FX Tuning to the knee… or maybe not?!

[greenbeans]

So my impact (700mm M4 in .25) can only open the valve up to 135b or so with the stock hammer but I wanted to try some heavier slugs (38gr and maybe 40, so not heavy heavy but heavier) and put in the 7.5g huma hammer to see what that would get me. Hammer can easily open the valve at 150b with micro below 4 and I didn’t go higher so far since the slugs I had around are not doing too well (so far at least).

While I’m waiting for a few other slugs to try, I thought I give 33.9 AEA pellets a try at low hammer spring just to see whether there’s something to the theory of “high reg, tiny tap with a heavier hammer and super short dwell = nice shot cycle and efficiency”… and I gotta say… It is shooting them real nice between 875 and up to 935. At around 885, the rifle sounds like completely balanced, very smooth and crisp shot cycle, accurate as hell and relatively stable spread. Like 12ish ES and 2.5 SD. I didn’t count shots yet but based on how it sounds ita probably very efficient. I had it tethered though so don’t know yet how the spread will look like when I shoot it from 250 down to reg pressure.

Anyway, this is obviously nowhere near the knee. I was shooting the AEA 33.9 at 915 on the knee for a while with stock hammer (high flow probe and barrel on slug port same as now) and 120b on the reg… so this is probably at around 85-ish % of max speed (didn’t look for the plateau with the pellets at 150b but I’d guess it’s 1050 or so). But it kind of “feels” right?!

Made me wonder, are people running these type of tunes? If so, what are lessons learned and did you eventually go back to the knee? If so, why? Kind of tempted to leave it like that and hope that I find a slug it’ll like at the knee at current pressure/settings.

 

[Vetmx]

Shoot five shots at 165b then fill the gun to 250b and shoot five shots. Then you will have your answer.

 

[MushroomPsyche]

The gun will be very efficient with high reg pressure and very short dwell time. Some people and some guns are ok with this in terms of accuracy over some arbitrary distance for the type of shooting they do. In my case however, I didn't have good luck with it. I have the Taipan Veteran which is a gun that many people say is "very versatile" for how "easy" it is to tune by just changing the hammer spring tension. When I first got the gun, it was tuned too hot for the pellets I was shooting. I didn't know anything about tuning back then and going by most people's advice, I "tuned" the gun lower by backing off the hammer spring. My gun is a standby varmint rifle. Over the next few months, I kept missing shots that I consider very easy shots. I'm talking about completely missing a squirrel at 20 meters away. This is when I started looking into it. I was keeping a log and I saw a pattern that the vast majority of my misses were from the first shots taken of the day. Many of the subsequent shots that where taken later in the day where hitting their marks. This is when I started researching and came to find out that there is a thing as a "first shot low". That was when I started getting into tuning my guns.

 

[greenbeans]

Shoot five shots at 165b then fill the gun to 250b and shoot five shots. Then you will have your answer.

In terms of horrible spread?

 

[SilentSquirrel]

@greenbeans
If you are into experimenting a little, I'd be curious to learn where the knee occurs if you leave the reg at 120 and play with hammer spring adjustment.

If you happen to try that please update

Edward

 

[greenbeans]

The gun will be very efficient with high reg pressure and very short dwell time. Some people and some guns are ok with this in terms of accuracy over some arbitrary distance for the type of shooting they do. In my case however, I didn't have good luck with it. I have the Taipan Veteran which is a gun that many people say is "very versatile" for how "easy" it is to tune by just changing the hammer spring tension. When I first got the gun, it was tuned too hot for the pellets I was shooting. I didn't know anything about tuning back then and going by most people's advice, I "tuned" the gun lower by backing off the hammer spring. My gun is a standby varmint rifle. Over the next few months, I kept missing shots that I consider very easy shots. I'm talking about completely missing a squirrel at 20 meters away. This is when I started looking into it. I was keeping a log and I saw a pattern that the vast majority of my misses were from the first shots taken of the day. Many of the subsequent shots that where taken later in the day where hitting their marks. This is when I started researching and came to find out that there is a thing as a "first shot low". That was when I started getting into tuning my guns.

