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HELP with FX Impact .25 Cal Slugs

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WGSmithII

WGSmithII

Member
Aug 19, 2019
16
1
Connecticut, United States
Requesting help from anyone with good results shooting 36 grain Nielsen .25 cal slugs through an FX impact X (not Mk II) with a 700mm slug barrel.

I’ve been tinkering like crazy with reg pressure & hammer spring to try and get 850+ fps muzzle velocity, and I can’t find the right combination. I increase the Reg pressure over 130 bar and the velocity goes down. I start low and gradually increase the hammer spring tension, and I can’t get over 800 fps consistently shot after shot.

Can anyone suggest the ‘magic’ reg pressure, hammer spring tension, and valve-stop distance to get me started for accuracy tuning?

Note that my FX has been retro-fitted with a Huma regulator and Huma/Wika bottle and regulates gauges.

Thanks for the help.
 
Have you tried to see how fast you can shoot a 34gr JSB just as a base line? The NSA's that I've shot (33.5gr) I believe are about 20fps slower than my 34gr JSB's so I think you'll lose some velocity there anyway. You might bump it up to about 160bar, go to the high setting and then increase the tension on the HS adjustment screw a couple of full turns CW to make sure the HS adjuster is really at max. Maybe others will chime in but it's possible that's all the MKI is capable of. Hopefully not though. Just as a comparison I can bump 960 with the JSB 34gr at 150bar. Hopefully it's just an adjustment issue.

Jimmy
 
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Velocity dropping over 130 bar seems unusual, particularly if the hammer spring is adjusted for minimum free play with the power wheel at Max. Seems like the hammer is not striking with the normal amount of force in your rifle. It may be that the C3 bumper is badly chewed up and hanging things up in there, especially if you have the original urethane o-ring bumper-- that might account for a loss of 50 fps or so. I would start around 140 bar and leave the valve-stop adjuster backed out to 4 lines or all the way out. If velocity still improves while going down in reg pressure, might consider pulling the valve rod and inspecting everything in there per Ernest Rowe's videos. Might also be a good time to go to the later valve spring revision (if you have the old 3-spring arrangement).
 
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Just to be clear, when you say you've been messing with the hammer spring, are you talking about the power wheel or the pre load that you adjust with the allen key? If you adjust the hammer spring pre load with the allen key so that the wheel will barely turn, so it's maxed out, then open the valve adjuster all the way out past 4 bars, then turn your regulator up to say 150-160BAR, the velocity should go up considerably. If it doesn't, the reasons could be... gun just doesn't have the power for the 36.2 slugs, C3 bumper broken, valve rod bent, valve seat and rod are not fitting tightly, transfer port not aligned, valve rod O-ring cracked or worn, cracked valve seat, valve seat housing set screw is not on the flat surface of valve housing. That's all I can think of. What kind of velocity do you get with the 33.95 or 25.39 pellets and at what reg. setting? It would be good to have some kind of baseline like JKing said. The slugs will shoot quite a bit slower than a pellet of the same weight, plus the 36.2 are quite a bit heavier. Hope it helps, good luck!

Stoti
 
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Hello!!

I have the 700mm .25 slug liner. My bumper is showing 4 marks, but has had fine tune backing down to get good groups. Regulator is on 160 bar by its gauge. 

I first ordered 38.5 hp, 36 dimple, and I think 33.5 hp. Still having stock gun, stock bumper, and all, I can barely get the 38.5 to 800 fps. Then I ordered 29.5s, and they max at 940fps. I went all the way out with bumper knob, and began backing it down in very small increments, 3 shots each time at 50yds.

I get about .5" at 50 yards at that perfect setting, but it's over 50 yards where they shine, holding that speed. I regularly hit drink cans at 300 now. 

Hope this helps.

I'm gonna try the 26.5 dish base next. Got a box now, and in betting I can drive them 1000 fps. I will measure my valve bumper -to- receiver with calipers before I move it lol. 
 
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Hello old thread! Lol

Yes, I now have the power plenum, C3, and dual-hole transfer port. I am shooting the 29.5 HP's at 1,000 if I want now, but I am only at about 125 reg pressure. Of course bumper lines are meaningless somewhat now. Mine did not drop velocity until I screwed it in to the 2nd line showing, and it dropped quickly there. So I settled on 960 FPS, and worked down. That video where the guy talked about his results he got making the tiny tweaks on the bumper knob until he had the right harmonics moving thru. They can seem pretty hopeless grouping until you hit that magic spot.

You know.....I wondered if there were any way to measure those correct harmonics in these rifles when they fire, to simply let us know when we are near or in those spots! That'd be the sheez neez! Haha!
























































































































































 
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Hello,

I'm new to the forum and apologies for the poor form digging up an old thread but I'm essentially having the same issue as the OP did here.

I have a FX Impact M3 25 cal
700mm standard barrel set on the slug port side
Slug power kit installed with pin probe and Tungsten hammer weight

I'm trying to get >900 fps with H&N 36 gr slugs but I'm currently only at ~810 fps with the following settings; Reg. 1 = 170, Reg. 2 = 125, Macro = 10, Micro = 4.25, and valve = 10.6mm. I can't go any higher on the Macro/micro wheels as it won't cock due to the added hammer weight length, and going any lower results in a few fps drop. Increasing the valve adjuster has the biggest effect (10's of fps) but I'm already a couple of turns past the 4th line, so I'm weary about extending that any further. Increasing the Reg. 2 pressure to 130-140 results in a velocity drop (to ~775 fps)...why? Anything I'm obviously doing wrong here? The impact should be capable of the velocities I'm looking for for this grain weight slug. Any suggestions?

