Tuning Speed for JSB .22 Jumbo Heavy Diablo 18.13gr

[kball]

What speed have you found to be most reliably accurate for the JSB .22 18.13gr pellet? I realize there are a bazillion variables that could be considered when answering this, but please share your number what ever it is. I recently did a PP upgrade to my MKII Impact and the 935 +/- that was set up original from FX (AOA) doesn't seem to offer the same results as it used to. I have re-tuned 2 or 3 times but just can't seem to be able to get the repeatable tight 50 yd. groups I was used to b4 the upgrade.

 

[Khornet]

Don't think I've ever gotten very good results above 900-010 fps in mine; usually more like 880s-890s. What reg setting? Hammer? Valve?

 

[crazyhorse]

Tried two speeds:

AV 912.3

ES 10.5

SD 5.2



AV 879.3

ES 7.1

SD 3.74

 

[Smok3y]

880ish has been where mine is the best consistently day in and out. I have had some days where 930 seems like the best, but never as consistent as it is at 880-890.

 

[PumaCarl]

Yup 880ish!

 

[kball]

Reg = 90 Bar

Hammer = .682"

Valve = .250

 

[Khornet]

Kball, those settings are not far off from what I was using in a 700 mm barrel to shoot 23 gr H&N slugs at 910-920 fps, except your valve adjuster is closed a lot more.. And I was having problems with consistent velocity. Posters here told me I was overdriving the valve, that is, too much hammer for the reg setting, causing the valve to rebound hard and close the valve prematurely. Looks like you need a lot of valve adjuster to get your velocity down where you want it, so maybe you have too much hammer. I would back off the valve then decrease hammer then dial in accuracy with tiny valve adjustments. Or you could increase reg a little, say 95-100, so I balances better with your current hammer setting, then tiny valve adjustments.

 

[kball]

Thanks Khornet, I really did not realize the valve was closed as much as it is till I measured it (this is just where it ended up). I'll back off the valve and re-adjust to get to the 880 ish range and see what it does. Should there be play in the hammer adjustment plate? The last time I tuned it I tightened the screw until there was no play with the wheel on max. 

 

[gendoc]

888 from my dream-tac compact.

 

[Khornet]

Kball: https://www.airgunnation.com/topic/peculiar-observation-tuning-my-impact/?view=all#post-954235

Thread where I learned not to start with hammer on Max and screw all the way in. There are a number of similar observations floating around the forum. If you do it that way you get deceptive values because of valve rebound.

 

[Khornet]

Also https://www.airgunnation.com/topic/fx-impact-36/?view=all#post-959630