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Slow FPS Impact MKII (23gn NSA)

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shatafire

Member
Oct 7, 2015
52
0
WA, United States
Sold my mk1 impact two weeks ago for Camaro parts. My wife surprised me with money for another pcp because a raccoon killed her young chicken. Anyways, I had fps problems with my mk1 shooting 18gn jsb pellets slowly until I tightened the power dial and installed a Huma. After which the gun was perfect. Too bad I had to do this, but happy afterwords. 

I just received my mkii from Joe B which I bought specifically to shoot .23gn Nielsen slugs. It struggles to push these at 885-900fps even with the reg as high as 170. 

Am I the only one caught in the Mkii hype? I was expecting decent speeds without going above 150 bar. I have both the slug and x liner. 

I talked to a tech at FX USA because my slug liner wouldn't fit and I refused his suggestion to sand it down. I bought a different one that fits, but the tech told me that he finds that the 23gn Nielsen slugs max at about 860-875fps for him also. 

I think I've been whipped into the Dubber/Air Hunters hype tornado. Are those guys cranking their regs or what? My assumption is that they are because Matt said he is getting about 30 usable shots shooting 30gn. If this is the case I wish they'd state so with all of their other verbal disclaimers. 

Does this sound weird to any other impact owners?
 
Have you adjusted the hammer spring pre tension adjuster or the valve adjuster? You have to adjust it for the slugs being shot. Should be able to get them going faster than that. At 170BAR your probably don't have a heavy enough hammer/hammer spring to open the valve for FPS gains. Try this...

Start at 150BAR, open the valve adjuster past 4 lines and tighten the hammer spring pre tension adjuster until it's almost causing the power wheel to not turn while on max., then back it off just a hair. Should have plenty of power for 23gr. slugs. You should be getting a lot more than 30 shots too. 
 
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what is the length of the slug liner?
Click to expand...

Mine is 700 mm and shooting the 24gn slug @ 925 fps at 140b out of the box so probably is a 600mm

@shatafire you need to adjust the spring tension screw if you change reg pressure as stoti mention. You should be able to shoot @ 930fps the 23gn the mk2 just tuning.

You can also make some changes or mods, best one on 0.22 is elongated transfer ports

More about mods

https://www.airgunnation.com/topic/fx-impact-mods-for-more-fpe/




 
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Loosen the barrel retainer screw 1/4 turn, rotate the barrel side to side to find the middle of the alignment slot and tighten the screw at the center point. This will align the brass transfer port better. Flaring the entrance of the brass transfer port back to the edge of the o-ring will eliminate alignment issues and give more velocity in .22.

Here are the results when I first installed a 700mm slug liner in my gen 2 Impact. My transfer port is modified. Don't judge the gun by my groups because I'm a better mechanic than shooter.

1558023978_1360183875cdd8f2ade2486.74761980_22 slug test 1 -.jpg


Modified transfer port and pellet probe...

1558024706_17316826465cdd920245b3f2.61775667_port1 -.jpg

 
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600mm



I everhave tried everything except enlarging transfer port. As mentioned before, this isn't my first rodeo with an impact, so I know about the possibility of adjustments out of the box, BUT this is the MKii so I wasn't expecting the same underwhelming performance issues with a refined gun. 

Thank you all for the ideas. I will sort it out and then post the fix for the next guy who experiences this. 
 
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600mm

I everhave tried everything except enlarging transfer port. As mentioned before, this isn't my first rodeo with an impact, so I know about the possibility of adjustments out of the box, BUT this is the MKii so I wasn't expecting the same underwhelming performance issues with a refined gun. 

Thank you all for the ideas. I will sort it out and then post the fix for the next guy who experiences this.
Click to expand...

Performance wise there's nothing different about the MKII other than the larger plenum that isn't needed as much in .22

The new custom Wika gauges and side shot mag are nice benefits for the same price as the old version but .25 and up with a larger valve and port work is where the MKII will shine.
 
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600mm

BUT this is the MKii so I wasn't expecting the same underwhelming performance issues with a refined gun.
Click to expand...

At 145bar, my Crown (600mm barrel) was shooting the 24gr slugs at 903fps.....hammer spring adjusted properly of course.

So you're saying you adjusted the hammer spring tension for max velocity and still struggle to get 900fos with 23gr slugs? Did your previous Impact develop good power?

The MKI Impact is a 50fpe fun out of the box. The MKII is 60fpe out of the box.....22 caliber I'm speaking of. If you're struggling to make 45fpe with a MKII, either something is wrong or you're doing something wrong.

Have you followed Ernest's new video to a "T" and that's all you can get?
 
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The MKI Impact is a 50fpe fun out of the box. The MKII is 60fpe out of the box.....22 caliber I'm speaking of.
Click to expand...

I respectfully disagree, with barrel lengths being equal. The only difference is the larger plenum on the MKII and the MKI was large enough for .22

I can't see there being more than 1 or 2 fpe difference between them out of the box in .22 depending on barrel length.

I still have the original plenum size and get high velocity on low pressure in .22. As you go up in caliber you get a larger pressure drop on the plenum because you're filling a larger space in the barrel. The larger the caliber the greater the benefit from a larger plenum.

Just as in turbocharged engines you get more power from easing airflow than from adding more pressure and the MKII restrictions are exactly the same as the previous generation.

Same valve size, same port sizes and same sharp 90 degree turns.
 
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So I just took the gun completely apart and reassembled it. I am now getting 950fps maxed out with 23gn. This will do fine. 

I wish I knew what the exact culprit was, but I did find many screws (5) loose (finger loose) upon disassembly. I also moved the pellet probe block closer to the front at 45mm from the back end of buttplate. 

Fortunately I had experience taking things apart from my MK1. 

I'd already tried everything in every video ever posted about this rifle. I guess a complete reassembly is what it wanted. 

Thanks for all of the support guys. 


 
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I should mention those figures are with 700mm barrel.

The current Impact can send a 26gr slug at 950fps.

The MKII can send a 30gr slug at 950fps.

No?
Click to expand...


I haven't tried unported but edosan could probably answer the question. I don't think an unmodified MKII will send a 30gn at 950 but my gen2 with the port work will send a 30gn well past 950.
 
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IMO

30gn 0.22 @ 950fps stock mk2, don't think so, 25% larger plenum is not enough. All the rest is the same than old ImpactX. Even @ high reg pressure. Small mods needed, like elongated tps, hammer weight and reg @ 160-170 ... adding the VS bigger bore like 6.3mm and reg @ 150-160 , and if you add an external plenum 140-150bar probably. I doubt a 30gn slug will go over 900-920 fps on a stock impact mk2. 22 up to 27gn should be the weight for a stock mk2 impact slug (just educated guess have not tested really, since I only test the 23gn (or 24gn don't remember) only out of the stock mk2. 

Just elongating ports there is a gain of about 50fps depending on the weight of the ammo.
 
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