My M3 performed flawlessly for the first several months after I purchased it (except for a reg creep issue that was resolved after replacing the regulator). I was using it about 2 days per week during these firs several months. I had it tuned to 1/2” groups at 50 yards with the 2nd reg at 150bar and velocity at 990fps +/- 5fps.
And every time I took it out it was dialed in. But I did noticed that whenever I took it out after it had been sitting for a day or two that the first 3-4 shots were a bit slow, maybe 10-20 fps slower than where it had been the last session (990fps). The first 3 shots would be something like 970, 980, 990. I read that this is normal since it can take a few shots for the regs to “wakeup” and settle.
I took a break from shooting during the past 2 months. I did not make any changes to the gun doing this time. It just sat in its case.
The other day I took it out to shoot. I took out the half used container of Javelin slugs that I had been using the last time I had shot it - when everything was working perfectly. I checked to make sure that the reg pressure, valve and hammer were all set to where they were they had been when the gun was dialed in at 990fps. The first 5 shots were around 940. Over the course of 20 shots the velocity eventually climbed to 990. I thought maybe this was normal for a gun that had been sitting for 2 months.
I took 10 a minute break, then went back to shooting. The first shot was 960, then over the course of 10 shots it climbed back to 990. This is not how it behaved before. If I had taken a 10 minute break 2 months ago, there would be no change in velocity
The next day I took the gun out again and the first shot was 930fps. 15 more shots and it’s back up to 990.
Any ideas guys?
UPDATE: PROBLEM SOLVED
SOLUTION(S):
I did several things, all addressing the issue of friction on the valve rod. I made all of these changes at the same time because I didn’t want to disassemble the rifle, make a change, reassemble, let the gun sit overnight, test, then repeat the process for each change. As a result I’m not sure which change had the most significant effect on resolving the issue, but all of these changes could only help resolve this problem in the present and prevent it from happening again as quickly in the future.
For reference here’s a link to the FX Impact M3 schematic:
https://fxairguns.com/wp-content/uploads/2021/04/F10370-Impact-M3.pdf
I disassembled the gun down to the valve rod and on the 2 inch section that slides in and out of the Valvetube End (part 10338) there was a grippy grey residue. This was from the o-ring (part 19768, O-ring 2.84x2.62 PUR90) in the valvetube wearing away onto the valve rod, perhaps due to just normal use, not enough lube being applied at the factory, o-ring shrinking overtime - likely multiple reasons.
I did several things to reduce valve rod friction. I did more than necessary. Most people experiencing valve rod friction could likely fix it by cleaning and lightly lubing the valve rod with silicone oil.
What I did is excessive, but in the long term may require less frequent maintenance:
As described in the original post, before these changes the first 20 shots would be slow: starting at 100 fps slow and gradually increasing with each shot. And if the gun sat for just 10 minutes the fps would drop by 30 fps.
And every time I took it out it was dialed in. But I did noticed that whenever I took it out after it had been sitting for a day or two that the first 3-4 shots were a bit slow, maybe 10-20 fps slower than where it had been the last session (990fps). The first 3 shots would be something like 970, 980, 990. I read that this is normal since it can take a few shots for the regs to “wakeup” and settle.
I took a break from shooting during the past 2 months. I did not make any changes to the gun doing this time. It just sat in its case.
The other day I took it out to shoot. I took out the half used container of Javelin slugs that I had been using the last time I had shot it - when everything was working perfectly. I checked to make sure that the reg pressure, valve and hammer were all set to where they were they had been when the gun was dialed in at 990fps. The first 5 shots were around 940. Over the course of 20 shots the velocity eventually climbed to 990. I thought maybe this was normal for a gun that had been sitting for 2 months.
I took 10 a minute break, then went back to shooting. The first shot was 960, then over the course of 10 shots it climbed back to 990. This is not how it behaved before. If I had taken a 10 minute break 2 months ago, there would be no change in velocity
The next day I took the gun out again and the first shot was 930fps. 15 more shots and it’s back up to 990.
Any ideas guys?
UPDATE: PROBLEM SOLVED
SOLUTION(S):
I did several things, all addressing the issue of friction on the valve rod. I made all of these changes at the same time because I didn’t want to disassemble the rifle, make a change, reassemble, let the gun sit overnight, test, then repeat the process for each change. As a result I’m not sure which change had the most significant effect on resolving the issue, but all of these changes could only help resolve this problem in the present and prevent it from happening again as quickly in the future.
For reference here’s a link to the FX Impact M3 schematic:
https://fxairguns.com/wp-content/uploads/2021/04/F10370-Impact-M3.pdf
I disassembled the gun down to the valve rod and on the 2 inch section that slides in and out of the Valvetube End (part 10338) there was a grippy grey residue. This was from the o-ring (part 19768, O-ring 2.84x2.62 PUR90) in the valvetube wearing away onto the valve rod, perhaps due to just normal use, not enough lube being applied at the factory, o-ring shrinking overtime - likely multiple reasons.
I did several things to reduce valve rod friction. I did more than necessary. Most people experiencing valve rod friction could likely fix it by cleaning and lightly lubing the valve rod with silicone oil.
What I did is excessive, but in the long term may require less frequent maintenance:
- CLEANED the valve rod with rubbing alcohol
- POLISHED the valve rod using a polishing compound and microfiber cloth to polish the valve rod until it had a shinny mirror-like finish. Took about 10 minutes. I used Flitz Multi-Purpose Polish and Cleaner, available on Amazon: https://www.amazon.com/gp/product/B000MUSOW4
- LUBED the VALVE ROD with silicone oil.
- UPGRADED THE VALVETUBE so that it has a PEEK SPACER/BUSHING inside the valvetube next to the o-ring (part 19768). The valvetube that comes stock on the M3 doesn’t have a threaded end that allows it to be removed so that the two o-rings inside the valvetube can be easily accessed. It was difficult to replace the 2 o-rings inside the valvetube. The stock valvetube also doesn’t have a high strength spacer/bushing to support the sealing function of o-ring 19768. The peek bushing also ensures that there isn’t any metal-on-metal contact between the valve rod and the valvetube. For these reasons I purchased a custom valvetube from AGN member mubhaur which has these features. He explains the rational for his design in the video below.
As described in the original post, before these changes the first 20 shots would be slow: starting at 100 fps slow and gradually increasing with each shot. And if the gun sat for just 10 minutes the fps would drop by 30 fps.
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