FX Valve return, line 4 or 6

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hgatesm

Member
Oct 1, 2022
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Carthage,bTexas, USA
Hello, As you may have seen from my previous posts I am STRUGGLING to get ANY kind of decent accuracy with slugs.

I keep seeing posts, and videos everyone talking about "line 4" on their return valve, the return valve on my gun has 6 lines, which I read in the manual models do come with either 4 or 6,,, there is a huge FPS difference between line 4 and line 6 with everything else being the same.

I was hoping to get some thoughts and opinions on what I should even try, today the best groups that I was able to shoot, I was shooting 43g NSA around 855-860 fps on "line 4"

When I say best groups, I'm still over 2 inches at 30 yards. If anyone would be willing to help, I would greatly appreciate it!
 
valve is your last step to tune. First, up reg and hammer in tandem until you’re 3-5% above your target speed. Not sure what speed NSA 43gr like but I’d guess 950 is as good a starting point as anything. Valve on line 6, up reg and hammer in tandem until they shoot at 990. If you can they to that speed with your hammer/spring then you can’t get there with that setup. Once you know what reg pressure gives you 990fps as plateau, dial the hammer back until you’re at 955-960. Now start adjusting the valve in until your at 950ish.
 
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greenbeans said:
valve is your last step to tune. First, up reg and hammer in tandem until you’re 3-5% above your target speed. Not sure what speed NSA 43gr like but I’d guess 950 is as good a starting point as anything. Valve on line 6, up reg and hammer in tandem until they shoot at 990. If you can they to that speed with your hammer/spring then you can’t get there with that setup. Once you know what reg pressure gives you 990fps as plateau, dial the hammer back until you’re at 955-960. Now start adjusting the valve in until your at 950ish.
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So based off that information, do you think having the valve all the way open (6) maybe that is part of the inaccuracy because the valve is open to long and causing turbulence?
 
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hgatesm said:
So based off that information, do you think having the valve all the way open (6) maybe that is part of the inaccuracy because the valve is open to long and causing turbulence?
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Yes, could be. But a bad tune will likely be inaccurate for tons of reasons. Valve is more of an efficiency/consistency thing though…
 
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greenbeans said:
Yes, could be. But a bad tune will likely be inaccurate for tons of reasons. Valve is more of an efficiency/consistency thing though…
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Gotcha, making some sense.

Trying to get this darn gun to shoot accurately has humbled me infinitely more than what I thought was possible.

To answer your most recent reply, using the heavy 'slug' liner from FX


To kind of summarize,

1. Valve on 6
2. Adjust reg/hammer in tandem till 1k fps
3. turn down hammer to 960 ish
4. turn valve down to 950 ish
 
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hgatesm said:
Gotcha, making some sense.

Trying to get this darn gun to shoot accurately has humbled me infinitely more than what I thought was possible.

To answer your most recent reply, using the heavy 'slug' liner from FX


To kind of summarize,

1. Valve on 6
2. Adjust reg/hammer in tandem till 1k fps
3. turn down hammer to 960 ish
4. turn valve down to 950 ish
Click to expand...
Sounds like a plan. Only adjust reg 5bar at a time and take 5ish shots after each adjustment of reg and/or hammer, needs a couple to settle. In particular when you get closer to target speeds.
 
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greenbeans said:
Sounds like a plan. Only adjust reg 5bar at a time and take 5ish shots after each adjustment of reg and/or hammer, needs a couple to settle. In particular when you get closer to target speeds.
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What would you recommend for reg pressuer as a starting point? Watching Matt Dubber on YT, he's pushing like 170 bar on that reg. I have no idea so open for suggestions on that one as well
 
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hgatesm said:
I have a tungsten hammer here and ready to go, also have pin probe installed as well
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Pin probe is good, I’d try stock hammer first and only put the tungsten in if you can’t get there. The tungsten hammer makes for a fairly violent shot cycle so I’d only use it if I really need it (and that’s unlikely - you have a 700mm barrel and want to shot 43gr 0.30 slugs, that should work without tungsten hammer…).
 
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hgatesm said:
I have a tungsten hammer here and ready to go, also have pin probe installed as well
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There is a risk of damaging the valve rod and stop assembly if it is open too far (or closed too far) and you hit it too hard with a heavy hammer strike. I would not open it further than line 5 to start with, and avoid using the tungsten hammer all together. It is too heavy of a hit unless you are running super high reg settings.

