Tuning FX Impact oddities

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Yardstick

Member
Apr 8, 2022
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AZ, United States
I have a couple of strange things going on with a used FX Impact that I purchased recently. I think it's a MK1. It doesn't say MKII on it and it certainly doesn't say M3 anywhere. There are some little differences from pictures I'm finding but generally what I'm seeing aligns with an MK1 gun. Anyway, the oddities... 



The first time I pumped up the Impact with my Hill EC-3000 compressor I found that the gun was leaking air. The gun says it can be pressurized to 250 bar, so that's where I had set the compressor. According to the bottle gauge the gun was over-pressurized. Lots of articles say to trust the pump more than the gauge on the rifle but the air leak had me concerned that maybe the Hill pump was the issue. I have filled other rifles to lower pressures and the gauges on those usually agree with the pump's set pressure, so I think it would be a stretch to blame the pump. Anyway, I dry fired the rifle several times until it seemed like the leak stopped. I fired it a few more times to check other things and then a couple of days later tried to pump it up again. This time I set the Hill pump to 230 bar. When the fill completed the rifle was hissing again, but not quite so much. The bottle gauge indicated 250 bar. I'm suspicious of the gauge but what could be leaking?



The next oddity has to do with the regulator pressure/gauge and the velocity. At the maximum setting on the power wheel I'm getting pretty low velocity out of the rifle. After a fresh fill to 220 bar (no hissing), five JSB Jumbo Heavy (18.13 grn) pellets came out of the barrel at 156.9 m/s, 170.6 m/s, 172.7m/s, 175.9m/s and 174.5m/s. But the regulator pressure gauge indicated over 200 bar! Could this be another bad gauge or is there something else I need to look into? Where should I start trying to tune this rifle?
 
What could be leaking? Impacts have a lot of O-rings; any of them could be the source of a leak. The MK-I is an older gun, so you should consider a complete reseal. If the reg. pressure is 200 bar it's either set wrong, a bad gauge, or the regulator needs rebuilding. Chances are it's reg creep and it needs a rebuild.

I'll leave this to the Impact experts to comment further.


 
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Cheap gauges are cheap gauges sounds like I would trust the one on your pump first.

You may have a faulty reg, and creep to go with it, as hawkeye states.

I would clean it up and replace the o-rings that look bad and go from there.

I have a Mark one myself, with over 12K rounds through it, and the only o-rings I have actually had to replace were a couple that I damaged on reassembly after a mod.

Had a hard time getting the o-rings on the screw adjuster so I made this and it made installing the o-rings much easier. A little longer and more gradual cone to slide the o-ring up on would make it even better.


 
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It seemed like it was leaking from somewhere in the trigger guard area but there was so much air coming out that I couldn't pinpoint it. Now that I know a little more about how the rifle works, the regulator makes sense as the source of the leak. I still don't understand why the pellet velocity is so low. Wouldn't it be quite high if the plenum was pressurized to over 200 bar?



I actually ordered a power plenum kit since it seemed like a neat upgrade and the seller said that kit comes with all of the o-rings to completely reseal the rifle, including all o-rings for the regulator. Now I'm wondering if I should have just got the few o-rings I need for the regulator to try that first. It seems like either way the rifle is going to be down for a bit.
 
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I use this stuff on my Impact to find leaks: Amazon.com: CRC Aerosol Leak Detector, 18 Wt Oz : Automotive

Evaporates within seconds to minutes. For the leak, where is it leaking from? From the regulator vent behind the trigger = regulator job. that's probably the worst case scenario. I replaced my reg a couple years ago, and I think the replacement was $40 from FX.

Other than that, just spray away and eventually you'll find it, and then should be able to identify the proper rings to replace

You can tell if it is a Gen 1 by the logo on the block. The spiral representing the smooth twist barrel was only on Gen 1's if I remember correctly.
 
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Getting o-rings turned out to be more of a challenge than I anticipated. My local airgun dealer no longer supports FX airguns. They don't sell parts and it sounds like they won't even work on them. I ordered regulator o-rings from a dealer that does sell FX parts and received them about a week later. And fortunately it's not hard to find how-to videos. But the complications continued. The o-ring in the bore where the regulator seats would not come out with any tools I had. My smallest Harbor Freight picks were just breaking the o-ring into tiny pieces. I found some smaller picks and even some brass picks from Amazon that showed up in a couple of days. They finally got the job done but then I realized the o-ring that I had finally extracted was much bigger than anything in the o-ring kit! I figured that if it was going to be that expensive and that complicated to get a few simple o-rings, maybe an o-ring supplier would be easier to deal with. Now I have a lifetime supply of every o-ring for every rifle that I own. :D The regulator is re-sealed and the new gauges seem accurate so far. I pumped the gun up to 200 Bar to run a test and.... it's still leaking somewhere! I can't hear it or feel it but it has lost 60 Bar in about five hours. I may have to try the water/soap trick or pick up some of the CRC leak detector spray. Fortunately I know I have a replacement o-ring for anything that is leaking!
 
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There is a spreadsheet for the O-Rings needed for an MII and M3 located here....

M3 O-Ring/Schematic/Ordering Spreadsheet - Airgun Nation

It also contains an ordering sheet and a vendor that handles all of the O-Rings along with the contact information. Give it a go, the O-Rings are cheap enough to buy and you won't need to rebuy for some time.

mike
 
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There is a spreadsheet for the O-Rings needed for an MII and M3 located here....

M3 O-Ring/Schematic/Ordering Spreadsheet - Airgun Nation

It also contains an ordering sheet and a vendor that handles all of the O-Rings along with the contact information. Give it a go, the O-Rings are cheap enough to buy and you won't need to rebuy for some time.

mike
Click to expand...



Well that would have been helpful to have instead of making my own spreadsheet. Oh well. I ordered and received o-rings already so I should be good for a while if I can identify where the leak(s) is/are coming from.
 
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I'm just chasing leaks on this rifle! First it was the regulator. I got that sealed but it still lost pressure too quickly. I had to put it away and deal with some other things so I haven't looked at it in nearly a month. I finally had a chance to pump it back up and locate the next leak. It turned out to be the plenum gauge. There were two plastic washers in there instead of the proper X-ring. Now that gauge is sealed correctly. But the rifle is STILL leaking! It looks like the bottle adapter is leaking where it meets the receiver part of the gun. I didn't see that as an O-ring on my great O-ring purchase so now I need to hunt that part down or get it from FX or a dealer.
 
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