Tuning Impact MK 11 accuracy

[Rockhound1]

Any one having accuracy issues in 25 cal. I cant seem to get to shoot jsb or slugs good. It shoots fair at best. I have a wildcat mk3 in 30 cal that I tuned that shoots 1/2 inch groups at 100but cant get .25 cal to shoot for heck. I have tried various speeds from 750 fps to 1000 fps and pellet weights from 25 grain to 34 grain.

 

[Riss]

A mi me pasa lo mismo , creo que no sintonizo la velocidad adecuada . Mi carabina es una fx impact mk I con powwer plenum y superior liner de 600 mm.

Que hago mal ?

No logro subir la velocidad de 912 Fps con jsb exact king heavy mkII Y Nocks Out 

 

[Odoyle]

Dirty barrel?

If not-

Breech o-ring still there?

Check you pellet probe if it's loose or not seating pellets properly.

If still no good-

Check your barrel Tensioning nut and try removing the o-rings. 

900-930fps with JSB Kings 25.39gr work like magic.

You can try swapping to a different magazine too just in case.

 

[biohazardman]

 

edit;

If the other things are taken care of.

My MK1 with 700 STX slug A liner shoots < MOA at 100 yards with several projectiles at 740-960fps. But my new 500mm Superior .22 liner was like > .75 inch at 50 yards at it's best for the most part.

https://www.airgunnation.com/topic/barrel-and-slug-comparison-stx-vs-superior/page/2/?referrer=1

 

[Vetmx]

The impact is a checklist gun. Never fired a pellet out of mine at a target but no problems with slugs so far. When I say checklist, I say it to prevent aggravation. Clean barrel, liner nut always tightened to the exact same tension, liner orings either secured so they don’t move or CF sleeve. Working your way up or down with an Allen wrench to find your true max speed with your reg setting with the VLA wide open. Then back the spring off to slow it down a little then do the same with the VLA. That’s my starting point before i shoot paper. I do it all again if I bump my reg up. No shortcuts. If you cross all your T’s and dot all your I’s before you start shooting and you still have accuracy issues, at least you know you weren’t cutting corners to get a good tune. Time to start looking at parts. 

 

[Rockhound1]

My wildcat is great out of case every time.I just shoot it. If impact is that finicky that I guess I got an impact for sale. Barrel has been check with and without o rings. It has been cleaned. I use several mags so that is ruled out.

 

[biohazardman]

I go through a checklist also but only when I have troubles with my Impact. Troubles which rarely occur but when they do are most often of my own making as I am constantly tinkering. 

 

[Odoyle]

Is the liner pointed in the correct orientation?

 

[Rockhound1]

Barrel is installed correctly and pellet probe is tight.

 

[Vetmx]

How do you tune your gun before you start testing for accuracy? If you are just adjusting the reg and spinning knobs hoping to get lucky, that might be the problem. It can happen and I’m sure it has but that barrel system I believe is a little more sensitive to having the projectile leaving it with just the right amount of air behind it. I can get away with a jacked up tune and still have decent accuracy with my RTI because the barrel is thick and has a super rigid mounting platform.

 

[Redick]

Clean that liner/barrel really good and shoot kings if it doesn't shoot the kings you have a lemon!

 

[Rockhound1]

Ordered new barrel liner. Found small spot in crown. Probably not issue but going to try. To vetmx the gun was bought used and jacked up when i got it.Accuracy is 2 inch groups at 50 yards at best with jsb 25 grain currently.

 

[Vetmx]

Yikes!! If you bought it used, I would start from scratch on a tune and do it the right way. A new liner is not a bad idea. Even if it’s just for peace of mind.

 

[Rockhound1]

Kinda where I am Vetmx. Just looking for maybe something I had not thought of. Old liner has no tag or identification so really not sure of what liner it is. I know it is not original as seller told me he changed it to try to shoot slugs. Gun is an FX impact x Mk 2 with pp. Should be a stx liner but seller put a superior in it he said.

 

[Vetmx]

I have the same gun with a 600mm barrel. I would start with a very low reg setting and the JSB 25gr pellets. My gun will sling that pellet faster than it needs to go at 100b on the reg. As long as you follow the proper way to base tune an Impact, there is no reason that pellet shouldn’t shoot well.

 

[Rockhound1]

Once new liner gets here I will start there Vetmx. Reg set at 130 now as ive been trying to shoot the 33 grain jsb.

 

[Chuck-in-Ohio]

Vets advice is the way to go, start back at square one and proceed from that point. Your rifle is probably way out of whack and needs to be 'reset' to baseline.

Start at 100 bar as suggested and work up. My 700mm .25 Impact MKll is throwing the MK2 heavies at 965 with a 130 bar reg setting and STX slug A.

What length barrel are you running? 

 

[Rockhound1]

700 mm stx heavy on the way.

 

[california.airgun]

@rockhound1 i have 1 stx liner and 1 heavy superior liker for sale if you are interested.