Fx Impact Fix & Mods for more FPS / FPE

[mtnGhost]

Question, with the capability of running the plenum pressure at 125-130bar is there really a need for a hammer weight? I thought extra weight was really needed for like 170bar and up. Stu's kit does come with everything though.

jk

I stress tested my Impact yesterday with a 40cc ER plenum, mainly to put my mind at ease - but also to see what pressures 7 gram hammer weight could fully open my valve with (prior to my VS-integrated valve housing mod next week).

I turned the reg up to 200bar. The thin Delrin seal that I had been running under the reg gauge popped last week, so I made one thicker out of the strongest Delrin that I could find, around 3.5x thicker. I let it sit at 200bar for 45 minutes or so as I setup targets, I took a few shots, velocity was slow (~500fps), then I removed the CF bottle and just ran off of plenum pressure. It took a few more shots before the velocity jumped to where I expected it to be, right around 175 bar is where it came back to life (1037fps / 43.5gr). 

Shot count is pretty bad with 7 grams. I suspect that my next exercise will involve turning some new parts and cutting a bunch of springs that I have to find the optimal configuration. I'm strongly considering keeping mine as a 25 slug gun full time. I can't wait to run this 30" barrel with the 1:10 twist. 

 

[heavy-impact]

I can't wait to run this 30" barrel with the 1:10 twist.

That's a really tight twist, you planning on super heavy slugs ?

 

[mtnGhost]

I can't wait to run this 30" barrel with the 1:10 twist.

That's a really tight twist, you planning on super heavy slugs ?

52 grain mainly

 

[PaniSd]

Yep, external plenum helps a lot ... here is one guy made video with my 60cc external plenum.

He runs throe .25 couple of slugs up to 47grain at 145bar.

https://youtu.be/X8iR40qvJYM

 

[mtnGhost]

Yep, external plenum helps a lot ... here is one guy made video with my 60cc external plenum.

He runs throe .25 couple of slugs up to 47grain at 145bar.



https://youtu.be/X8iR40qvJYM

I would put a Wika on that.. those old FX gauges are +/-30bar. 

 

[Vadimas]

Was set for this slug bc 0.122.

I think that's a good indicator.

Slug 22cal 34gr.

 

[mrdirect]

I have read so much, that now I am lost.

I have a .30 with 44.75 gr JSB that does 940fps, so my gun is capable of that.

Now I change to a .25 caliber 39 gr slug (so lighter weight), but I cannot go faster than 900 fps.

I have already enlarged the pellet probe and slightly enlarged the brass port on the barrel.

Where is the bottleneck with .25 caliber? What area needs improving with .25 ?

As I said, the gun can do 44 grain @ 940 (in .30) , so why is a lighter .25 slower?

 

[Vadimas]

I have read so much, that now I am lost.

I have a .30 with 44.75 gr JSB that does 940fps, so my gun is capable of that.

Now I change to a .25 caliber 39 gr slug (so lighter weight), but I cannot go faster than 900 fps.

I have already enlarged the pellet probe and slightly enlarged the brass port on the barrel.

Where is the bottleneck with .25 caliber? What area needs improving with .25 ?

As I said, the gun can do 44 grain @ 940 (in .30) , so why is a lighter .25 slower?

Small caliber is harder to get through.

22cal will be even slower.

 

[edosan]

I have read so much, that now I am lost.

I have a .30 with 44.75 gr JSB that does 940fps, so my gun is capable of that.

Now I change to a .25 caliber 39 gr slug (so lighter weight), but I cannot go faster than 900 fps.

I have already enlarged the pellet probe and slightly enlarged the brass port on the barrel.

Where is the bottleneck with .25 caliber? What area needs improving with .25 ?

As I said, the gun can do 44 grain @ 940 (in .30) , so why is a lighter .25 slower?

Bigger cal have bigger transferports ergo more air lead to more speed (usually not always)

Your 0.25 porting probably is not ok. Please understand in the pellet probe you need to remove the O in front of the probe, if not, the restrictor is there. Enlarging the PP hole or make it double will do nothing (or little) if you do not take out the main restrictor.

Porting in 0.22 will lead to 40-50 more fps

Porting in 0.25 will lead to 20-30 more fps

Porting in 0.30 will lead to 5-10 more fps

 

[heavy-impact]

@ ... and add a 4 gram hammer weight above 145 bar. Lube your slugs with silicone oil.

 

[mrdirect]

@ ... and add a 4 gram hammer weight above 145 bar. Lube your slugs with silicone oil.

Lubing might be it, because I already have Edosan's power kit installed. (Hammer weight, bigger valve)

I have not yet installed the delrin bumper, because I forgot and did not want to open my impact again.

