New valve, odd results.
I thought I’d try a variation on the tried and tested design. A shorter stem but overall OD of 10mm (still 6mm bore). This allowed me to put in x4 3mm ports instead of x3 3mm ports (behind the 4.5mm main aperture). x4 matches the 6mm bore for total area. Being behind the 4.5mm I figured the venturi effect would either increase or remain the same.
It turns out I’m getting around 50fps less on the x4. But on two test shots, both the first on a new fill up to 3000psi, I’ve had 1500fps and 1600fps. After that they go down to 1050fps and remain at that thereafter.
I am getting a bit of blowout from the breech area, I think from the nozzle inside the breech-block (it’s a tad slack in the o-ring in there). Could that make a 50fps difference? And how about the 1500 and 1600, are those both chrony glitches? My ears did ring. Or is it somehow possible to get that kind of massive variation?
The next experiment is to increase the main aperture to 5mm.
For information, the hammer is still 150g on a Blod main-spring with a 10mm spacer. The stem-stroke is 5mm but it travels only (approx) 2mm or 3mm (I put a piece of blu-tack under the top-hat at 2mm thickness, it wasn’t touched).
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Eley do a Magnum pellet in .22 which is about 31 grains and is bullet shaped. Wouldn’t this overcome the supersonic destablisation effect??
I’m using a 100 gram hammer and whilst not noticing what you are descibing JFK, there is some pronounced recoil now.
First, I’d like to compliment you on your persistence and determination on this project.
What weight/make of pellet are you using? I’m sure that 150 gr hammer has enough stored energy to open any valve but I would think it would have too much “inertia (?)” and throw your shots off. By that I mean when you release the trigger, you have a 150 gr hammer moving rearward while the (equal but opposite) spring force is pushing the gun forward. Have you felt anything like that? I ask because I have a 100 gr hammer and noticed the difference from the original hammer and weight.
Lastly, what FPS range are you looking to achieve? I thought going trans sonic de-stabilized the pellet?
Keep up the good work and thanks for sharing the results,
John
1150s with the 5mm aperture and 15mm of spacers.
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What weight/make of pellet are you using? I’m sure that 150 gr hammer has enough stored energy to open any valve but I would think it would have too much “inertia (?)” and throw your shots off. By that I mean when you release the trigger, you have a 150 gr hammer moving rearward while the (equal but opposite) spring force is pushing the gun forward. Have you felt anything like that? I ask because I have a 100 gr hammer and noticed the difference from the original hammer and weight.
Lastly, what FPS range are you looking to achieve? I thought going trans sonic de-stabilized the pellet?
Keep up the good work and thanks for sharing the results,
John
Cheers John. 🙂
I’m using 21-grain Bisley Magnums (.22). There is a tiny amount of recoil but not enough to spoil a shot. FPS, I’m looking for as much power as possible so you US chaps can get the best out of your .25 cals. With inter-changeable heads the output can be reduced for other purposes. At least that’s the vague plan. 😆