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Tuning Power Plenum DIY my result

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Max115

Max115

Member
Jul 15, 2018
1,646
1,153
BC, Canada
This is my new video on installing my power plenum on my FX Impact MK2. I got the parts about 6 months ago and I finally edited and got the video up.

There are better instructional videos out there and this is just my version with pictures only for the DIY. I later did some velocity testings and found that with the original hammer spring, the gun will shoot higher velocity than the plenum kit spring. This was great but I wasn't able to obtain lower velocity by adjusting the power wheel. I ended up switching back to the kit spring and I was able to get better range of speed from the power wheel. But I lost the top speed at Max setting in the process.

I have been tuning my impact using the H&N 23gr .218 slugs. I have tried the NSA 23gr but no tight groupings out to 90 yards. The H&N slugs seem to work best in my gun with my setting with 125BAR, Max, and valve adjuster at line 4. My velocity was 945fps and I was able to consistently get 1/2 - 3/4" group at 90 yards. However with the new H&N slugs that I purchased recently, I haven't been able to get the groupings tight as before. These new H&N has a heavy white lubricant on them. My gun didn't not like them at all.

Now I am thinking of switching back the original spring and increase the velocity and maybe try the NSA slugs again or with these new H&N slugs.

What are the settings that you use for your Impact MK2, 600mm slug barrel. What slugs work best for you?

thanks.

here is the new video, enjoy.

https://www.youtube.com/watch?v=VM9_HV97zxQ
 
@Odoyle. thanks for the tip. I plan to crank it up and see what happens. My impact has been shooting well with the older tins of H&N 23gr .218 at 945 fps. I was getting 1/2"-3/4" out to 100 yards, but the new tins that I got where they were covered with greasy white lubricant. They don't work at all in my impact. Hence I am trying to make adjustments by washing and lubing the new slugs and shoot them at higher speed. Slugs tests video to follow.

ps. I was out shooting a bit today by increasing the Reg to 135 bar from my 125 bar set up. Velocity only went up to 946 fps with the 23 gr slugs. I think I will switch back to the original hammer spring to gain the power and see if these new slugs would get tighter group at 90 yards (test range).
 
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@Blejda. in time. I have to sort out the new H&N first as I bought 12 tins and they are all coated with the white lubricant. I have washed and lubed them and seems to get a bit better group but still not as tight as the old ones that I had. I was having really good groupings with the old tins, but now it is just frustrating not be able to get the accuracy as before.
 
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I think the best combo for power is using the original valve return spring that goes inside the plenum, original hammer spring, and original rubber ball valve adjuster. (No spring under valve adjuster)

Then upgrade the rest as normal, new valve house, plenum, hammer, hammer weight, valve rod.

I've heard its possible to do this "hybrid" upgrade and you'd have more adjustment possible IMO.
 
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I think the best combo for power is using the original valve return spring that goes inside the plenum, original hammer spring, and original rubber ball valve adjuster. (No spring under valve adjuster)

Then upgrade the rest as normal, new valve house, plenum, hammer, hammer weight, valve rod.

I've heard its possible to do this "hybrid" upgrade and you'd have more adjustment possible IMO.
Click to expand...

Glem is right, for big Hp a combo of old and new work great. One thing you'll need to know though. If you want to move the valve spring in side the plenum you'll need to add a 12mm spacer to the spring. If you dont the, the mkii spring is not long enough to hold tension on the valve. The dewl time will go off the charts. And your gun will very weird to tune. I personally have my .22 Impact set up this way. I have no problem sending 25gr at over 1000 fps at 125 bar on the regulator, with a SD less then 2fps. The valve stop makes it really easy to tune, you'll be able to get great standard deviations at high power.
 
Upvote 0
I think the best combo for power is using the original valve return spring that goes inside the plenum, original hammer spring, and original rubber ball valve adjuster. (No spring under valve adjuster)

Then upgrade the rest as normal, new valve house, plenum, hammer, hammer weight, valve rod.

I've heard its possible to do this "hybrid" upgrade and you'd have more adjustment possible IMO.
Click to expand...

Glem is right, for big Hp a combo of old and new work great. One thing you'll need to know though. If you want to move the valve spring in side the plenum you'll need to add a 12mm spacer to the spring. If you dont the, the mkii spring is not long enough to hold tension on the valve. The dewl time will go off the charts. And your gun will very weird to tune. I personally have my .22 Impact set up this way. I have no problem sending 25gr at over 1000 fps at 125 bar on the regulator, with a SD less then 2fps. The valve stop makes it really easy to tune, you'll be able to get great standard deviations at high power.
Click to expand...

Where theory meets reality haha, thanks for that good to know. 👍

Do it Max!
 
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@Glem. thanks for the tips. I am not very clear with the parts mentioned, but I know the original hammer spring will give me the increase velocity. I will try that mod first as my intention is to push these 23gr slugs faster to see if I can get tighter group. At this point, my previous tune with 125bar, Max hammer, and line 4 gave me the best tightest group possible at 100 yards before. But that was with the older H&N slugs. The new slugs are the one that gave me these bad accuracy issues right now.

@Mrshosted. sounds a bit too complicated to me at this point. I will keep that in mind and might try your method once I have a clearer head or after I get some tighter groups with these new slugs. My Impact is still shooting the AA 18gr pellets well out to 100 yards for my pestings, so I don't really want to mess up my gun too much, lol.

thanks guys for the info.
 
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MK2 PP here, .25 and 700mm.

I did replaced the C7 hammer spring to old longer longer one (pre PP) and replaced the valve spring C42 to a softer from the new the slug kit (I did not buy the slug kit but found a similar spec spring in automotive service store 0.58x6.5x45) and put the rubber ball A16 in for safety only at the back of a spring.

110 bar, hammer spring wheel @4 and I believe more then 10mm on a slider (because of a longer spring), and the valve adjuster way out of 4th line.

960 fps with 33.9gr JSB's lowered to 920 for ES stock Humma dual port (not modded yet waiting for other spare parts).

So I have about 10 mm hammer spring tension in reserve, right now is only touching the spring holder C8 before cocking, and I don't think that the valve rod C1 is touching the rubber ball. Not fully tuned only a ballpark.

Also I just spent two half days washing/drying/sorting/lubing five tins of pellets, tomorrow is a day to clean/polish the liner.
 
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