Tuning Low fps the first 10 shots FX impact mk2 compact.25

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asgardpark

Member
Apr 27, 2021
25
10
VBG, Sweden
Hi!
I have a weird problem on My impact mk2 i need to shoot about 10 shots befor it get Up to Speed if i left it over night.
Its currently tuned to shoot 30grain h&n slugs in 932-935 and the regulator is about 135-140bar the Valve adjuster between 4and3 and hammer is set to match the regulator. When i left it over night it usaly shoots around 910 and climb up to 935 in 10 shots.
The regulator stays on the same pressure all Night. I tested to degas the gun before I shot it and the it shot about 925 but still I hade to shoot a couple of shots befor I get up to speed.
Any one got an idea what am doing wrong?
//Daniel
 
Here’s a link to the lengthy thread where we troubleshot and brainstormed on the issue:

Tuning - FX Impact Mk2/M3 - slower first shot - no reg creep - quasi-scientific analysis

Hi guys, Welcome everybody. This is my first post here. I have a problem with my Impact Mk2 PP .30. The reg pressure is 145 bars. When I shoot shot after shot then my v0 is 260m/s. However, when the gun sits for a couple of hours then the first shot is 250m/s despite the exact same reg...
www.airgunnation.com www.airgunnation.com
 
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asgardpark said:
Hi!
I have a weird problem on My impact mk2 i need to shoot about 10 shots befor it get Up to Speed if i left it over night.
Its currently tuned to shoot 30grain h&n slugs in 932-935 and the regulator is about 135-140bar the Valve adjuster between 4and3 and hammer is set to match the regulator. When i left it over night it usaly shoots around 910 and climb up to 935 in 10 shots.
The regulator stays on the same pressure all Night. I tested to degas the gun before I shot it and the it shot about 925 but still I hade to shoot a couple of shots befor I get up to speed.
Any one got an idea what am doing wrong?
//Daniel
Click to expand...
 
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Thanks for pointing me in right direction!
I managed to solve my issue by changing the pur90 oring to an nbr90. My valve rod had a very rough surface so I polished it and i added a huma hammer weight and huma hammer spring. I also noticed that the valve return spring was in bad condition so i swapped that to. After the first night it shot 884fps with the king heavy mk2, waited 2 days the first shot was 886fps, took a shot this morning 884fps.
 
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asgardpark said:
Thanks for pointing me in right direction!
I managed to solve my issue by changing the pur90 oring to an nbr90. My valve rod had a very rough surface so I polished it and i added a huma hammer weight and huma hammer spring. I also noticed that the valve return spring was in bad condition so i swapped that to. After the first night it shot 884fps with the king heavy mk2, waited 2 days the first shot was 886fps, took a shot this morning 884fps.
Click to expand...
Initially I did the same. With high powers it works. The reason being the NBR doesn't get flexible after some use hence not notable extrusion.

The other way is to increase the hammer strike and restrict the valve travel by tightening valve adjuster.

But ultimately the comfort I had with FX impact mk1 with O ring from front style plenum could not be achieved specially with 18 grain .22 pellets.

So I made the front plenum part in mk1 style. It took some time to break in but after breaking in, I enjoy my M3 much more than before.

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asgardpark said:
Thanks for pointing me in right direction!
I managed to solve my issue by changing the pur90 oring to an nbr90. My valve rod had a very rough surface so I polished it and i added a huma hammer weight and huma hammer spring. I also noticed that the valve return spring was in bad condition so i swapped that to. After the first night it shot 884fps with the king heavy mk2, waited 2 days the first shot was 886fps, took a shot this morning 884fps.
Click to expand...
Did you add the PEEK backup washer? My M3 is still all stock and I’m getting 30-40 fps low on first shot. Takes at least 5 shots to get back up to set velocity.
 
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There are a couple ways to try to skin this cat but probably only two ways to do it properly. If you decide to try to overcome the sticking stock PUR oring by blasting it with a heavier hammer and spring, you’re going to have to control that with your valve knob. If you’re not shooting with very high reg pressures, you’re going to punish the valve spring and if you have a M3 the rubber balls also. If you just stick a Viton or NBR oring in there without a peek washer, that things lifespan is going to be short. That’s why FX used that big nasty PUR. It can handle extrusion without coming apart. So, either you peek washer/90 it or replace the plenum piece with a mubhaur piece.
 
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Seeker said:
Actually that PUR90 oring suffered from extrusion in my case. I even posted a picture of that in the mentioned thread. A peek washer or mubhaur's plug is a must regardless of the oring used.
Click to expand...
Yes but the PUR won’t fail as quickly as a Viton or NBR if you skip the peek disc. I am kinda curious how long a NBR 90 will last being pressed into that cone by 140b.
 
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