That's great! I'm glad you could get the desired results with accuracy ( I couldn't imagine doing all that to my barrel.

I'm running 25.39 JSB knockouts slugs around 930 without touching anything. I may just keep it there with 100-yard tight groups.

However, I am curious if I should use heavier gr slugs and up the hammer spring for a small game—more impact - more humane kill.
 
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