Tuning Help With Inconsistent Impact M3

[MikeAllen]

I used to achieve very tight ES (10 or under) and SD (2-3 or under) with my FX Impact M3. I am now getting ES of 40-50 on my first magazine, then it tightens up to around ES of 15 or so on the second mag. I also used to get short range MOA or sub MOA POI’s. It’s now some MOA but several fliers – short range being 35 to 50 yards. Overall, first magazine is about 2.5 to 3.5 MOA.

Barrel has been cleaned, breech o-ring changed, second regulator is consistent within 2-5 bar, internals cleaned and lightly polished (valve, valve spring, spring guide, valve rod). Pellets are all washed and sorted by weight. The puzzling thing is that it tightens up some after one magazine (25 shots.) Can anyone tell me what I might be overlooking?

Here’s the setup:
Impact M3 standard (600mm) with unmarked power block (s/n 216xxx)
.25 caliber – shooting FX and JSB 33.95 grain pellets – washed and sorted by weight.
Macro 16, Micro +/-3.5, valve about 4, second reg 120 – these are factory specs for this pellet.
First regulator replaced with Saber Tactical first reg bypass.
Standard internals (hammer, spring, etc.)
Average velocity 872 fps when ES is tight - 830 to 900 on first mag now, then it tightens up.

Any help or suggestions will be helpful, especially if you have experienced this same situation.

 

[7Green]

Have you checked the orings in the barrel or the small oring at the end of the valve? The one at the end of the valve you will hear and feel with your cheek if it blew.

 

[7Green]

By orings in the barrel, I am referring to the transferport area and not physically in the liner. Figured I better specify.

 

[DBlue]

I had problems with the 1st reg. on my new MK3 and I installed the Saber Tactical bypass also....I set the 2cd reg to 130, turned the macro wheel to 16 then turned the micro wheel out towards 5 until the gun would not cock and then turned it back until the gun would cock. I then turned the front valve to where line 6 would be if there was one....I started shooting with the above settings, I was getting about 940fps....I started turning down the macro until I seen a drop in the fps, then I set it back just before the drop in fps, I shot more with turning the micro down until I seen a drop in fps. and set it back to just before the drop in fps., then I started shooting for groups turning the front valve in about a half turn at a time until I seen the groups starting to tighten up then I started tuning the valve 1/8th of a turn at a time until I got it shooting one hole groups at 50 yards and left it there.....It's shooting now 905-910 and shoots one hole groups at 50 yards and will shoot 1/2' or less at a 100 yards with no wind. When I installed the 1st reg bypass, I tried 120 on the second reg but mine shot a lot better when I turned the second reg to 130 and dialed back with the front valve...after getting the macro and micro set I quit watching the chrono as I could see the groups tightening up with each turn of the front valve....the fps just happened to be what it was after I got it dialed in for the tightest group that I could get. I know every gun is going to be different but that's how I got mine dialed in....and I'm shooting the 33.95 MK2's.....

 

[7Green]

I think the op had it tuned already and his/her gun started randomly shooting inconsistent velocities. I could be wrong, but that is how I read it, hence why I said to check those orings.

 

[Airgun-hobbyist]

Since you cleaned the barrel well and also the regulator, and that is consistent in pressure, the problem could be in the "action" on the moving parts that seal and also start the air flowing. The velocity spread and POI changes indicate they are sticking until they get "warmed up" from use. I'd recommend taking the Impact apart, cleaning and lubing the moving parts that seal on any dynamic O-rings. (In the valve sealing O-rings and where they contact along the stem especially). We used Krytox 205 or 207 to lube the moving/sealing parts of the older Impacts with great success.

On the Original and Gen2 Impact's, there was a hard o-ring we would change out for a plastic washer on the hammer weight. (On the newer Generation Impact with the Power Plenum and updated internals, things are different with the valve stem configuration from what I understand, but still would seal similarly.) An immediate fluctuation in fps and poi would indicate that this o-ring/washer had failed. It was only a bump-stop type of o-ring, oftentimes changed to a plastic washer, and have the symptoms you describe. It would also leave debris in there that effected the spring and hammer movement.

 

[MikeAllen]

By orings in the barrel, I am referring to the transferport area and not physically in the liner. Figured I better specify.

Haven’t changed the two barrel o-rings on either side of the transfer port. Good suggestion - I’ll give that a try - thanks!

 

[rc4fun]

The c1 can cause problems if it's loose, also if the valve rod has to much lube it will result in inconsistent ES. Ditto with the hammer.

