Tuning Impact M3 Adjustment

When we perform a speed adjustment for a certain projectile we always strive to be on the top of the bell curve maximizing the hammer spring for an established regulator pressure. And then, reduce it by 3%-5% using the front valve adjuster knob. In doing so we have the optimal speed, less spread and max autonomy. If the projectiles don't group well, we change the regulator pressure by 5% up or down and repeat the above process. This is what I have been doing over the years on my previous Impacts.

I am having difficulty understanding the M3 adjustment. It seems it doesn't follow the same rationale. At least when I watch the FX Masterclass videos and other shooters. Would you please help me to understand the M3 speed adjustment process? 

Thank you in advance.
 
The method you described still works with the M3 and certainly works well for pellets, although my preference is to set the hammer spring slightly under the peak velocity plateau for a given regulator pressure and then fine tune down just a bit with the valve adjustment if tuning following your method.

The other line of thinking for tuning (especially with slugs, but for pellets too) is to run the valve wide open, use a higher reg pressure than needed for your desired velocity, and dial in the velocity by reducing the hammer spring which will end up well back of the peak velocity for that regulator pressure. The idea behind this tuning method is that using a higher than needed reg pressure results in a very short valve opening time for a short pulse of higher pressure air for better efficiency. The higher than needed reg pressure also helps to close the valve quickly.

One question when tuning this way (higher reg pressure with reduced hammer spring) is shot count compared to a tune as you described, where the regulator is set just above your desired velocity. Some say the higher reg pressure with reduced hammer spring is more efficient because of shorter valve opening times which results in better air efficiency, where others say the method you described will get more shots per fill since the regulator pressure is lower with that method and from a full fill you have a wider working range before the rifle falls off the regulator.

I recently tuned my new M3 for slugs, and while 120 bar on the regulator was enough to plateau 15fps above my desired velocity, the rifle was much more accurate with the regulator increased to 135 bar and the velocity set 45fps behind the peak velocity using only the hammer spring tension and leaving the valve wide open.

Next test I need to do is compare shot count and accuracy at 135 bar on the regulator using 2 methods to reach the target velocity: 1 leaving the valve wide open and the velocity dialed back using the hammer spring as I have it now, and 2 setting the hammer spring for 5-8 fps under the peak velocity with the valve fully opened and then reducing the velocity to the desired velocity only by closing the valve. Method #1 seems to be the most recommended for slug tunes, but I want to see what effect method #2 has on accuracy, velocity spread, and shot count.

EDIT:

Just got back in from trying the tune both ways with my slug tuned M3 (max valve / reduced hammer spring tune vs max hammer spring / reduced valve tune.)

With the valve fully opened to about 4.5 lines and the regulator at 135 bar, the peak velocity was 1005 fps.

First I tried my current method of tuning which was leaving the valve at about 4.5 lines (full open) and dialing the HST back to the max accuracy velocity of 960 fps. Then I did a shot count test from 200-150 bar. Shot count was 35, extreme spread was 9fps, SD was 2.5fps.

Next, with the valve still at 4.5 turns full open I adjusted the hammer spring for 1000fps (just under the peak velocity) and reduced the velocity to 960 fps using only the valve adjuster. Shot count from 200-150 bar was 34 shots, extreme spread was 13 fps, SD was 3.4 fps.

While the numbers (shot count, ES, SD) were close, the SD/ES was marginally better with the max valve / reduced hammer spring setup. The accuracy was also better with the max valve / reduced hammer spring tune. Also, the sound of the rifle seemed to be identical with both setups, which makes sense as air use / shot count was pretty much identical between the two setups.

I suppose it all boils down to which tuning method produces better results at the target. The Impact gives you multiple ways to reach the same goal, which is either a good thing or a bad thing depending on how you look at it. As evidenced by my test tonight, 2 different tuning schemes can produce nearly identical shot count / velocity / ES / SD numbers but have a noticeable difference in group size... which means it takes more air, ammo, and time to test all combinations to find out what's the most accurate.
 
Great points! You guys get it! The interesting part I have experienced with each plenum size change was also that peak reg preferences went down as plenum size increased, also, take note of the massive valve spring resistance increase? With 3/8” of spring preload upon disassembly, what is full open? I’m not sure yet? But working it? I am also seeing a 5 shot minimum after reg adjustment to settle? 👍🏻


thanks,
 
kiba



Just got back in from trying the tune both ways with my slug tuned M3 (max valve / reduced hammer spring tune vs max hammer spring / reduced valve tune.)