Well… it’s an impact… first slow shot it almost part of the deal anyway I have the modded plenum part to cure it but it’s not 100% gone even with that… kinda want to say that valve rod through the plenum is just doomed by design but my ghost suffers from it as well. Bless the Eastern Europeans I guess.

 

[GMANCO]

Say more about the plenum mod ... an Impact M4 is on my list.

 

[greenbeans]

@greenbeans
If you are into experimenting a little, I'd be curious to learn where the knee occurs if you leave the reg at 120 and play with hammer spring adjustment.

If you happen to try that please update

Edward

hmmm I think it was micro at around 3 3/4 but every gun is different… no way around a chrony

 

[greenbeans]

Say more about the plenum mod ... an Impact M4 is on my list.

Seems like FX changed the part themselves meanwhile but not sure how good their fix actually is. Anyway, @mubhaur makes a part that’s basically old style impact that seats the plenum orings properly and is the best shot to cure. There’s people out there that seem to copy his design on eBay…

 

[6gun]

Well… it’s an impact… first slow shot it almost part of the deal anyway I have the modded plenum part to cure it but it’s not 100% gone even with that… kinda want to say that valve rod through the plenum is just doomed by design but my ghost suffers from it as well. Bless the Eastern Europeans I guess.

When I changed both my regs to huma I got 1st shot to be in the pocket with following shots. I'm mostly a first shot has to count sort of hunting situation guy. Even if pesting. I'm glad I got that reputation of the impact out of my 700mm m3.

Edit. I also swapped the plenum when I did the power block(mines early production) but I didn't see anything different so I didn't mic it. I did have a bone to pick with the block so I went measuring what I could to see if it's a safety fix or performance. It's kind of the former so you can chase the latter Imho.

 

[Vetmx]

The gun will be very efficient with high reg pressure and very short dwell time. Some people and some guns are ok with this in terms of accuracy over some arbitrary distance for the type of shooting they do. In my case however, I didn't have good luck with it. I have the Taipan Veteran which is a gun that many people say is "very versatile" for how "easy" it is to tune by just changing the hammer spring tension. When I first got the gun, it was tuned too hot for the pellets I was shooting. I didn't know anything about tuning back then and going by most people's advice, I "tuned" the gun lower by backing off the hammer spring. My gun is a standby varmint rifle. Over the next few months, I kept missing shots that I consider very easy shots. I'm talking about completely missing a squirrel at 20 meters away. This is when I started looking into it. I was keeping a log and I saw a pattern that the vast majority of my misses were from the first shots taken of the day. Many of the subsequent shots that where taken later in the day where hitting their marks. This is when I started researching and came to find out that there is a thing as a "first shot low". That was when I started getting into tuning my guns.

And this is why the DonnyFL “speed dialer” for the Taipan has a horribly misleading name. In all guns, your speed dialer is your reg. I’ve seen for many years where guys do use their hammer spring as a speed control. I’ve tried, I’m picky, and I know what my guns are capable of. This method sucks. If you have even the slightest reg creep or temp swings, you’re done for not just the first shot, but maybe a couple more. The other issue is most PCP’s, not all, have a zone in their fill range where they perform best. Being at the knee lets you maximize most of it. Dumbing down a gun with the hammer strike can make it worse. But if you’re getting way more shots per fill, it may or may not balance out. But that’s a whole new topic and depends on the gun and what a guy is asking out of it.

 

[6gun]

And this is why the DonnyFL “speed dialer” for the Taipan has a horribly misleading name. In all guns, your speed dialer is your reg. I’ve seen for many years where guys do use their hammer spring as a speed control. I’ve tried, I’m picky, and I know what my guns are capable of. This method sucks. If you have even the slightest reg creep or temp swings, you’re done for not just the first shot, but maybe a couple more. The other issue is most PCP’s, not all, have a zone in their fill range where they perform best. Being at the knee lets you maximize most of it. Dumbing down a gun with the hammer strike can make it worse. But if you’re getting way more shots per fill, it may or may not balance out. But that’s a whole new topic and depends on the gun and what a guy is asking out of it.

