Tuning How to tune MK2 with power block upgrade kit?

[bigHUN]

I have seen some conversation earlier months but I never really pay attention, until I made my own upgrade last weeks ... and now those advises are buried pretty deep in the threads when I try to search. And I would welcome an advise.
Impact MK2 PP upgraded to a Power block + 720c plenum kit.
- Heavy HS + tungsten 14 gram HW + heavy VS;
- .25x700 liners (tried both Superior Heavy and currently installed STX-A Pellet) + high flow transfer port + high flow pellet probe;
- JSB 34 gr MK2's, with in mind that later along the season I may jump into 37-41 gr slugs for longer ranges;
From last year 130 bar tune after upgrades the speed got high 980 ish, so I lowered the Reg to 115 bars and tightened the VS that lowered the speed to 915.
The Power Wheel at Min with some slack play - the PW doesn't increase but lowers the speed.
Raised the Reg to 140 bars, tighten the VS only to put the speed back in a ballpark of 920 ish, and the PW still doesn't raise but lowers the speed.
VS adjuster started from 5th line and currently got it about 3.5 th line.
Shot a tin of .25x34gr pellets today at my club, 50 meters, the rings POI looks acceptable about MOA with some occasional flyers or the groups wandering around as I play with tune.
Tried the ballpark of 915 to 927, SD less then 5.
What I am missing with a Power Wheel? some logic telling me I shall raise the Reg from 140 b much higher? Or replace the VS to a softer?
Open to suggestions.

 

[bigHUN]

Forgot to say, the 34gr JSB MK2's washed and lubed only, but unsorted... that may explain the flyers up to some level.
Today excercize had a purpose only to make the Power Wheel work, but unsuccessful.

 

[Airgunmann]

You probably need to raise the reg pressure yet

 

[DanT55]

Im running a Huma two stage reg on my MkI with a power block/plenum upgrade, standard hammer and spring that came with it, high flow STX 600mm barrel and pin probe, standard valve spring. 1st reg at 145 and 2nd at 100b. I also upgraded to a Mk3 power wheel for more HS tension at max without a lot of adjustment due to the bigger cam wheel. Getting easy 880 with 34gr JSB's and ZAN 34gr slugs. SD in the 4's.

I don't think you need that heavy tungsten hammer at those pressures which can be counter productive. I would dial reg down and put in standard hammer, Max HS and valve adjuster out to 4 line or just past. Work from there.

 

[tdhouser1964]

Almost sounds like you have too much hammer spring and that extra heavy Tungsten hammer weight isn't helping either. You're still shooting 33g with a 50g tune..

 

[bigHUN]

This what I was scared to play with, an overweight on hammer, but needed somebody to hold my hands before I do a deep surgery again
Looks like a new project this evening.

 

[Trucker3573]

I would put the PW to max and mess with the internal hammer spring to find the max velocity the gun is capable of at the given reg pressure. If you use that approach the power wheel will work as you want and give you the max range of adjustment for a given reg pressure. It will also tell you immediately where you need to go with the reg pressure to achieve the velocity window you are looking for.

 

[bigHUN]

I like the logic of troubleshooting the PW with Max but that will probably put the Reg way above 150 bars which I think for pellets would be overkill.
I would like to find the sweet spot that I can shot this .25 MK2 both 34 gn pellets and 40 gn slugs

 

[bigHUN]

The surgery is done. I removed the 14 gram tungsten weight and replaced with 8 gram brass, also replaced the VS with 2mm shorter.
Now I have to wait again two days for my range tuning.

 

[DanT55]

Start with a low reg pressure with hammer wheel at max and adjust tension screw as needed. With that big plenum you should not need much reg pressure to hit target V with 34gr pellets. Less is more.

 

[EliteAirCustoms]

I fully agree with the hammer weight. I had the exact same issue as you. Increase on the wheel lowered the power. I went back to the factory hammer weight and all is good.

 

[bigHUN]

I did some garage tuning in the morning, you must be right:
8 gram brass hammer weight vs OEM 6.7 gram stainless:
Started with 100 bar on Reg and got to 125 bars, all time the power wheel behaves opposite - increasing Hspring tension lowers the speed - and decreasing Hspringtension increase the speed. Very oposite what I got used to PP (MK2 power plenum).
Later tonight I will put back the original hammer weight to prove it to myself ???
Interesting ... what a bigger 720c plenum can do vs 520c or lower.

 

[Airgunmann]

I'm using a tungsten hammer a 720 plenum and running reg at 155 with 30 cal mk2 molded 51 gr pellets I'm getting 920 with out power block going to try some 56 gr pellets hope to get them to 900 with out bumping up the reg to much but my power wheel is working correctly

 

[bigHUN]

Hm ... this big 720c plenum + powerblock is getting tricky.
With a 520c power plenum I was shooting slugs to 100 Meters - upgraded to a 720c power plenum to shoot further longer distances.
My ultimate goal was to - dial the power level - with a short dwell high burst
.25x700 with pellet and .25x600 for slug,
because these two projectiles/liners eventually need a different powercurve

 

[Ctkny]

Dump the hammer or up your reg. Heavy hammer you loose fine tune with power wheel. Heavy hammer is only needed over 155 every time I tried with my setups.

 

[Trucker3573]

I like the logic of troubleshooting the PW with Max but that will probably put the Reg way above 150 bars which I think for pellets would be overkill.
I would like to find the sweet spot that I can shot this .25 MK2 both 34 gn pellets and 40 gn slugs

The PW can be tuned at max setting with any regulator pressure by using the internal HS adjuster. That is how you get the most range out of the PW at whatever reg pressure you desire.

 

[bigHUN]

Yes I agree, that is how I had it with original PP on MK2. But this bigger plenum tuning messed my mind up. I cannot doit in my garage much loud, I need to go to an open space range.

 

[Seeker]

Heavier hammer adds more spring preload. Your spring may be overcompressed and the hammer hits the valve seat with less energy.

Also - one change at a time. If you installed PB then leave the hammer and hammer spring the same as well as the reg pressure.

 

[bigHUN]

- one change at a time. ...

To late advise ;(
I have removed the heavy tungsten weight and put back my old brass weight (8gr vs FX original 6.5gr if I can recall it correctly).
That was last week, that yes the hammer weight was "overweight" but the spring had a slack, and when I increased the Reg to 150-160 and because of a slack in spring the HW just bounced back. Or something like that.
I had some raining and storms in past couple days not really suitable for the range ...
I like to do initial tuning at least 50 meters and shooting paper rings at least a 100 pellets or slugs, and I call that a "ballpark" only.
I move over to 100 meters and fine tune there. Easier to read the errors.

 

[EliteAirCustoms]

I went back to the factory hammer weight. Power wheel working just as it did before the PB. However, with the PB I'm able to run at a much lower reg setting to achieve the same FPS as the old block. At 100 bar I'm getting tons of shots and tuned to 915 fps on JSB Hades in 25 cal, 700mm superior heavy to speed up my twist rate, PW on 3 with room to move in either direction. Half inch groups at 75yd and only 2-3 fps deviation. Loving it now that I've found the sweet spot. Can't wait till bushytail season.