Reg settings are the other issue. You cannot run a stock FX AMP reg too high without shortening its lifespan, or flat out busting it. This goes for the front reg as well. FX and Ernest Rowe have stated many times you do not want to go over 170Bar, and really 150-160Bar is the max working pressure setting. And I can tell you from personal experience that spec is accurate. We have blown a handful of regs pushing them too far. So if you set your front reg at 160Bar, that doesnt leave a lot of room for your rear reg to have a healthy pressure differential. If you really want to push your rifle to the max you will need a front reg delete kit, and probably upgrade your rear reg to a Huma High Pressure. They have a working range of 150-200Bar, I have one in my rifle and it has been awesome.

The factory 30Cal hammer weight is usually good enough for about 140-150Bar, and the tungsten hammer weight is really only good for at least ~160Bar. My good friend has a tungsten in his built Impact M3 and even at 155-160Bar it is still on the edge of being too much hammer. My Impact MK2 has a Huma hammer weight and spring, both of which are slightly heavier than factory and I have full control at 150Bar.

All that being said, I would not advise you go down this road and keep things mostly stock. If you cant get slugs to shoot ok at 900fps, pushing them to 1050fps is likely not going to show any improvement. And in 30Cal the older FX platforms are getting close to the performance limit anyway. I wouldnt beat my rifle up chasing the dragon. My old Wildcat with a standard 500m STX liner was pretty good at short range even at 860fps Nielsen 43g slugs. I didnt do a whole lot of testing with that setup but I know it shot better than 3"at 30yds. My guess is you have another issue, like tune balance or loose parts.
 
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hgatesm said:
Gotcha, making some sense.

Trying to get this darn gun to shoot accurately has humbled me infinitely more than what I thought was possible.

To answer your most recent reply, using the heavy 'slug' liner from FX


To kind of summarize,

1. Valve on 6
2. Adjust reg/hammer in tandem till 1k fps
3. turn down hammer to 960 ish
4. turn valve down to 950 ish
Click to expand...
Simple way to tune an Impact.
Start with the valve knob on the last line, in your case 6. Given the gun you are tuning, I would start with the reg on 130 bar. Now set the Macro wheel on a middle setting, then adjust the micro up until the gun won’t cock. Back the micro off a couple clicks at a time until the gun cocks then go a couple clicks lower.
Now shoot the gun and check velocity. Increase reg pressure until your velocity is about 5-7% over your target speed. As another poster mentioned, take at least 5 shots to allow the gun to settle. Once you are at the hogher velocity start working the micro back until you get a drop in speed. Keep coming down until the speed is 5 or so fps over your target. Now is the time to start using the valve knob. Adjust it in until you see a small speed drop. Once you detect the speed drop only turn the valve knob in a 1/8 or quarter turn at a time and test groups size.
This method eliminates the need to be adjusting the hammer as you scale up the reg.every reg adjustment will be the maximum velocity for that reg setting.
Be aware that you may have to try several slugs before you find one that works
 
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Thank you all for the information, I got out and shooting this evening with what little daylight that I had. Per the above posts, I swapped out the tungsten hammer for the stock fx hammer.

Slowly started working on setting reg and hammer settings till I maxed those to the point I was not getting any more speed,,, Keep in mind this is at the valve return on 5.

Surprise surprise, accuracy was actually pretty good! At least the best I have had out of any slugs thus far in all of my testing. The big kicker here, was only getting about 840-850 fps. When I tried to increase the valve return towards line 6, accuracy just exited stage left.


Any thoughts??
 
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hgatesm said:
Reg ended up sitting just shy of 150bar, micro is almost maxed out and macro is on line 14/16, I couldn't gain any more velocity past these settings without moving the valve return.
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Gotcha. And what was your speed with valve on line 6?

Anyway I would have thought 150bar will give you more with 43gr and a 700mm barrel. Did you make sure c3 is fully screwed on and tight when you swapped hammers? If it is, I’m starting to think that the tungsten hammer already smashed the rubber balls behind the valve adjuster…
 
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greenbeans said:
Gotcha. And what was your speed with valve on line 6?

Anyway I would have thought 150bar will give you more with 43gr and a 700mm barrel. Did you make sure c3 is fully screwed on and tight when you swapped hammers? If it is, I’m starting to think that the tungsten hammer already smashed the rubber balls behind the valve adjuster…
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I'm not sure what c3 is. If its the piece at the end of the valve rod, yes I am certain that it is tight. You also mentioned rubber balls,, the stock valve return I had didn't have any rubber balls. the new spring that I have in there at the moment came with 1 and it looked to be fine when I had everything apart.
 
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