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

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Hi guys,

After more than 48 hours there is no issue with the first shot. It is well within standard deviation when I count the next 10 shots.

Now I am going to inspect Viton80 oring to check if there are any signs of extrusion. After that I will replace Viton80 with NBR90 to check if it works fine as well.

I am really happy this mod seems to be promising. 
 
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Hi guys,

After more than 48 hours there is no issue with the first shot. It is well within standard deviation when I count the next 10 shots.

Now I am going to inspect Viton80 oring to check if there are any signs of extrusion. After that I will replace Viton80 with NBR90 to check if it works fine as well.

I am really happy this mod seems to be promising.
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Great Seeker,

My RAW valve also had a lot of room for extrusion. I just handed over it to the machinist to install a peek made guide with the required clearance with the valve stem.

I hope it will fix the issue.

Further I am also going to replicate your mod in my M3.

Thanks for your R&D.

Bhaur
 
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The mod didn’t help my Impact. First shot 905, then 921, 927, 931, 928, 930, 926… I would like to add that I have the stock 2 orings in there. I didn’t switch the fat one to a different compound. Not sure what I’m going to do next. My gun is also fighting me getting back onto my original slug tune.
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I would switch at least one oring if not both to a different compound and give it a try the testing done earlier showed the original would stick under atmospheric air pressures and if everything is still moving like it does it'll stick or your dimensions aren't tight enough fitment wise I would try different orings first can't get fps back up to where it was or what ? Seekers mod was in a MK2 I believe is yours a m3 possibly different dimensions ? 
 
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No, I did the mod to my M2. I was hoping that the PUR oring wouldn’t be a problem if it wasn’t getting pinched. I finally got the gun shooting perfect tonight with way different settings than before so I’m reluctant to tear into it again until I absolutely have to. Don’t get me wrong, I like to shoot but sending 300 slugs to slug heaven trying to find that pin hole where they shoot fantastic is getting old and expensive. I will see what oring Seeker likes and grab some for when I’m in the gun again.
 
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By me using the PUR oring, at least one thing is clear. It’s not the conical cut in the plenum plug causing problems. It’s the choice of oring material needed to deal with that conical plug.
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But in the pics Seeker shared, his PU O ring was extruding without his mod. I can understand that conical area may not be creating the issue but loose fitting may be causing extrusion which would have been fixed by putting a good Clearance peek disc.

A close Clearance peek disc should address the extrusion issue.

Further other than PU material may be less sticky. 

Bhaur
 
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The root cause of this problem is oring stiction increase over valve inactivity time. Here are the factors (among others) contributing to that phenomenon:

- oring extrusion - the role of a peek washer is to eliminate that by tighter tolerances. I treat it like a back-up oring,

- oring compound - the worst one seems to be PUR then NBR then Viton,

- oring hardness - softer compounds lower the stiction,

- plenum pressure.

We can only truly eliminate the first factor. Others can be minimized but not eliminated.

Here is some more info on friction:



It comes from ERIKS Technical Handbook O-rings.

I examined Viton80 oring and I noticed no extrusion signs. I installed NBR90 to verify that compound and increased hardness.
 
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I can’t wait to see how the NBR90 works as I’m not a fan of Viton. I thought about it and will probably take my gun apart again. It would be foolish to have built the peek disc, have it in my gun and not reap the benefits of it. It was my fault for getting side tracked with my mysterious velocity gain that caused me to use so many slugs chasing my old tune. I should have stopped right when I saw the PUR and peek disc combo didn’t work. I’m also curious if my new settings for accuracy will work if I completely disassemble the gun again.
 
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