Hi everybody. New member I need your help please. I am trying to create a new plenum for fx impact mkii .cal.It supposed that my gun(I am going to receive it few days)will have a valve tube 25 percent larger . My question is is necessary the extra plenum to achieve the hi speeds I see in this forum? I want to make all these modifications to shoot slugs . I can understand from some photos the upside thread M14x1.5 which is connected in the rear block. What I don’t understand is the down side of the tube where the gauge is located . I mean the bottom of the plenum is a big piece with thread ? I can not understand how can I create in lathe en empty solid tube. Can somebody provide me any schematic with dimensions please? Sorry for my bad English is not my official language. Thank you in advance
Fx impact external plenum
- Thread starter Chris1973
- Start date
More plenum volume allows for more efficient air during the shot. Because you are getting the 25% larger plenum tube and accompanying benefits you should not need additional air from the added plenum canister.
Here is a canister plenum someone else did this to get more air volume:
https://www.airgunnation.com/topic/larger-plenum-test-on-impact-x-30-700mm/
Here is a canister plenum someone else did this to get more air volume:
https://www.airgunnation.com/topic/larger-plenum-test-on-impact-x-30-700mm/
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An external plenum is not necessary in .22, the high fps is the result of porting the brass transfer port and pellet probe. Most of the guns you see with an external plenum have been modified by Ernest Rowe and include a dual transfer port. I believe my gen2 impact with a 5.8mm valve seat and elongated transfer port achieves the same or higher velocity than the modified MKII... but only in .22 caliber. Larger caliber barrels on those guns will be much faster than mine due to larger valve and plenum.
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I have my .25 caliber, 700mm MkII set at 150BAR and I got 980fps with the 33.95gr this morning. I almost maxed out the hammer spring and dialed the valve adjuster all the way out. That's pretty hot for no internal adjustments. It didn't shoot well of course, I turned it back down so I was getting between 930-935 for best accuracy. The power is there for when the slug liner arrives tough.
Stoti
Stoti
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My new mkii is a 30 cal. I hope the original valve tube of mkii is big enough and after all the all the modifications , hammer weight, enlogated TP etc I will manage to have respectable speed for slugs.I want to say a big “thank you” to all members of this forum. I am watching all the topics regarding impact last months and i learn so many things for all internal parts of this fun before even I bur it. Your job is really appreciated . I bought as well a LW uncooked blank barrel 1.16 twist. I really don’t have any idea if is polygonal or no. I am planning to modify it and install it in impact because the 0.30 cal liners from fx maybe will reach in my country after a year. Do you have any idea if this barrel is a good choice? The only access I have in slugs in local market is NSA slugs.I have a Daystate Wolverine hilite 303 and I am very happy with these slugs. Specially the 55 gr at 940 FPS. Is the stock LW barrel choked with 1:18 twist.
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Full of mistakes before forgive me is my first post in this post and I am writing fast from my mobile. Uncooked barrel!! Lol!ll no choked i mean....
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The external plenum alone will not do anything for you. You need a hammer weight, and need to open up the valve housing for more air storage and air movement.
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The external plenum becomes part of the same regulated air storage as the valve housing. Mr Rowe only removes a portion of the valve housing to give an unobstructed path to the external plenum. More plenum is always better to reduce pressure drop but won't be as apparent on the small calibers because they see much less pressure drop. The hammer weight only helps open the valve beyond 145 bar or so. At lower regulated pressures it causes too much dwell time on the valve and beats up the valve stop. The trick is finding the right combination for the power you want to make. The most needed improvement for the Impact is a larger valve. 8-9mm would be awesome but bigger equals harder to open and more vibration opening it.
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The external plenum alone will not do anything for you. You need a hammer weight, and need to open up the valve housing for more air storage and air movement.
That scope looks tiny!
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Thank you for your help. May it seems full to try to make all this modifications in a new gun but I have the feeling that in bigger calibers like 0.30 is necessary. I am just trying to achieve speed around 950 FPS with a 50 gr slug. As I wrote already I didn’t even receive my gun yet. Next week hopefully but last 2 months slowly I prepared too many parts.I made 2 different hammer weights 6 and 6.5 grams. I made as well a few valve seats 6 -6.3 and 7 mm . I am trying this week to make a full rod from titanium but is a little headache.All the CNC services I visit they say to me that is a very small dimension for their machines. I am still searching. I bought a valve housing and I made a little bit larger the TP ( in the length) and I milled the down side for best air path in case I will install an external plenum( I hope will not be necessary).I am trying to make and some different sizes derlins for the valve stem to much in bigger valve seats. I am trying to explain you that I made all the known modifications before I ask you for the external plenum. And all of these of course with your help. As I mentioned before your love and your job for this gun help us to understand all the internal parts of this gun even before we bye it. A huge thanks from my heart to Mr Ernest( he is all day in our Tv last months my wife is ready to kill me ) and a huge thanks as well to all the rest members of this forum. All your recommendations for many mods of impact last months have been saved as shot screens in my favorites.