 

[MikeAllen]

Thanks - I reassembled everything with very light lubrication - Ballistol - and did use blue loctite on the c1. All per Ernest Rowe’s videos. Thanks again for your input!

 

[DBlue]

I think the op had it tuned already and his/her gun started randomly shooting inconsistent velocities. I could be wrong, but that is how I read it, hence why I said to check those orings.

I guess the point I failed to mention was that after I deleted the 1st reg on my rifle that the gun was still inconsistent until I turned up the 2cd reg to 130 and went through the tuning procedure again, plus the OP listed his settings as factory specs for that particular pellet...every rifle is going to be different ....hence the reason for posting the tuning procedure.....sorry for boring anyone.....

 

[MikeAllen]

I had problems with the 1st reg. on my new MK3 and I installed the Saber Tactical bypass also....I set the 2cd reg to 130, turned the macro wheel to 16 then turned the micro wheel out towards 5 until the gun would not cock and then turned it back until the gun would cock. I then turned the front valve to where line 6 would be if there was one....I started shooting with the above settings, I was getting about 940fps....I started turning down the macro until I seen a drop in the fps, then I set it back just before the drop in fps, I shot more with turning the micro down until I seen a drop in fps. and set it back to just before the drop in fps., then I started shooting for groups turning the front valve in about a half turn at a time until I seen the groups starting to tighten up then I started tuning the valve 1/8th of a turn at a time until I got it shooting one hole groups at 50 yards and left it there.....It's shooting now 905-910 and shoots one hole groups at 50 yards and will shoot 1/2' or less at a 100 yards with no wind. When I installed the 1st reg bypass, I tried 120 on the second reg but mine shot a lot better when I turned the second reg to 130 and dialed back with the front valve...after getting the macro and micro set I quit watching the chrono as I could see the groups tightening up with each turn of the front valve....the fps just happened to be what it was after I got it dialed in for the tightest group that I could get. I know every gun is going to be different but that's how I got mine dialed in....and I'm shooting the 33.95 MK2's.....

Hadn't thought about setting the second reg higher and doing a complete retune - good advice - I think I'll try it - thanks!

 

[MikeAllen]

Since you cleaned the barrel well and also the regulator, and that is consistent in pressure, the problem could be in the "action" on the moving parts that seal and also start the air flowing. The velocity spread and POI changes indicate they are sticking until they get "warmed up" from use. I'd recommend taking the Impact apart, cleaning and lubing the moving parts that seal on any dynamic O-rings. (In the valve sealing O-rings and where they contact along the stem especially). We used Krytox 205 or 207 to lube the moving/sealing parts of the older Impacts with great success.

On the Original and Gen2 Impact's, there was a hard o-ring we would change out for a plastic washer on the hammer weight. (On the newer Generation Impact with the Power Plenum and updated internals, things are different with the valve stem configuration from what I understand, but still would seal similarly.) An immediate fluctuation in fps and poi would indicate that this o-ring/washer had failed. It was only a bump-stop type of o-ring, oftentimes changed to a plastic washer, and have the symptoms you describe. It would also leave debris in there that effected the spring and hammer movement.

Thanks for the insights - I'll do a complete teardown as a last resort - think I'll try other things first - but good knowing your previous experience!

 

[HogKiller]

Haven’t changed the two barrel o-rings on either side of the transfer port. Good suggestion - I’ll give that a try - thanks!

You might want to make sure the transfer port is tight/snug to the barrel, I had one come a touch loose somehow your symptoms were the same as I had.

 

[MikeAllen]

You might want to make sure the transfer port is tight/snug to the barrel, I had one come a touch loose somehow your symptoms were the same as I had.

Another good suggestion - thanks, I’ll check that also!

 

[Yxudden]

Hi,

Did you get your problem solved?

 

[MikeAllen]

Hi,

Did you get your problem solved?

Well, sort of solved. Went through many suggested steps and things have improved but I still find that the gun doesn’t “settle in” until I’ve fired about a half of a magazine. One thing I did that helped but isn’t related to the gun itself was to reset my scope to its optical center. I think over time , although zeroed, it was too far from optical center. I also switched to FX no limit mounts.

 

[Airgunmann]

How did the plastic on the end of the hammer look or the rubber balls In the valve adjuster ?

 

[MikeAllen]

How did the plastic on the end of the hammer look or the rubber balls In the valve adjuster ?

All looked good as I recall - BUT - I wasn’t checking those specifically. If I take it apart again I’ll look at those areas. Thanks for the feedback.