This was one of the few tests I've done so far, and my results mirror yours. 



Impact M3 .30 700mm. 

Reg 110bar (max achievable velocity ~945fps)

JSB 44.75gr pellets

tuned for 880fps (7% down from max)



Shooting at 100yards, accuracy with valve wide open and hammer spring reduced was more accurate than reducing velocity using the valve. Not a huge difference, but noticeable at 100yards when comparing 3 10-shot groups done each way. If you were shooting at 50yards it would probably be hard to tell.



Glad it turned out this way because the valve doesn't have indexing and is hard to work with if you want to be able to return to a tune. It's probably one of the few things that FX could improve (along with the whole barrel liner o-ring thing).



Many more things to try. Next will probably be to compare 100bar to 110bar tunes for pellets. Gun seemed to like that 110bar setting for both sound and accuracy but need to actually dedicate the time to confirm. I also think I'm getting more shots from a 250bar fill but need to confirm that as well. 
 
  • Like
Reactions: iobrien1


Glad it turned out this way because the valve doesn't have indexing and is hard to work with if you want to be able to return to a tune. It's probably one of the few things that FX could improve (along with the whole barrel liner o-ring thing).




Agreed, if FX engraved graduated markings on the valve adjuster housing and knob like a micrometer it would be easy to set and repeat the valve between different settings. Could be done with laser engraving for probably not a lot of added cost on their end. 

I'm probably going to put a little dab of shoe goo on my valve adjuster where the knob meets the housing to hold it in place since there's no easy way to tell if it was moved a little bit. It dries clear so it won't be unsightly, holds well, and is easy to peel off cleanly in the future if you need to disassemble or adjust the valve. An alignment stripe over the knob and housing with a silver sharpie or paint pen would work too as a visual indicator, but won't keep the knob from being adjusted accidentally.
 
  • Like
Reactions: iobrien1
Agreed, if FX engraved graduated markings on the valve adjuster housing and knob like a micrometer it would be easy to set and repeat the valve between different settings. Could be done with laser engraving for probably not a lot of added cost on their end. 
I'm probably going to put a little dab of shoe goo on my valve adjuster where the knob meets the housing to hold it in place since there's no easy way to tell if it was moved a little bit. It dries clear so it won't be unsightly, holds well, and is easy to peel off cleanly in the future if you need to disassemble or adjust the valve. An alignment stripe over the knob and housing with a silver sharpie or paint pen would work too as a visual indicator, but won't keep the knob from being adjusted accidentally.

The manual states 1.5 turns out from 4th line is supposed to be full open, so I did just that, then I took a silver sharpie and colored in one of the deep grooves in the valve adjuster knob facing exactly 90deg to the right. Sharpie can rub off, but because it is in the groove it doesn't get touched. Easy to see if it has moved and easy to return to where it should be. When I indexed my barrel liner, sharpie and even paint didn't stick well enough so I had to use a dremel with carbide burr to make tiny dots.

I've briefly considered various options in my head for DIY fine indexing of the valve adjuster, but haven't come up with any good solutions yet. The limited space to work in makes it challenging. Like you said, real solution would be engraving done by FX. Hopefully they would have even number of turns line up exactly with lines/marks. I have found that clicks on the hammer spring micro adjuster don't exactly line up with marks like I would hope (meaning 10 clicks of the micro adjuster should exactly match the 0.25 marks on the gun, but they don't). It seems off by a click or two.
 
I have another question . Using the valve at 4.5 do you notice that the macro can be shooting at the same power level for a few of the values ? For instance 16- 890 15-890 14-890 13-890 and it may take till 7 on the macro to speeds decrease.. Am I doing something wrong? 


this is .177. Reg is 60.



Sounds like you have way too much hammer spring for a 60 bar regulator setting and are tuned will beyond the velocity plateau. With the regulator at only 60 bar it isn't going to take much hammer spring tension to reach the velocity plateau or go beyond it (which just wastes air.)

I would set the macro to 1 and the micro to about 1.25, then dial the macro up 1 at a time until you find the velocity plateau. If you don't find it by the time you get to 16 on the macro, leave the macro at 16 and start dialing up the micro 3-4 clicks at a time until you find the peak velocity. Then dial the micro back down about 5% under the peak.

Chances are with only 60 bar on the regulator pressure you'll find the velocity peak well before getting to 16 on the macro wheel.