Thank you!
 
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WGSmithII said:
Requesting help from anyone with good results shooting 36 grain Nielsen .25 cal slugs through an FX impact X (not Mk II) with a 700mm slug barrel.

I’ve been tinkering like crazy with reg pressure & hammer spring to try and get 850+ fps muzzle velocity, and I can’t find the right combination. I increase the Reg pressure over 130 bar and the velocity goes down. I start low and gradually increase the hammer spring tension, and I can’t get over 800 fps consistently shot after shot.

Can anyone suggest the ‘magic’ reg pressure, hammer spring tension, and valve-stop distance to get me started for accuracy tuning?

Note that my FX has been retro-fitted with a Huma regulator and Huma/Wika bottle and regulates gauges.

Thanks for the help.
Click to expand...
If you can't open the reg over 130bar, it sounds to me like you need a heavier spring and/or hammer weight.
 
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ruiopal said:
Hello,

I'm new to the forum and apologies for the poor form digging up an old thread but I'm essentially having the same issue as the OP did here.

I have a FX Impact M3 25 cal
700mm standard barrel set on the slug port side
Slug power kit installed with pin probe and Tungsten hammer weight

I'm trying to get >900 fps with H&N 36 gr slugs but I'm currently only at ~810 fps with the following settings; Reg. 1 = 170, Reg. 2 = 125, Macro = 10, Micro = 4.25, and valve = 10.6mm. I can't go any higher on the Macro/micro wheels as it won't cock due to the added hammer weight length, and going any lower results in a few fps drop. Increasing the valve adjuster has the biggest effect (10's of fps) but I'm already a couple of turns past the 4th line, so I'm weary about extending that any further. Increasing the Reg. 2 pressure to 130-140 results in a velocity drop (to ~775 fps)...why? Anything I'm obviously doing wrong here? The impact should be capable of the velocities I'm looking for for this grain weight slug. Any suggestions?

Thank you!
Click to expand...
With the stock valve adjuster spring installed you can go past line 4. I'm around imaginary line 6. A huma hammer spring may help with opening the valve longer or more too. If you install the huma valve adjuster spring, then line 4 may be max. I find it easy to blow the tiny oring on the valve rod with it installed, so I use the stock one.
 
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Most guns are very picky about shooting slugs as far as weight, diameter and manufacturer are concerned. I don't know why you are stuck with this slug and are pushing this gun to the limits. I'll give you my experience FWIW. I have an Impact MK2 with a 600 mm barrel and Superior liner. I've got the reg set at 110 bar and shoot JSB 33.95 gr KO slugs at 920 fps. Accuracy is great at 100 yards and I'm sticking with it.
 
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ruiopal said:
Thanks, I have all these things installed...I'll try going further with the valve adjuster and try higher Reg2 pressure again (perhaps 150)
Click to expand...
My MK2 has the 700mm Heavy liner, Huma port, Huma slug probe, Huma middle hammer weight and stronger spring, weaker return spring, Huma reg set @150Bar and full M3 style power plenum/block kit. My hammer pre load adjuster isnt maxed out yet and I have a heavier weight I can still use but Im getting great velocities with Nielsens 34.9-38.5 grain. The 34.9 is going about 995-1010fps.
 
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jps2486 said:
Most guns are very picky about shooting slugs as far as weight, diameter and manufacturer are concerned. I don't know why you are stuck with this slug and are pushing this gun to the limits. I'll give you my experience FWIW. I have an Impact MK2 with a 600 mm barrel and Superior liner. I've got the reg set at 110 bar and shoot JSB 33.95 gr KO slugs at 920 fps. Accuracy is great at 100 yards and I'm sticking with it.
Click to expand...
^^^^This is solid advice^^^^

A lot of people get frustrated with FX’s and primarily the Impact line because they do not wholly understand the gun.
I would suggest that any new comer to the Impact to learn to tune it. Learn to understand the interaction between the hammer and plenum pressure. Understand how turning all those adjusting points affects the performance. Tweak it until there is nothing more to be had from the gun and if that is not enough then add the cool stuff.
I did that with a Maverick and decided I like my guns in a lot more relaxed state to shoot. A more pleasant shot cycle and easier to tune accuracy was what I found.
 
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Thanks for the advice everyone. Turns out I did just need to go farther on the valve stop adjuster (now at 12mm), which brought up another question. Is the rubber ball inside the valve spring necessary? I'm wondering if I remove that it would allow for more hammer travel and thus not have to have the valve adjuster unscrewed so much?

Anyways, I'm now getting ~930-950 fps with the H&N HP 36gr slugs with the follow settings:
Reg 1 = 165
Reg 2 = 130
Macro wheel = 10
Micro wheel = 3.5
Valve adjuster = 12mm (~Line 6)

Now on to dialing in accuracy!

Cheers
 
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ruiopal said:
Thanks for the advice everyone. Turns out I did just need to go farther on the valve stop adjuster (now at 12mm), which brought up another question. Is the rubber ball inside the valve spring necessary? I'm wondering if I remove that it would allow for more hammer travel and thus not have to have the valve adjuster unscrewed so much?

Anyways, I'm now getting ~930-950 fps with the H&N HP 36gr slugs with the follow settings:
Reg 1 = 165
Reg 2 = 130
Macro wheel = 10
Micro wheel = 3.5
Valve adjuster = 12mm (~Line 6)

Now on to dialing in accuracy!

Cheers
Click to expand...
I would leave the rubber balls. They act as a cushion, especially if you push the gun hard.

I use mine for hunting, so I run it pretty hard. I am also very confident with disassembling the gun as I have done it a million times testing various setups.
 
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