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Tuning need some impact k2 700mm help...

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dannya1a

dannya1a

Member
Nov 29, 2019
408
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Nys, United States
so trying to find and efficient tune to shot my boat tail 39 gr hollow points. this is a power plenum model and i have both superior liners. currently it is loud and terrible shot count. I have watched Earnest Rowe's videos on tuning so i'm familiar there. impact also came with the slug power kit installed as well.

I currently have reg at 125 bar. power wheel on max. hammer spring is 18.60 mm. valve adjuster at 10 mm. i'm seeing 910 fps over the chrony. I watch during a 5 shot string and i used 20 bar of air. that seem way excessive. it also loud. so i know it isn't right.

i'm hoping to get to 920 fps, but way more efficiency. currently according to my math. I'll only get about 30 shots. thats terrible. 
 
I have no experiance with thouse particular slugs, but basically you have to know what your max speed is, where you do not gain more speed on a given reg setting, when tuning. You have to make sure you are 10-20 fps or more, below that speed, to make the gun efficient. When you say the gun is very load, you may are shooting at the max speed, and are wasting air?
 
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Once you get the power wheel fixed so you can actually use it, you'll be able to dial it in. You can play with the valve knob in the meantime to try and get better results, but the hammer spring tension is a key part of dialing in an Impact. You can also work with the HS block tension too, which is even a better avenue to take until the PW issue is resolved and you can spin it around and it stays put where you put it.
 
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Once you get the power wheel fixed so you can actually use it, you'll be able to dial it in. You can play with the valve knob in the meantime to try and get better results, but the hammer spring tension is a key part of dialing in an Impact. You can also work with the HS block tension too, which is even a better avenue to take until the PW issue is resolved and you can spin it around and it stays put where you put it.
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i got it staying put is "3" now. but "c" is still not holding. just seems crazy to only get 30 shots on a full tank
 
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Open your valve to fully open or just pass 4 lines and increase your regulator to 150bar and see your max speed. Once found max speed then reduce the valve till speed drops about 40FPS and that’s your fastest and somewhat efficient tune. Listen to the sound On each lower setting until you hear the PPSSSSSssss go away then that’s your sweet spot or most efficient and fastest tune. Then harmonic tune at lower speeds/settings.



You may need superior heavy liner since boat rails are usually a bit longer and need faster twist rate. What’s the length and BC? 


Also at that power level 2 mags or 50-60 shots is already very optimistic. Why do you need to shoot so fast? My best groups have been at lower speed(mid 800 FPS) actually. 
 
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i have the heavy liner...my boat tails are hollow point and weigh 39 gr. they are .335" long and have a listed BC of.0599 estimated
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In ballistic stability calculator with the heavy liner you can shoot accurately even lower than 700FPS so no worry on the twist rate even if you don’t get the full twist rate because of the smooth lands. So just try to shoot some groups at 900, 880, 860 all the way down to min to see which one groups the best. Also with heavy liner I would recommend earnest row’s carbon sleeve and barrel tensioner because harmonics will be harder to control with that much power. 

IF you want 900+ FPS your regulator will need to go to at least 140 to get to that level of power. 800FPS isnt hard to get to but 900 and 1000fps takes considerably more power to over come the friction to achieve that amount of acceleration. 


i don’t know what you are trying to hit but even at 800 FPS that’s a lot of power! 
 
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What’s your max speed? Back the thumb adjuster off to line four. Leave power wheel on max then shoot over the chrony again?



report back with that speed? 


If your desired speed is 920 you need to get the gun to shoot 935 ish with everything on max. Then you begin to back off the power wheel. Once you get her down to 920 ish she will be in an efficient tune. But your not done there. Begin to fine tune these settings.


Make micro adjustments to the power wheel via the adjuster screw. I personally don’t use the thumb adjuster I back that all the way off so it’s not being used. Focus only on the power wheel and the adjuster screw. 
 
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ok so at max speed i see is 900 fps average across 8 shots with es 7 and 2 sd. reg set at roughly 127 bar. hammer spring is at 19.60 mm. Its currently using 20 bar for 10 shots. thumb adjuster out at 11.37mm

so i'm guessing i need a bit more regulator pressure to get up to the where i'd like to try. 

to add more i just made the decision to try for dual tune and be able to use my 29.2 gr hunter pellets with the gun set on minimum. if i have to lose some on the top end to get it then i will.
 
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ok.. i think i'm getting a handle on the impact. pic is a group at 43 yards with my 39 gr hp boat tials, using the superior heavy liner. 845 fps 60 fpe. sound is getting quieter, and air usage is getting more efficient.

20201123_145806.1606163445.jpg


so it appears these slugs don't care for excessive speed. still got more work to do to get it to tighten up the group. cold and windy here today. hopefully tomorrow will be less wind so i can get out to farther range with testing.

power wheel at 3. 8.35mm on valve adjuster and 21.85 oh hammer spring in position 3. still 127 bar on reg. shot count is increasing.
 
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Nice! When a slug with sufficient spin or accurate when it’s at lower speed becomes inaccurate at higher speed it’s likely caused by harmonics. This can be helped by adding carbon liner sleeve and barrel tension spacer or carbine tension sleeve Ernest Row makes. Once you find a happy setting try adding the carbon sleeve and I think you can push the speed up a little with harmonics controlled a little better. 
 
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I think that may be the next thing to test. I’m also thinking of playing with the slug seating depth as well today. I know current setup is seating the slug well past the transfer port hole. I also found it odd that my liner had 4 orings on it when I pulled it out, figured it would only have 3. But this may be due to it being a 700 mm barrel. 

Certainly more testing to be done.
 
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did some screw work on the power wheel. my screw is now 9.40ish mm long, and it appears that i may finally have setting "C" staying put. but if it lightly touch the wheel it will jump to the lower setting. so still not at 100%. the replacement parts should be here today though. I have since detuned a bit, and switched to a tune that is working well for my 29.2 gr pellets. and took 2 grey squirrels toady. one at 35 yard and the other at 43 yards. 

I'm not giving up on slugs. I just called NOE and checking into my die body order. During out conversation, and slugging the superior heavy liner. Al told me the we can drop to the .243 cal cal sizers and get slugs sized down closer to the choke size of the Superior liners. I pushed a .249" slug through the heavv liner and it came out as a .244-.2445" .Using the sizing kits you will need to get a smaller pushrod to go below the .25 cal air gun sizer bushing. the rod for .25 air gun is .245" dia. so just figured i'd pass some info on in this area.

So maybe with my cast slugs sized down closer to the Superior heavy liner choke size, my groups may improve and get tighter. Time will. tell. It gonna be a bit till the sizing stuff gets here. Once i get things tested I'll report back on my findings.
 
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got the new power wheel parts from FX.. new power wheel did the same thing, but i did have to use the screw they sent as mine is now too short and when installed the wheel wouldn't turn. so then I changed out the grub screw. that seems to have done the trick. with my old wheel back on and the new design grub screw, its currently holding the setting where i put it,. But i have not tried to dial in more hammer spring as of yet, because my tune is working well for my pellets currently. So those who come across this problem it appears you'll need the new design grub screw.
 
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