Tuning Impact M3 700 mm sniper: very very low slug velocity.

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MajorSylvester

MajorSylvester

Member
Jun 2, 2021
42
6
France, France
I have an impact M3 .22 cal 700mm, Sniper Edition, heavy slug liner for high power shooting 34 gr slugs at 200m. It worked reasonably well and lauched the 34 grains @ 922 fps with p Reg 2 = 150, spring tension reading 4.7 and valve fully open: 1 turn after the 4th mark. I got .8 MOA accuracy at 50m and very low S/D= 1.5. I decided to get a bit more power and reach 1000fps with the 34 grain slug. And I bough the slug power kit. I made the mistake to install the whole kit ( the 2 spacers, new spring,the little rubber ball and the pin probe. THis was a total failure and the maximum velocity I could reach was 800 fps with very high S/D. I know, I know, the kit was designed for the former impact versions and the only component to be installed on the M3 is the pin probe; I disasembled the kit, removed the small ball, replaced the new spring with the original, removed the spacers but kept the pin probe. I used the same tune as before and.... The M3 still cannot sent the 34 grains above 800 fps still with very high S/D.

In a nutshell: vanilla M3 worked fine, I installed the power kit, it didn't work, I removed the kit and returned to the vanilla version but it still doesn't work. Any idea about what is going on? I've spend the last 24 hours watching all M3 videos on the web and my brain is melting down. Any help from a fresher or smarter brain will be highly appreciated. Pascal.


 
Maybe the C1 isn't adjusted correctly ? 

Should be 6 to 6.5 mm

Screenshot_20211226-162854_YouTube.1640557765.jpg

 
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If I was where you are I would check to see that my barrel was in the right position and not on the small port. Put that lighter valve spring, from the power kit, back in and the original stock M3 probe as well. The pin probe, from the power kit, never did me any favors as the gun ran just as fast with my ported stock stock probe.

Go through most of the hammer settings again as well as it is pretty easy to screw up the balance on the reg pressure and hammer spring. 

I am running my .30 Sniper at 135bar and pushing a 47.2 slug at over 960fps, with some spring left, so it's not likely you need the full 150bar either.
 
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As others have said:

Install the pin probe and 2x hammer spring weights/spacers from the slug power kit, but do not install the valve adjuster spring or rubber balls. Those are not needed on the M3 and will limit valve travel and muzzle energy. Verify your C1 protrusion after installing the hammer spring spacers.

If your M3 has a 4 line front valve adjuster housing, fully open is 1.5 turns beyond the 4th line. Make sure the valve adjuster is fully open for maximum power.

The stock or even a Huma high flow pellet probe will be a bit of a restriction and higher muzzle energies, and the pin probe will yield a bit more velocity at the same exact hammer and valve settings compared to the pellet probe (at least in .22 caliber, which I've tested both the Huma high flow pellet probe and a Nielsen pin probe back to back, the Nielsen provided about 15 more fps at the same hammer spring and valve setting.) However, the pin probe may not seat deep skirted pellets far enough into the barrel to clear the transfer port if you switch between pellets and slugs, so keep that in mind. The FX pin probe is rather fragile though, a Nielsen pin probe is also adjustable but much stronger. The Huma pin probe is also stronger and a better option than the factory FX pin probe IMO, but it's not adjustable.


 
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Is there supposed to be a ball in the valve adjuster on the M3 double check that one isn't stuck in there maybe I'm not sure on the M3
Click to expand...

No free floating rubber balls inside the valve adjuster spring on the M3 like there were on the earlier impacts. On the M3 the rubber balls to cushion the valve opening are captive inside the valve adjuster knob itself. Adding the balls from the slug power kit inside the valve spring (like for earlier Impacts) severely limits how far the valve can open and limits power on the M3.

Schematic of M3 adjuster knob, cushioning rubber balls are #45 & #46 and are captive inside the knob.

m3knob.1640575946.jpg





 
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Dear all, thanks for your advices, it’s good to know I’m not alone with 2000 $ tomato pick. Let me specify my problem again. My M3, .22 cal 700mm worked perfectly before I tried foolishly to install the Power slug kit and it failed miserably. Now I’m just trying to come back to the previous vanilla situation just keeping the pin probe. Here is where the rifle stands for now. I removed the small rubber ball, replaced the original valve spring, and left the slug pin probe after checking and double checking time and again the slug pushed by the pin probe do not interfere with the transfer probe and that the barrel is installed with the slug transfer port down. I tried shooting both with the 2 spacer installed and without: no difference, the velocity for a 34 grain slug is still very low in the 700/800 range P reg is 170b but I also try decreasing the reg pressure to 150 b, same results. And yes I also decrease the spring tension moving the macro wheel from 16 to 15 and below: the velocity just decrease with the wheel. Therefore it is not an issue of tuning. It seems more serious. Every time the valve adjuster knob was fully open.

2 remarks:

  1. the valve adjuster knob can be adjusted well after the 4 th line, in my rifle it is just limited by the shroud and iI can adjust it 3 and a half turns after the 4th line. Most people speak of a max adjustment 1 and a half turn after the 4th line. Can it be a problem?
  2. The C1 protrusion was measured originally at 6.34 mm, now it is 6.07 mm. Can such a minimal difference have an impact (no pun intended)?
    [/LIST=1]

 
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