You could close down the valve adjustment some as the low regulator pressure won't really assist much in limiting the valve opening or helping it close quickly as a higher regulator pressure would.
 
This was one of the few tests I've done so far, and my results mirror yours.



Impact M3 .30 700mm.

Reg 110bar (max achievable velocity ~945fps)

JSB 44.75gr pellets

tuned for 880fps (7% down from max)



Shooting at 100yards, accuracy with valve wide open and hammer spring reduced was more accurate than reducing velocity using the valve. Not a huge difference, but noticeable at 100yards when comparing 3 10-shot groups done each way. If you were shooting at 50yards it would probably be hard to tell.



Glad it turned out this way because the valve doesn't have indexing and is hard to work with if you want to be able to return to a tune. It's probably one of the few things that FX could improve (along with the whole barrel liner o-ring thing).



Many more things to try. Next will probably be to compare 100bar to 110bar tunes for pellets. Gun seemed to like that 110bar setting for both sound and accuracy but need to actually dedicate the time to confirm. I also think I'm getting more shots from a 250bar fill but need to confirm that as well.
Great reporting , much appreciated
 
The method you described still works with the M3 and certainly works well for pellets, although my preference is to set the hammer spring slightly under the peak velocity plateau for a given regulator pressure and then fine tune down just a bit with the valve adjustment if tuning following your method.

The other line of thinking for tuning (especially with slugs, but for pellets too) is to run the valve wide open, use a higher reg pressure than needed for your desired velocity, and dial in the velocity by reducing the hammer spring which will end up well back of the peak velocity for that regulator pressure. The idea behind this tuning method is that using a higher than needed reg pressure results in a very short valve opening time for a short pulse of higher pressure air for better efficiency. The higher than needed reg pressure also helps to close the valve quickly.

One question when tuning this way (higher reg pressure with reduced hammer spring) is shot count compared to a tune as you described, where the regulator is set just above your desired velocity. Some say the higher reg pressure with reduced hammer spring is more efficient because of shorter valve opening times which results in better air efficiency, where others say the method you described will get more shots per fill since the regulator pressure is lower with that method and from a full fill you have a wider working range before the rifle falls off the regulator.

I recently tuned my new M3 for slugs, and while 120 bar on the regulator was enough to plateau 15fps above my desired velocity, the rifle was much more accurate with the regulator increased to 135 bar and the velocity set 45fps behind the peak velocity using only the hammer spring tension and leaving the valve wide open.

Next test I need to do is compare shot count and accuracy at 135 bar on the regulator using 2 methods to reach the target velocity: 1 leaving the valve wide open and the velocity dialed back using the hammer spring as I have it now, and 2 setting the hammer spring for 5-8 fps under the peak velocity with the valve fully opened and then reducing the velocity to the desired velocity only by closing the valve. Method #1 seems to be the most recommended for slug tunes, but I want to see what effect method #2 has on accuracy, velocity spread, and shot count.

EDIT:

Just got back in from trying the tune both ways with my slug tuned M3 (max valve / reduced hammer spring tune vs max hammer spring / reduced valve tune.)

With the valve fully opened to about 4.5 lines and the regulator at 135 bar, the peak velocity was 1005 fps.

First I tried my current method of tuning which was leaving the valve at about 4.5 lines (full open) and dialing the HST back to the max accuracy velocity of 960 fps. Then I did a shot count test from 200-150 bar. Shot count was 35, extreme spread was 9fps, SD was 2.5fps.

Next, with the valve still at 4.5 turns full open I adjusted the hammer spring for 1000fps (just under the peak velocity) and reduced the velocity to 960 fps using only the valve adjuster. Shot count from 200-150 bar was 34 shots, extreme spread was 13 fps, SD was 3.4 fps.

While the numbers (shot count, ES, SD) were close, the SD/ES was marginally better with the max valve / reduced hammer spring setup. The accuracy was also better with the max valve / reduced hammer spring tune. Also, the sound of the rifle seemed to be identical with both setups, which makes sense as air use / shot count was pretty much identical between the two setups.

I suppose it all boils down to which tuning method produces better results at the target. The Impact gives you multiple ways to reach the same goal, which is either a good thing or a bad thing depending on how you look at it. As evidenced by my test tonight, 2 different tuning schemes can produce nearly identical shot count / velocity / ES / SD numbers but have a noticeable difference in group size... which means it takes more air, ammo, and time to test all combinations to find out what's the most accurate.
Most educational, detailed post I’ve read so far. Awesome info and thank you!!