Tuning FX Impact Tuning - 2 schools of thought

[Corvid_hunter]

I watched Matt Dubber's tuning video with regard to high reg pressures (and higher hammer spring). Many other videos also say to start with the hammer spring maxed out. I seem to remember watching Steve's (AEAC?) where he set the hammer spring so the Power Wheel barely moved between MIN and #1. This uses a lower reg pressure if I'm not mistaken. Steve ended up with a high shot count and a SD of around 3-4fps (if I remember right). I'm going to be tuning for 35gr slugs (MKII 700mm .25cal with Huma V2 TP and probe) with a target speed of 950-975fps. My current 100bar tune is giving me close to 900fps with the 35gr slugs. What are the pros and cons of going up 10-20 bar and hitting my target speed vs going to 150-165bar and tuning from there?

 

[corny]

The idea of starting at max HS is to ensure max velocity at said reg pressure. 


like say you want to tune to 900 FPS. U set HS to max and start backing out or increasing reg till u hit roughly 930-960 fps.

u then back out the HS till u get 900fps. This should balance the valve and hammer. U will hear the gun quieting down as u near the sweet spot. 

this is usually done with valve wide open, u can then close the valve till u see it make an obvious decrease in the FPS. 

 

[corny]

running higher reg pressures than necessary gave we a wider ES. Also a more violent shot. As more HS is needed to open the valve 

 

[Corvid_hunter]

The idea of starting at max HS is to ensure max velocity at said reg pressure. 


like say you want to tune to 900 FPS. U set HS to max and start backing out or increasing reg till u hit roughly 930-960 fps.

u then back out the HS till u get 900fps. This should balance the valve and hammer. U will hear the gun quieting down as u near the sweet spot. 

this is usually done with valve wide open, u can then close the valve till u see it make an obvious decrease in the FPS. 

This is a very simple, straight forward way of describing how to tune an Impact. Thanks.

 

[Saltlake58]

Some of the videos came out before the Power Plenum, so tuning seems to be a bit different now. 68 Whiskey did a video on tuning that included the Power Plenum

The older guns (I have a Gen 1 and a MKII) just didn't have the ability to shoot hard and fast with heavier projectiles. FX started improving the plumbing in the gun with the Impact X and into the MKII's. The method shown here gets you a nice balance without the violence of the super high reg pressures.

https://www.youtube.com/watch?v=KDvuMwjwk9M

As an example, I like to shoot my Gen 1 with 34 grain pellets. Before installing the PP, the regulator was set at 145 bar shooting on power lever MAX to get 850 fps. After the PP installation, about 110 bar power level 4 for the same performance. Massive improvement.

The newer models have a much greater power curve, so have a look at the video before settling on a high regulator pressure.

 

[DShepard]

The tune on my gun (in that video) was shooting 33.95s @960. 145 bar, maxed hammer spring. After shooting it at home, there was a wide spread in velocity. A few small adjustments on the valve spring had it down to about 2 fps spread. I can shoot 3 mags, or 84 shots, without losing speed with a 580cc bottle.

 

[Corvid_hunter]

Double post.

 

[Corvid_hunter]

Can't complain about that tune or those results.

 

[Vetmx]

I’ve seen quite a few ways to tune an Impact. I’m not going to go into details about how I do it but I will give you 2 tips. First, it doesn’t take a genius to get a pellet to shoot good out of a Impact, even with a semi jacked up tune. So a pellet tune is not a slug tune. The second thing is about how sensitive the FX platform is concerning harmonics. If you can’t get your pellet tune to maintain a very tight velocity spread from max fill all the way down to when you refill the gun, you will never get it to shoot a slug with the consistency that the gun does it with pellets. Pellets are way more forgiving of an oddball tune than a slug is.

 

[tor47]

The reason Matt Dubber mentioned high pressure can be benefitial with slugs is that, slugs doeas not have skirts like pellets. Some have what looks like small skirts, like JSB knockouts, and some have a cup. So higher pressure can make the slug expand a litle on the backside, and engage rifling better. It probably depends on the type of slugs. My .22 knockouts doeas not require high regpressure with a 700mm barrel. I use the standard superior liner on my gun, and they shoot fine with 110 bar. Do not know if the slugliner will be different. You probably has to try both scenarious if you want to find out what is best for you gun. 

