GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: SDG on March 31, 2022, 02:38:11 PM
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Hello
I was tinkering with the hammer weight of my Artemis PR900W and discovered something interesting.
The reason for this is because i wanted to make it more efficient and above all quieter.
So i made a new hammer and started cutting away at it and testing the result of each incremental weight reduction.
As predicted the velocities started to drop but at higher tank pressures i noticed some erratic results.
Plus it was still loud to my liking.
So i decided to cut some more weight of the hammer. This time i cut the sides of the rear "flange" as illustrated in the below picture.
(http://IMG_20220331_185151.jpg)
The original hammer (black) is 35 grams the lighter one (metal) is 22 grams.
When I tested the lighter one the velocity shot up higher than those with the original hammer.
Which is quite suprising yet explainable.
The rear flange on the original hammer acts as an air piston in the round tube it sits in. When fired this creates an air cushion which slows down the hammer. Reducing the ability of the hammer to knock open the valve. But because of the heavy weight of the hammer the valve is slamed open for a long time. Added to this when the valve starts to close the rearward motion of the hammer possibly creates a underpressure which slows the hammer and the closing of the valve.
This might explain the loud noise and reduced efficiency of these guns since the valve probably closes after the pellet has left the bore.
Next up i will try to reduce the weight of the hammer even further to try to reduce noise and increase efficiency.
If you have any suggestions let me know.
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Reducing hammer weight may give you erratic results at higher pressures, as the hammer is struggling to open the valve. If reducing hammer weight and/or spring preload, it's probably best to reduce fill pressure. You will have to map out your velocity at various pressures, starting at your normal fill pressure and shoot down to whare the velocity drops off beyond what you find an acceptable spread. This should give an idea to the maximum and minimum pressures for your given hammer weight.
Reducing the transfer port diameter is also an option to gain some efficiency, reduce noise and flatten the bell curve (the velocity spread at various pressures). Its possible to gain a long flat shot string, but at a much reduced velocity or just limit the peak velocity and gain a few shots, all depending on the inner diameter of the transfer port. I'm not familiar with your particular rifle, hopefully others will chime in and assist in your inquiries further.
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Interesting, I have a CP1 which uses a similar hammer. I think on mine the tube vents through the slot at the top.
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Interesting, I have a CP1 which uses a similar hammer. I think on mine the tube vents through the slot at the top.
I thought the same. There is a slot on top of the tube where the alan screw of the bolt rides in. It seems the space between the slot and the screw is small enough to cause this effect.
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On my CP1 there was a lot of hammer bounce, wasting CO2. The Bstaley buffer (o-ring) mod or using different (shorter) spring (with different end cap and guide) both increased the efficiency.
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I managed to do a bit more testing.
I decided to cut a lot of material from the hammer to see what it gives instead of going incrementally lower.
In the photo below you can see the lightened hammer. The original hammer was 35 grams, the new one is 15 grams.
Finally with this hammer the velocity dropped by about 100fps. From over 1000fps to a bit over 900fps.
The gun was also a lot quieter and the velocity curve was pretty consistent.
Seemed promissing, a lot more testing to do.
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Any updates? Firewalker has determined the correct size for the o-ring mod and is working on his own lightened hammers. I ordered 50, 25 in Buna 70 and the other half in Buna 90. (14.5x1.5)
I'd love to see what your curve looks like.