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

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Other thought would be bond peek insert to the rod on either side of the oring to keep it in place but would need to be into the correct place that way the oring couldn't travel into the cone and a tight fitting peek guide would hold it in place Instead of making a notch for oring to ride in spit balling again just trying to put ideas out there maybe inspire one of you guys that know more about the system
 
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You are right. PEEK would be better as PTFE can deform a little and grip the rod really hard - tending to jam it - it might be enough to have such a PTFE seal without an oring. It might last for a while. However, PEEK is far superior in abrasion resistance matter. It can also be filled with PTFE to reduce the friction even more.

If we do not want to modify current plug then such a PEEK piece will be needed so that it can enter the conical cavity a little (sorry for the lack of symmetry):



I think I will try to make it and test it.

What do you think?


 
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I have another potential solution which is somewhat similar to yours. However, it is much easier to implement.

We know that oring wedging caused by its extrusion seems to be the root cause of the first shot being slower after extended period of a valve inactivity under high plenum pressures. So ultimatetly we want to avoid this situation:



My idea comes from the pneumatics world as well. There as so called back-up orings preventing from oring extrusion: https://www.parker.com/Literature/O-Ring%20Division%20Literature/ORD%205700.pdf -> Back-up Rings – Section VI

I propose this approach:



The gap in the plug itself should be big enough to allow the rod to move freely. Its diameter can be about 0.05-0.08mm bigger than the rod itself. Next, a PTFE washer should be placed. It should be a tight fit over the rod and it should also be tight in relation to the external cylinder. The role of that PTFE washer is to be a backup oring. Next, we place some Dur90 oring - it can be the one suffering from stiction issues the least. We know that wedging will be eliminated with this approach. The rod will be guided by the PTFE washer, no longer rubbing the plug itself.

Sounds like a win win approach? Any weak points?
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I believe this is worth a try. If it’s successful, make sure you get 10,000 of those spec washers. When those guys over on the “Your M3 tunes here” topic finally quit worrying about someone else’s numbers and start to understand their guns, some of them will probably advance themselves enough to start nitpicking the guns flaws. I don’t plan to tear into either of my guns right now but if you find success, both of mine will be in pieces soon after.
 
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I am pretty sure M3 shares the same issue. However, I am not 100% positive as I did not have M3 in my hands.
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My M3 is starting to exhibit the same symptoms but the gun is relatively new. My M3 has been sitting for 13 hours now and I put it away last night and wrote down all my settings and speed. I will chronograph it now. My second reg did creep 1.5b but I don’t think that will distort what we’re looking for.
 
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I didn’t realize that our plenum plugs had a tapered cut down in there. That in itself with just orings is causing a pinch problem under constant pressure.
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Yes, they have it. It was referred as a conical cavity in my previous posts.

I am pretty sure M3 shares the same issue. However, I am not 100% positive as I did not have M3 in my hands.
Click to expand...

My M3 is starting to exhibit the same symptoms but the gun is relatively new. My M3 has been sitting for 13 hours now and I put it away last night and wrote down all my settings and speed. I will chronograph it now. My second reg did creep 1.5b but I don’t think that will distort what we’re looking for.
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Such a reg creep will not result in 20FPS+ drop of v0 in the first shot. I would say 1bar of a difference may result in 3-3.5FPS of a v0 difference.

I have a feeling that the issues become worse over time - PUR90 oring becomes more and more deformed and wedges more and more. Especially if we talk about 130-140+ bars of plenum pressure. M3 has a bigger plenum which should allow to reduce plenum pressure and result in less oring wedging.
 
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M3 150b second reg. First shot 900fps. Then 913, 909, 915, 915, 914, 911, 915, 910, 913. What’s funny is the gun is 7fps faster than when I put it away last night. Maybe everything just settled after switching from a 140b tune to a 150. It’s also just part of the Impact life but that’s for another topic. But my gun could possibly be off the wonderful slug tune I found last night. That’s where that mysterious +7fps can bite an Impact owner. I will check my 70yrd accuracy later tonight and see if it went south. 
 
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If I were to do this peek guide, and I might, I would put something like wax or clay down in there and make a mold. Then I would know the angle to cut on my lathe. I would also have to measure the rods diameter and find a bit for the hole. I don’t have a super duper micro boring bar to bore a 3mm hole. It’s doable. Maybe I will call FX and get a plenum plug. Then I can build it without taking my gun apart and see how it goes. Just not sure if I’m motivated right now. Being a shot dumper has spoiled me.
 
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I just got up. 

I still believe that I should use the mk1 set up. May be with the modification as mentioned by friends above. I mean that I should sandwich the PU90 O ring between the peek washers.

Then I see an other thing. That it is a normal phenomenon that a regulated gun gives the 1st shot at lower fps in almost all designs whether it be impact or some other.

To me the main issue is that mk2 gives 35 fps low in 1st shot and then the 2nd shot is not perfect either. 

It takes around 10 shots during which it gradually comes to the set fps.

So I think that may be we have changed the orientation of the main issue.

I understand that all the above mentioned techniques may be helpful in curing the real issue which to me is gradually coming back to the set fps in around 10 shots. But I think the 1st shot may still be low as it happens in almost all regulated pcp guns.

There may be other reasons of first shot going slow just like cold barrel effect in fire arms.

Bhaur
 
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