Mines happiest with a 240 bar fill it will do a full fill but the groups really stay together 190-240

 

[greenbeans]

And this is why the DonnyFL “speed dialer” for the Taipan has a horribly misleading name. In all guns, your speed dialer is your reg. I’ve seen for many years where guys do use their hammer spring as a speed control. I’ve tried, I’m picky, and I know what my guns are capable of. This method sucks. If you have even the slightest reg creep or temp swings, you’re done for not just the first shot, but maybe a couple more. The other issue is most PCP’s, not all, have a zone in their fill range where they perform best. Being at the knee lets you maximize most of it. Dumbing down a gun with the hammer strike can make it worse. But if you’re getting way more shots per fill, it may or may not balance out. But that’s a whole new topic and depends on the gun and what a guy is asking out of it.

I kind of suspected it to be too good to be true ( and, therefore, not a thing a lot of people talk about…). Will try and shoot it down from 250 anyway just to see how it does, but back to the knee it is I guess…

 

[JaceSpace1369]

So my impact (700mm M4 in .25) can only open the valve up to 135b or so with the stock hammer but I wanted to try some heavier slugs (38gr and maybe 40, so not heavy heavy but heavier) and put in the 7.5g huma hammer to see what that would get me. Hammer can easily open the valve at 150b with micro below 4 and I didn’t go higher so far since the slugs I had around are not doing too well (so far at least).

While I’m waiting for a few other slugs to try, I thought I give 33.9 AEA pellets a try at low hammer spring just to see whether there’s something to the theory of “high reg, tiny tap with a heavier hammer and super short dwell = nice shot cycle and efficiency”… and I gotta say… It is shooting them real nice between 875 and up to 935. At around 885, the rifle sounds like completely balanced, very smooth and crisp shot cycle, accurate as hell and relatively stable spread. Like 12ish ES and 2.5 SD. I didn’t count shots yet but based on how it sounds ita probably very efficient. I had it tethered though so don’t know yet how the spread will look like when I shoot it from 250 down to reg pressure.

Anyway, this is obviously nowhere near the knee. I was shooting the AEA 33.9 at 915 on the knee for a while with stock hammer (high flow probe and barrel on slug port same as now) and 120b on the reg… so this is probably at around 85-ish % of max speed (didn’t look for the plateau with the pellets at 150b but I’d guess it’s 1050 or so). But it kind of “feels” right?!

Made me wonder, are people running these type of tunes? If so, what are lessons learned and did you eventually go back to the knee? If so, why? Kind of tempted to leave it like that and hope that I find a slug it’ll like at the knee at current pressure/settings.

@RoosterCogburn maybe you can add to this since you've messed with yours when it was a .25 quiet a bit. Not sure that there is much of an internal difference between the M4 and M3

 

[RoosterCogburn]

@RoosterCogburn maybe you can add to this since you've messed with yours when it was a .25 quiet a bit. Not sure that there is much of an internal difference between the M4 and M3

Im not very experienced compared some of the others on here. But,
I found poor efficiency at 120-135 trying to move 36 gr takeaim/hp2/jav 250 g2s at 920-925. Got 40grs up to 895 but had to refill every magazine.

This involved fairly high end of the hammer spring 'micro' and a max on.the mk2pp wheel. About 3.2-2.5 on the wheel.
I would degas and detune and work up to the max. Always starting at 125b. 0 on hs screw, and 5 on the wheel.

34s at 955
36 @920-925
40@ mainly at 891-895. Hitting 898 once. Would usually be the 2nd shot after an increase on hammer spring.


At lower pressures starting at 4 lines on the VA id find a raise in velocity once the valve was at a proper dwell time. I realize this is the "knee" for that given pressure/hammer combo and the real consistency would be found soon after. This was done with the 500mm


Ive since changed to
.22/700 left all.springs stock and added 13.2 hammer. That's it. I polished the valve springs. Micro tuning the valve and micro over the chrono can minimize the first shot low.

Right now at 135b~ 4 on the wheel, maybe 3 turns in on the hammer spring screw, about 2.8 valve adjuster. Shooting 26gr take aim .2175 @ 956 avg. I get A LOT of duplicate results and my extreme has not exceeded 11 fps in a long time. Average shot to shot is well under 2 fps. My "low shot" is typically 946-949 with all following at a very stable and consistent velocity.

I am probably going to increase to. 145 and maintain velocity. On MAX this gun as tuned shooting 27.5nsa .217 at 990 thr 26s at ~1020.. I mark what I judge optimum spots on the valve with horizontal, vertical, and diagonal lines for 4/5/max.