 

[Rallyshark]

Personally, I tend to err towards a higher reg set point, or the common methods for tuning a regulated rifle. That is, I usually shoot 3-5% below the plateau, or max speed the gun can shoot at a given reg setting. That's the best combo of efficiency and power for any given regulator setting, imo. So If I want a 950 fps tune, I'll usually have the reg set where the max speed is 975-1000 fps for that reg setting, then I'll back the HS down to get the 950 fps I want. The slightly higher reg setting makes the valve close faster and is more air efficient. You also get less turbulence on the muzzle end and a quieter gun. This results in a calmer, tighter shot cycle.

Another way of putting it. I'll often tune my Maverick to where it hits it's absolute max speed on PW7, then I do most of my shooting at PW6. To get the best ES on a gun without valve adjustment you have to tune closer to the plateau, but with the impact you can clean that ES up with the valve adjustment in many cases. I think people do tend to get too caught up with the ES or SD. I'm not going to worry, if my ES is 15 fps, and I'm certainly not going to drive myself crazy trying to get that ES under 10 fps. Don't get me wrong, if I was shooting for money, then I'd care a bit more, but 99.5% of us will never see that difference on target, imo

 

[Bigragu]

Personally, I tend to err towards a higher reg set point, or the common methods for tuning a regulated rifle. That is, I usually shoot 3-5% below the plateau, or max speed the gun can shoot at a given reg setting. That's the best combo of efficiency and power for any given regulator setting, imo. So If I want a 950 fps tune, I'll usually have the reg set where the max speed is 975-1000 fps for that reg setting, then I'll back the HS down to get the 950 fps I want. The slightly higher reg setting makes the valve close faster and is more air efficient. You also get less turbulence on the muzzle end and a quieter gun. This results in a calmer, tighter shot cycle.

Another way of putting it. I'll often tune my Maverick to where it hits it's absolute max speed on PW7, then I do most of my shooting at PW6. To get the best ES on a gun without valve adjustment you have to tune closer to the plateau, but with the impact you can clean that ES up with the valve adjustment in many cases. I think people do tend to get too caught up with the ES or SD. I'm not going to worry, if my ES is 15 fps, and I'm certainly not going to drive myself crazy trying to get that ES under 10 fps. Don't get me wrong, if I was shooting for money, then I'd care a bit more, but 99.5% of us will never see that difference on target, imo

Well said. I think too many focus on ES and SD, even though the gun shoots great. My wildcat as an example, shoots the 28g barracuda hunter extremes at around 1003 FPS. I switch over to the JSB 33.95 MK2 heavy’s and at around 945-950 FPS, at 50 yards the POI is a half inch below the BHE groups, and just slightly to the right. Not a big deal, really, for a spread of almost 60 FPS.



i know at a 100 yards it’ll show more of a difference, but how often do I ever shoot at a hundred?

 

[Corvid_hunter]

Thanks for all the replys gentlemen. I went out the other day and the results with the hammer spring maxed out and the valve at line #4 were:

110bar 934fps

120bar - 965fps

130bar - 981fps

135bar - 990fps

140bar - 1004fps

I turned the hammer spring down (15.86mm) and ended up at 968fps.

I turned the valve down to 7.76mm and ended up at 950fps on MAX with 35gr slugs.

I'm guessing I'm in the 3-5% below the plateau if what I have been reading I comprehended correctly.

I tried some groups at 30 yards and it might be working out with these slugs I made. I did take a shot at 118 yards and was about 2" off my aim point which I didn't think was too bad. There was a bit of wind and I have a rough zero at 30 yards. I hope to get out in the next day or two and try some groups at 50 yards and 100 yards if I have enough air left.

 

[Rallyshark]

Awesome, I look forward to seeing how it does with more testing!

 

[monstr2]

Did you open the Valve knob out to 6 lines to see if that increases the speed becoz my 25 Impact the factory shroud comes in the way & i cannot move the valve knob more than 4 and a half lines?

 

[bigHUN]

Did you open the Valve knob out to 6 lines to see if that increases the speed ...

Be careful with that, Do it only if you have the rubber ball behind the Valve Spring. My 2mm Valve oring jumped out of hole because I didn't had the rubber ball in the Valve knob at the first power tune, now I learned the lesson. Just saying...