I also have the high pressure huma regulator and it is now on 170 BAR. And this 170 BAR gives me just 900 fps with the Nielsen 39 grain slug, in the 700mm slugliner.

With the .30 caliber installed I get 940 fps with a 44.75 grain pellet, but on 150 BAR.

So lubing might be a reason and also the 'O' at the end of the pellet probe. I have only enlarged it, just like Ernest showed yesterday (he kept the 'O' as well )



https://www.youtube.com/watch?v=RsBcwKqQmdQ



*edit: Have you guys seen the FX Wildcat MKII pellet probe? Looks just the same as when you mod it.

https://www.europeairguns.com/en/optica-2/visores/fx19578

 

[edosan]

I disagree with 1 or 2 things with ER (of thousands we agree on), and that is one of those...I have tested both and removing the O will give you the best airflow, learn how the flow goes and do the exercise. 

In the only cal where the top of the PP (the "O" I mean) is not needed to be removed (But I do it anyway) is in 0.30 cal, since the gain is not really much the open is max at about 7mm (if I recall correct).

Also can you post a pic of your brass port mod?

 

[mrdirect]

Lubing didn't help. Same speed.

I have tested the 33.95 grain .25 pellets and they do 965 fps. (on the 170 BAR in the 700mm slug liner)

So a lot of speed loss when I only get 6 more grains.
25.4 grain pellet:-> 1066 fps (through the sound barrier almost ;-) )
33.95 grain pellet -> 965 fps
39.00 grain slug -> 900 fps

Big difference I think ?

These are the slugs I have:

 

[edosan]

Pellets and slugs are totally different, IME they have about 5gn difference, meaning that a 34gn pellets speed will be about the same than a 29gn slug speed (not exactly, just to have an idea). Something about the Flat Base and size probably.

25.4 grain pellet:-> 1066 fps (through the sound barrier almost )
33.95 grain pellet -> 965 fps
39.00 grain slug -> 900 fps

in 8.55 grains you have 99 fps difference on pellets only, so looks good on 39gn slug

 

[mrdirect]

Okay, so I was worried for nothing? I found 900 so slow after getting used to 940 fps with my .30 pellets. I was expecting more velocity from a lighter weight slug. But hey, I have never even shot these slugs before, I have used up more than 100 just over the chronograph, but I never was outside with them.

Tonight I go to the range, and I can see what the slugs will do on 50 and 100 meters. (54 and 109 yards).
At least when they have room, the place is always fully packed with other shooters.

 

[edosan]

Okay, so I was worried for nothing? I found 900 so slow after getting used to 940 fps with my .30 pellets. I was expecting more velocity from a lighter weight slug. But hey, I have never even shot these slugs before, I have used up more than 100 just over the chronograph, but I never was outside with them.

Tonight I go to the range, and I can see what the slugs will do on 50 and 100 meters. (54 and 109 yards).
At least when they have room, the place is always fully packed with other shooters.

At the end, the ports and liner itself is the big restictor so lower the cal, bigger the restrictor for the air. That is why you see better speeds in higher cals sometimes.

 

[heavy-impact]

@mrdirect The smaller the bore the less area you have for the pressure to act on. Here's a quick and dirty effective psi calculation for .22, .25 and .30

I use .7857 instead of π r ²

.217 x .7857 x 2205psi = 375.9

.25 x .7857 x 2205psi = 433.1

.30 x .7857 x 2205psi = 519.7

 

[2fast2furious]

I disagree with 1 or 2 things with ER (of thousands we agree on), and that is one of those...I have tested both and removing the O will give you the best airflow, learn how the flow goes and do the exercise. 

In the only cal where the top of the PP is not needed to be removed (But I do it anyway) is in 0.30 cal, since the gain is not really much the open is max at about 7mm (if I recall correct).

Also can you post a pic of your brass port mod?

So removing the O on the probe will give more fps? You mentioned removing also the top of the probe. Is that needed? So then the probe would be something like this? ( )

 

[heavy-impact]

So removing the O on the probe will give more fps? You mentioned removing also the top of the probe. Is that needed? So then the probe would be something like this? ( )

Like this...

 

[edosan]

So removing the O on the probe will give more fps? You mentioned removing also the top of the probe. Is that needed? So then the probe would be something like this? ( )

yup, top of the probe is the same than the O (I am referring to the same, depend on the POV) any shape that remove the O will do it ( ) will, or the Heavy shape or the one I show on youtube. Many roads leads to the same place!

PS: I find very VERY annoying that each time I press submit, I go to page 1! ... I understand the disclaimer is important ... still ...