Highest ive gone.with .22 is 34s at 960. Didnt want to go further, but could have.

 

[RoosterCogburn]

Mines happiest with a 240 bar fill it will do a full fill but the groups really stay together 190-240

220-165 is my "güdkreem g00nz0n3"

 

[Vetmx]

All three of my guns are the same gun at 250b down to 160b.

Edit: Just shot a mouse at 130 yards earlier and posted the video. After typing this I walked in to check my tank pressure. It’s 160b. Second reg is set at 155b.

 

[mubhaur]

Seems like FX changed the part themselves meanwhile but not sure how good their fix actually is. Anyway, @mubhaur makes a part that’s basically old style impact that seats the plenum orings properly and is the best shot to cure. There’s people out there that seem to copy his design on eBay…

I don't mind people copying my part but they should at least mention on the website that it was initially introduced by Umair Bhaur. Courtesy to him. We should have this much ethics at least.

 

[JaceSpace1369]

Im not very experienced compared some of the others on here. But,
I found poor efficiency at 120-135 trying to move 36 gr takeaim/hp2/jav 250 g2s at 920-925. Got 40grs up to 895 but had to refill every magazine.

This involved fairly high end of the hammer spring 'micro' and a max on.the mk2pp wheel. About 3.2-2.5 on the wheel.
I would degas and detune and work up to the max. Always starting at 125b. 0 on hs screw, and 5 on the wheel.

34s at 955
36 @920-925
40@ mainly at 891-895. Hitting 898 once. Would usually be the 2nd shot after an increase on hammer spring.


At lower pressures starting at 4 lines on the VA id find a raise in velocity once the valve was at a proper dwell time. I realize this is the "knee" for that given pressure/hammer combo and the real consistency would be found soon after. This was done with the 500mm


Ive since changed to
.22/700 left all.springs stock and added 13.2 hammer. That's it. I polished the valve springs. Micro tuning the valve and micro over the chrono can minimize the first shot low.

Right now at 135b~ 4 on the wheel, maybe 3 turns in on the hammer spring screw, about 2.8 valve adjuster. Shooting 26gr take aim .2175 @ 956 avg. I get A LOT of duplicate results and my extreme has not exceeded 11 fps in a long time. Average shot to shot is well under 2 fps. My "low shot" is typically 946-949 with all following at a very stable and consistent velocity.

I am probably going to increase to. 145 and maintain velocity. On MAX this gun as tuned shooting 27.5nsa .217 at 990 thr 26s at ~1020.. I mark what I judge optimum spots on the valve with horizontal, vertical, and diagonal lines for 4/5/max.

Highest ive gone.with .22 is 34s at 960. Didnt want to go further, but could have.

Given how often you tune and how well your tunes come out to be, your input is as good as anyone with more experience. I'd put my input but it's been years and I've never ran with a .25

I did tune my coworkers m3 .25 600mm, 1st reg delete, rear reg at 145b but idk the rest of the tune. It's shooting 40gr at 888fps and shooting about 33 really good and consistent shots

 

[RoosterCogburn]

Given how often you tune and how well your tunes come out to be, your input is as good as anyone with more experience. I'd put my input but it's been years and I've never ran with a .25

I did tune my coworkers m3 .25 600mm, 1st reg delete, rear reg at 145b but idk the rest of the tune. It's shooting 40gr at 888fps and shooting about 33 really good and consistent shots

I appreciate it. I think my obsessive and meticulous perfectionist nature coupled with the inherent neuroticism of being a sperg plays into this. A good 60% of my ammo use is solely being shot into a catch box over the chrono trying to find that perfect setting or as close to it as possible. Noise, Air usage, velocity, spread, and grouping all have to be near perfect in order for me to be able to stop and call it tuned. Hours and hundreds of shots are taken every single time I change something. then of course letting it sit for a day to see if things settled agreeably, and god help me if i see 1 spike or dip after the first shot gets things moving. I expect, with the exception of the first shot or two EVERY single following shot to be within 1.5-2fps over or under of the one preceding it. Not exactly reasonable or necesarry, but, something inside me screams when my nice flat line gets a kink.