Tuning my Impact MKII for .25 cal FX Hybrid Slugs

[m021478]

I'm about to tune my FX Impact MKII with Power Plenum (700mm, .25cal, with STX Superior Liner) for the .25 cal FX Hybrids Slugs and I was hoping you guys could weigh in with your thoughts on the "ideal settings" (just to give me a baseline idea of where I should be at). I know all Impacts are different and that your settings might not be best for my gun, but I'd still like to hear what you've found works best. 

What FPS works best with these hybrid slugs? What pressure should my regulator be set at? What about the hammer spring? Valve adjustment knob? etc?

There's almost too much information with too many conflicting perspectives on this subject on these forums and on YouTube that it's totally overwhelming. I guess I'm just looking to get a sense of what you guys have found works best so that I can use that to get me in the ballpark.

Any feedback would be sincerely appreciated. Thanks!

 

[2L8]

Watch this first. It's 15 min long.

https://www.airgun101.com/index.php/component/allvideoshare/video/discussion-ultimate-25-cal-fx-test-5-barrels-5-projectiles-st-stx-slug-a-superior-sup-h?Itemid=362



2L8

 

[m021478]

I've already watched that video, as well as the other two 2 videos Ted recently posted comparing all of the various FX liners.

Most I was able to gather from Ted's video was that the Superior liner is the probably the best (most versatile) liner, that the Superior liner works great with Hybrid Slugs (Grade A), and that Ted has found that hybrids shoot best out of the superior liner at 985fps with his hammer spring set to 4.

But I was left with a lot of questions after watching his video, because pretty much every element of his configuration differed from most other tuning videos I've seen (such as

https://www.youtube.com/watch?v=KDvuMwjwk9M

and

http://www.youtube.com/watch?v=pTSTkC9ACK8

For example, Ted mentions that he leaves his regulator pressure at only about 95, and that he leaves his valve adjustment knob all the way out at 4 lines, and that he leaves his hammer spring crazy loose (with more play that I've every had out of my hammer spring).



Several other tuning videos suggest it's best to max out the hammer spring to keep the regulator pressure as low as possible will be ideal for air efficiency; other have found that the regulator pressure should be set to something between 135-145, and that the valve adjustment knob will probably wind up right above 3 lines or so. I guess I was left with more questions than answers after watching Ted's video.

I was hoping that in this thread, others who have an FX Impact MK2 with PP and a 700mm barrel shooting .25cal slugs could tell me what tuning configuration they've found produces the most accurate and consistent results. Thanks!

 

[nitrowoodtic]

I’ve been working on this myself. Not with great success either. I did find that my gun with 700mm Superior liner will shoot the NSA 29, 29.5, and,33.5 grain slugs very well at 40 yards. Problem is, I only get 10-15 shots before the groups get ugly. Cleaning the barrel brings it back for another 10-15 shots. I get hundreds of shots with pellets before it needs cleaning. 


As for the hybrids, 975-950 FPS seemed to do best but the groups were never very impressive. Could have been barrel cleanliness was part of my problem. 


My MK1 impact has the power plenum installed. I tested at 95-100, 125-130, and 145-150 bar measured with an EDMU. My reg didn’t like the 145-150 bar range and for what it’s worth, it didn’t shoot any better than either of the other two settings anyway. I think it was worst and much more violent. I think I might have hurt my reg testing at 145-150 bar. My FPS readings seem most consistent with the valve adjuster at 4 lines or a little more.

I was shooting the NSA’s at 900-925 FPS. And was getting one hole 5 shot groups. The third group would start to open up. With a very dirty barrel the NSA 38.5 grain had the best 100 yard grouping at about 2 1/2 inches at about 880 FPS and 125 bar reg pressure 


I still have more testing to do but at this point my gun is just way more predictable with pellets. 

 

[Bob_O]

My 700mm 22 Impact gets good accuracy no matter how I tune it. Last tune I did was in the field when visiting Steve......no Chrono, just sound and group size.

There is no single way to tune and no magic settings that one should use. Best way to tune for velocity when you are first starting out is by using the method in the Master Class video by Ernest Rowe.

Once you start understanding how it all works, what does what, you can then do different tunes for different calibers very quickly with excellent results.

 

[qball]

Why hybrid? You have the superior liner, get some NSA and shoot like laser at 800 and more FPS, very little tuning is needed. My 600mm .22 superior liner shoots NSA 23 and 24.8 grain slugs like laser at almost any speed. Haven’t had the need to try other weight slugs. Heavier .25 slugs are just Too much overkill for rabbits that we can hunt here. 

 

[Macloaded]

I have the same setup and I am currently shooting the 25cal hybrids at 930ftps. Reg is on 110bar and valve at just past three. Haven't measured the hs but only added four turns from stock to get it were I wanted it. I tuned for the jsb heavies at 850ftps but it also shot the hybrids lights out to 70 yards (the furthest I have tested so far). The superior liner seems very versatile, I will be testing more slugs soon and will probably have to up the reg pressure but happy with the hybrids at 930ftps. I read 930ftps to 970ftps is the sweet spot for them but I never got above 950ftps as the accuracy was spot on from 930ftps.