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I am a hunter since 8 years old and I am now 46. I started with floberts 9 mm and after shotguns ( driving hunting wild boars all my life) and of course shooting all day with dianna Airguns as a child. In my country is not allowed hunting with any type of rifle or Airguns. Last 5 years I am resident for work in a country in the Middle East. That means no hunting and no shooting for long long time. Two times per year I am visiting my favorite mountains in my country to enjoy my favorite sport . Imagine all this madness with fx impact just to shoot targets one month per year. A Schmidt & Bender pm ii 5-24x56 for my impact has arrived in my house ( in my country) last February and still I didn’t touch it!!! I bought yesterday 34 mm Warne quick detach rings and I am thinking to install a utg super slim 20 moa rail . I know !!!!! If we start adding the dollars I will start crying! I could by a used car. But ok ! I learn to think like this : bye once cry once as you say in USA ( that’s for the scope ! For the impact I don’t think so with what I am reading so far).Anyway I think that I started this sport with pcp’s with good and quality equipment before 3 years . Daystate 303 wolverine hilite with a Delta titanium 3-24x56 . The gun no issues after 10 k shots. Just once in 3 years I change myself all orings. I store the gun for a full year in 150 bars and I am finding after a year in my vacations with 150 bar.No creeps! The scope as well amazing crystall and amazing tracking. Counting the days already to go vacations beginning of June! For the moment I have the time to prepaire all the mods for the new gun......
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The external plenum alone will not do anything for you. You need a hammer weight, and need to open up the valve housing for more air storage and air movement.
Correct, my point was that just adding the plenum will do nothing. The hole that goes to the reg gauge is tiny in the valve housing. Earnest helped my do my gun when he visited us here at the shop. Yeah the scope is tiny, my Hawke sidewinder started walking and I put the Athlon on while I sent the Hawke back for warranty.
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That's easy since I have reached 970 fps shooting the 50gn JSB in the 700mm Impact X.
You need at least a 5.8mm valve seat. Larger is better.
A regulator capable of 170 bar
A6.5 gram hammer weight.
Replace the C3 bumper with delrin.
Make the brass transfer port egg shaped, elongated toward the pellet but not wider. Break any sharp edges.
Drill the entry hole of the pellet probe larger than the port feeding it and knife edge the edges.
Remove the top half of the pellet probe from the entry hole forward and knife edge all the cut edges.
You could $hip your gun to FX USA and have Ernest Rowe tune it to the power level you choose. His method is far more efficient reaching 950 fps or more under 150 bar with a much higher shot count than I get... even with a 600mm barrel.
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Thank you Heavy -impact. I mis to write that I order already a Huma regulator extra high speed. I receive it before few days. The derlins that are going to replace the c3 are ready . I am waiting only the brass piece and the probe so I can try to modify them with a dremel carefully.Unfortunately I can not ship my gun to Mr Ernest from Europe. I wish I could but is not easy. Custom issues. After reading all the posts in the forum for impact mods I understood(correct me please if I am wrong) that Mr Ernest double port in brass piece and probe is working better in combination with his external plenum. I mean in Mkii if I will not add an external plenum i( because it has from manufacture already big enough) is better to make it as you describe to me above?And no dual ports? And if I will not add an external plenum may is wrong that I mill already the valve housing ? You know what I mean . No the tp of the valve housing. I mean all this piece I mill in the length of valve housing for better air transfer from the ex plenum.
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I'm not sure where you're milling, the valve housing or the rear block where the regulator gauge goes.
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I am talking for this one. Obviously this has be done for best air path from external plenum. If I don’t install an external plenum is still ok? Because I already milled it like this and probably I will not install an extra plenum .
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The photo is from the forum. Is not mine but I made it same. And I am also a little bit confused with OM valve housing for last impact mkii. The VH I bought is a full body only with the small hole for the bar gauge contact.I see in another dealer site a valve house with 3 long openings . When I order it I gave the code from the latest schematic of fx. I am curious with which one is coming the new impact.
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