Can you tune a external Plenum like the power plenum?

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sigp220

sigp220

Member
May 12, 2018
250
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NE, United States
Several months back I purchased an Impact MKII with a power upgrade. (external plenum, heavier weight hammer and the transfer port opened up).

Having watched Giles video several times. I was wondering if I could turn my regulator down to 110 bar and increase my shot count?

Right now I'm setting at 150bar, hammer maxed, shooting 1040fps with a 30cal. getting a magazine and a half on a 580cc bottle.

Am I all wet wanting this? Did I miss something along the way? If possible what do I need to do?

Oh I'm also looking for that sweet spot for shooting 44gr pellets which I believe is 920-880 if I'm correct.

Thanks in advance


 
Yep , like Dillon said you should be able to reduce the reg pressure with the other plenum you installed. My question is why are you shooting pellets at that speed? I think you’ll find that pellets are usually most accurate when shot between 820 and 920 fps with a few exceptions where they can be shot a bit faster. There’s a really good video on airgun101 that speaks about the transonic zone and why you shouldn’t shoot there. 
 
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Hobbyman2007

Those are the speeds I'm looking for roughly 820-920fps. Having listen to what others have said I went with the velocity tune. Find your max reg pressure and max velocity. Now I'm looking to see if I can't step that down and find the max shot count and velocity sweet spot.

Centercut has stated on several occasions if your shooting over 940fps your wasting time and air.

I'm trying to figure out how to step it down now.

PaniSd: Could I bother you for your Hammer spring measurement and micrometer setting. My hammer spring is set to 15.7mm and micrometer to 4 lines showing. Your settings look like a good starting point.

Dairyboy: Thanks there is hope for me.
 
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Several months back I purchased an Impact MKII with a power upgrade. (external plenum, heavier weight hammer and the transfer port opened up).

Having watched Giles video several times. I was wondering if I could turn my regulator down to 110 bar and increase my shot count?

Right now I'm setting at 150bar, hammer maxed, shooting 1040fps with a 30cal. getting a magazine and a half on a 580cc bottle.

Am I all wet wanting this? Did I miss something along the way? If possible what do I need to do?

Oh I'm also looking for that sweet spot for shooting 44gr pellets which I believe is 920-880 if I'm correct.

Thanks in advance

Click to expand...

Most likely its one of my external plenum with 1/8 28 or m14, if you want to shoot 44gn jsb with 700mm the reg pressure would be around 105-115b with the speed of 875-900fps+ depending on HSTA preload and Valve adjuster adjustment. With mk2 reg tube and external plenum has 68cc combined volume.



Ernest
 
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Most likely its one of my external plenum with 1/8 28 or m14, if you want to shoot 44gn jsb with 700mm the reg pressure would be around 105-115b with the speed of 875-900fps+ depending on HSTA preload and Valve adjuster adjustment. With mk2 reg tube and external plenum has 68cc combined volume.



Ernest
Click to expand...

Do you know what the volume of the power plenum is? Just curious if it is more or less than the the external and MKII together.
 
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I have mine tuned hot w/ similar mods as you. Flinging a 44.75gr .30 at 1000fps.

Tuned by FX.



The pellet doesn't like that speed and accuracy falls apart after 50yds This gun has done better. A lot better.

Even with the power wheel set at min it's still over 920fps and is not accurate to my satisfaction.



So my options are:

a. Turn the power down

b. Fling slugs.



Being who I am option a wasn't really an option. 

So I've ordered a 700mm and slug liner from Utah. We'll see how it does when they get here.

My Impact:

1578240174_3878472625e1208ae34c0a0.53274322_ImpactWithClague.jpg

 
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Most likely its one of my external plenum with 1/8 28 or m14, if you want to shoot 44gn jsb with 700mm the reg pressure would be around 105-115b with the speed of 875-900fps+ depending on HSTA preload and Valve adjuster adjustment. With mk2 reg tube and external plenum has 68cc combined volume.



Ernest
Click to expand...

Do you know what the volume of the power plenum is? Just curious if it is more or less than the the external and MKII together.
Click to expand...

I believe its 65cc, someone can confirm though.
 
Upvote 0
Most likely its one of my external plenum with 1/8 28 or m14, if you want to shoot 44gn jsb with 700mm the reg pressure would be around 105-115b with the speed of 875-900fps+ depending on HSTA preload and Valve adjuster adjustment. With mk2 reg tube and external plenum has 68cc combined volume.



Ernest
Click to expand...

Do you know what the volume of the power plenum is? Just curious if it is more or less than the the external and MKII together.
Click to expand...

I believe its 65cc, someone can confirm though.
Click to expand...



https://www.krale.shop/en/power-plenum-kit-fx-impact.html



They say:



"With this Power Plenum Kit for the FX Impact the plenum capacity will be increased to 54 cc"
 
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I'm almost spot on 921fps at 110bar, max on the power wheel, 4 lines on the valve adjuster.

Only question, Min setting on power wheel gives me 907fps average. The spread in velocity seems rather small.

Should I back off the HSTA or just make adjustments in the valve adjuster? My thoughts on this again and I might be way off base. Is that I would have a larger spread on the power wheel. Like 40 fps. I know on a standard factory set up this seems to be the norm. Am I missing something?

