A valve I knocked up this afternoon
Well guys, I was originally using a modified talon valve with an 18″ barrel and was getting the 15.9 grain JSB’s up to about 950 fps. I was looking for a little more so I could shoot the kodiaks at a reasonable velocity.
I reamed out the brass threaded stem surround to just under the seat diameter and made a high flow valve to fit.
The ID of the valve is 4mm and not sure of the OD.
Two flats were milled on each side to expose the ports.
With the tank pumped to 3000 psi, I was getting consistant hight 800’s.
Dry fired a bunch of times and got 980 fps
Dry fired a few more times and got 1020, took a few more shots over the chrono and got 1021, 1025, 1032
Fired off a few more and got 1070, then after about 2 more shots I got 1086
This PSI reading was about 2400 psi
I plan on doing a full string tomorow, starting at about 2600
PICS
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Thanks, I think that one advantage that this stem has is that there is less dead space between the valve seal and the pellet, this means that the air released can only expand a small amount before it hits the pellet, meaning it arrives at more pressure than say a blod stem.
I got some kodiaks because the jsb’s were going ss and it uses a bit too much air for my liking ( about 20 shots at 1010 ) but I think it’s because I’m trying to get high numbers from an 18″ barrel.
I’ve got some 18.1 jsb’s on the way and will post results with them
Dave
I drilled the stem out to 5mm which opened up the ports and the stem ID. I then drilled slightly deeper and sanded everything smooth.
Setup the chrony and got 1050 with 16 grains, I then proceded to shootuntil it reached its peak of 1117 fps, then the fps dropped like a stone. Used too much air and the curve wastoo steep for my liking.
I reduced the amount of travel by cutting down the part that fits into the valve seal. Giving me a top hatdistance of about 0.080″ After this, I found out that my bottle collar was loose, tightened that up and was ready to test again
With this new setup I was getting the JSB’s starting at 1020, rising to 1060 and then falling back down to 1020 over more than 30 shots (I stopped taking readings)
Standard deveation was definatley below 15 fps, more likley lower than 10
Well, Looks like it should shoot the kodiaks at just around 1000 fps for 50FPE from an 18″ barrel.
Dave
Well done Dave! that is about the best numbers seen to date!
good job, now enjoy that thing and shoot it a bunch 🙂
Got bored today and decided to furter mod my valve.
I drilled the stem out to 5mm which opened up the ports and the stem ID. I then drilled slightly deeper and sanded everything smooth.
Setup the chrony and got 1050 with 16 grains, I then proceded to shootuntil it reached its peak of 1117 fps, then the fps dropped like a stone. Used too much air and the curve wastoo steep for my liking.
I reduced the amount of travel by cutting down the part that fits into the valve seal. Giving me a top hatdistance of about 0.080″ After this, I found out that my bottle collar was loose, tightened that up and was ready to test again
With this new setup I was getting the JSB’s starting at 1020, rising to 1060 and then falling back down to 1020 over more than 30 shots (I stopped taking readings)
Standard deveation was definatley below 15 fps, more likley lower than 10
Well, Looks like it should shoot the kodiaks at just around 1000 fps for 50FPE from an 18″ barrel.
Dave
Thats a very nice arrangement.
I think I might keep the valve as it is for a little while, But when I end up getting bored, I will drill the stem out to 0.22″ or 5.5mm which will open the ID of the stem and open up the ports some more.
Dave
pics of my stems, with the one on the bottom an old style Condor stem for comparison.
The top stem is my regular one for most shooting that is 5/16″ od with a .220″ i.d. running three angles ports of 0.149″ IIRC at 45 degrees.
Setscrews are for choking the stem for reduced power as required.
Middle stem is for bigbores and is a 1/2″ stem with a 0.375″ id. Running two angled ports of 0.250″ IIRC.
Valve seat is always the same one but the bits shown allow my Vulture to run from 10fpe to 466fpe depending on cal and bullet weight. 5 minute caliber changes easy as pie 🙂
Walter….
On the first two stems I made, the ports were 3 ports arranged like the blodnob style. However Im using a stem with an OD of about 6mm and didnt have a drill bit small enough for the ports. (Other stems were 8mm OD)
I will leave the valve alone, and might knock up another valve for a diffrent bottle for higher speeds.
Without having a mill, all my milling was done using the tip of a modified reamer, holding the stem in the tool holder of my lathe and the reamer in the chuck.
With a 24″ barrel, I would see just over 1100 fps with 15.9 JSB’s and would put the kodiaks at the high 1000’s. hmm…. however 18″ is much more manageable.
Looks like I might have to pick up a tin of kodiaks to see how fast they can shoot. Should be putting me at 980 with them for a healthy 45 FPE
Dave
@voltar….knife edge i agree, and thats what i would end up with when milling the ports in from an angle not 90 degrees like here, but at 27 degrees (per bigbore bobs suggestion)
btw that is a great string….i wouldnt change a bit….unless your going for top power….but those speeds will kill squirrels at 75 yards easy !
yes thats how i judge thing squirrels/distance…totally new kind of measurement….your got 75 s/d LOL
i bet the limiting factor here is those edges…secondly the 4mm
great work
Testing with fill pressures, I found that a hair under 180 bar, I was getting 999 fps which put my right where I want it.
The air used for the string above was 60 bar or 870 psi, quite a bit but I don’t mind.
This is with an 18″ barrel by the way.
Dave
Nice. 2700 fill and maybe slightly lighter hammer or bit less pre-load?
Results are in, ported it a bit, rounded and smoothes all the sharp edges.
Shot from 190BAR/2775 psi Using 15.9 JSB’
The higher numbers I was seeing last night were false, prorably because I was holding the chrony in my hand and was in lower light.
This is a 30 ish shot string, not aiming at anything, just holding the gun and shooting through the chrony (Consistancy in angle to the chrony could have been a little better)
950.5 (Valve lock)
974.1 (Valve lock)
986.2 (Valve lock)
991.9 (Here we go :D)
1000
1012
1006
1030
1014
1021
1021
1027
1020
1022
1014
1029
1028
1039
1031
1033
1021
1025
1021
1017
1020
1019
1015
1010
1009
1008
1004
1000
994.1
996
Consistancy seems really nice to me.
Just thought I might add, The stem has only a 4mm ID which could be opened up to 6mm if I wanted. But for me, the power and consistancy seems really nice and kick my standard valve’s ass
Im a happy chappy 😛
Dave
If’n it was me I would be going for knife edges as opposed to rounded.
Which do you think is ‘cleaner’ Cyg? be cool to have a flow bench to test eh?
port it a bit….vision how the air flows….and round those edges to help ease the transition….should up the power even more !
That is one fine looking valve stem! Polish it up a bit, streamline the porting and you will be knocking out some very healthy numbers!
You may need to limit stroke if you find you get a tank dump or keep the valve spring tension pretty strong. Over 5 pounds for sure.
Look forward to numbers.
Good work Dave
Walter….
Thats really what im not sure about, seems a bit rough and ready to me 😀 However, I suppose that is the way it goes “Artist never likes his own art”
Will be able to tell by tomorow how good it works.
Seems as though it should put the biz mags (Kodiaks) at around 1000 fps
Dave
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Nice job!