Thanks to all that have replied and MonsterMax for the cool pick. Yep that's what mine looks like but I have a super size Donny. Let us know how the slug liner works for you.




 
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I'm almost spot on 921fps at 110bar, max on the power wheel, 4 lines on the valve adjuster.

Only question, Min setting on power wheel gives me 907fps average. The spread in velocity seems rather small.

Should I back off the HSTA or just make adjustments in the valve adjuster? My thoughts on this again and I might be way off base. Is that I would have a larger spread on the power wheel. Like 40 fps. I know on a standard factory set up this seems to be the norm. Am I missing something?

Thanks to all that have replied and MonsterMax for the cool pick. Yep that's what mine looks like but I have a super size Donny. Let us know how the slug liner works for you.



Click to expand...

Maybe go a bit more on reg pressure to get all on a bit more 950fps for example. Use the valve to find a good speed for accuracy going down from 4 lines. What is called sweet spot is the point where you reach good accuracy with low spread in fps. 

Im now on 15mm hamer 960fps 125bar and gong down with valve ... find the best accuracy at 915fps with spread of just 3fps and many duplicates ... some time up to 5 in a row and its fx amp reg... that I belive beats huma reg in many things like filling speed, less reg pressure diference from 250 down to 150bar etc.

So, its just examle of my practice and that way worked best for me. 
 
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You can shoot the 44.75 pellets out of a 700mm slug liner at 1000 ft/s and they will all go into one tiny little hole at 50 yards. A long time ago I discovered that certain pellets are accurate at much higher velocity out of a slug liner than they are out of the pellet liner. However, if you just want to shoot them at 880-900 ft/s they will be super accurate out of the pellet liner for you, and at that relatively low velocity you should get lots of shots. As with every thing else though it is a trade off between power and shot count.

As for the combined volume of your plenum set up, I have been told that the plenum on the MKII is 25cc. And I know for a fact that the volume of the Ernest Rowe plenum is slightly less that 35cc because I measured mine. So if it is true that the MKII plenum is 25cc then the total volume would actually be 60cc not 68cc. FX has not confirmed the volume of their plenum for me yet and I have not tested mine. Does anyone here know for sure what the MKII plenum volume is? And by the way, I measured the volume of my external plenum using a syringe and whether it is marked in cc or ml does not matter, those are just two names for the same thing.
 
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I have mine tuned hot w/ similar mods as you. Flinging a 44.75gr .30 at 1000fps.

Tuned by FX.



The pellet doesn't like that speed and accuracy falls apart after 50yds This gun has done better. A lot better.

Even with the power wheel set at min it's still over 920fps and is not accurate to my satisfaction.



So my options are:

a. Turn the power down

b. Fling slugs.



Being who I am option a wasn't really an option. 

So I've ordered a 700mm and slug liner from Utah. We'll see how it does when they get here.

My Impact:

1578240174_3878472625e1208ae34c0a0.53274322_ImpactWithClague.jpg
Click to expand...

Switch to 52mm hammer spring so you can get 150fps speed variations between max and min fined tune with preload screw. Or adjust enough reg pressure to get certain speed fined tuned by PW and VA.
 
Upvote 0
Several months back I purchased an Impact MKII with a power upgrade. (external plenum, heavier weight hammer and the transfer port opened up).

Having watched Giles video several times. I was wondering if I could turn my regulator down to 110 bar and increase my shot count?

Right now I'm setting at 150bar, hammer maxed, shooting 1040fps with a 30cal. getting a magazine and a half on a 580cc bottle.

Am I all wet wanting this? Did I miss something along the way? If possible what do I need to do?

Oh I'm also looking for that sweet spot for shooting 44gr pellets which I believe is 920-880 if I'm correct.

Thanks in advance

Click to expand...

I tuned your impact for highest possible speed with your 600mm barrels. If you want max spread between max and min you have to change the 57mm hammer spring to 50 or 52mm springs that can be had at FX USA. Keep in mine With shorter hammer spring top end will be less but bottom end will be lower. With all my testing 700mm is more accurate then the 600mm .30 , In major 100y competition all .30 impact used 700mm. The external plenum has a shorter load time meaning the opening off the plenum is closer to the valve opening— will allow more volume of air in the barrel before the valve close.


Ernest
 
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Most likely its one of my external plenum with 1/8 28 or m14, if you want to shoot 44gn jsb with 700mm the reg pressure would be around 105-115b with the speed of 875-900fps+ depending on HSTA preload and Valve adjuster adjustment. With mk2 reg tube and external plenum has 68cc combined volume.



Ernest
Click to expand...

Do you know what the volume of the power plenum is? Just curious if it is more or less than the the external and MKII together.
Click to expand...

The FX power plenum is 54 cc.
 
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A correction needs to made at this point in our discussion.

My rifle was purchased from highly recommended tuner and smith (just as ordered). Just not Fx or Ernest. I felt instead of bothering my dealer with a couple of hundred of silly questions I'd ask here. 

An apology has been sent to Ernest for any confusion in the discussion.

With the knowledge gain here I've found out several things.

How to tune my rifle correctly and that my number nine double wide boot will still fit in my mouth easily.




 
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