Tuning Decreasing Hammer Spring Increased speed???🤔

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djmoe95

djmoe95

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Feb 27, 2024
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I have a pcp that shoot great with 18.3gr pellets. Less than 2/3 of an inch at 55 yards with pellets. But the projectiles I wanna shoot are slugs. Not high gr ones but 20-23gr ones because I don't wanna be shooting a motor with my 20-37ft-lb gun(no matter how I mod it, I don't get more than that and I gave up). As I was tuning for shooting slugs, I found out that my gun doesn't like shooting those slugs at high speed. So, I tried to find the highest speed I can get without getting grouping more than 2 inches at 50 yards. While I was tuning, I found out that at 1800 psi regulator set point and up, decreasing Hammer Spring results in increased speed. I found that out because I have the hammer spring tension highest while adjusting the regulator then reduce the hammer spring little by little for each regulator set point. As far as I know, normally, shouldn't the speed decrease with the hammer spring tension decrease?
I've been pondering on this one for like a week now and couldn't figure it out. So, I posted here hoping that someone would have an answer to that.

My gun specs.
18 inch 1:16 left twist barrel in 22 cal.
1800 psi is mostly the pressure I set on reg.
The air out hole on valve, I think called port, was 4.5mm but I drilled it to be 6mm.
Transfer way (the part on action block that connect the port to the transfer port behind the barrel is around 4.3mm and I cannot find a way to increase it because the hole is unreachable with a drill.
The brass transfer port is the kind with two elongated holes with a bridge between them. Total dimension of the holes should be around 6-7mm.
Using probe with small pin that push the pellets/slugs in. (Slug probe??)
My hammer has short stiff spring that reaches its normal state 6-8mm before the hammer hit the valve. I've recorded the hammer in action in slow motion and I don't see hammer bouncing between spring and valve.
 
Take a body of water like a swimming pool, slap the surface as hard as you can. Now do the same thing slower.
Your gun is relying on valve dwell. You’ll notice the same effect. Most times this is due to the engineered hammer weight for your gun being to light. It’s opening yes but the kinetic energy is actually being absorbed more trying to initially open the valve.
Low hammer weight to higher valve pressure.
 
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If your hammer spring setting is way above where you hit max fps with it it can cause it to be lower. I have seen it myself. Say at 1800psi your max fps is at 3 turns in on HS setting buy your gun allows 6 HS turns. I've seen lower fps at 6 turns than the max that occurs at 3. Why that happens I'm not 100% sure but is that what your meaning?
 
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“ I found that out because I have the hammer spring tension highest while adjusting the regulator then reduce the hammer spring little by little for each regulator set point.”

This makes it confusing for me. Generally speaking, only one thing is adjusted at a time to see different results. The increase in velocity could be just a result of the pressure change.

What brand/model rifle?

Dave
 
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Airgun-Revisions, I thought so too. I tried using longer poppet pin. Which I assume would results in the longer dwelling of the valve and saw that the valve did dwell because the 0.3L @3000 PSI bottle got used up within 1 and a half 15 rounds mag. And also my gun sound changed from snap sound to way louder woosh sound which I assume is because of waste air after the projectile left the barrel. So, I concluded myself that dwell is not the problem here. As far as I know, after the projectile left the barrel, no matter if the valve is still open (dwelling) after the projectile left the barrel, it's just waste air.

Hi, Dairyboy, I think we're on the same page. I don't know if that strange phenomenon only occur to us or something.
 
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If you do not adjust the reg
And
You adjust hammer spring higher
And
Your velocity drops


You could be bottoming something out (hammer or valve poppet) which causes the hammer/poppet to close much quicker. Could be a possibility. And it obviously sounds as though it’s at the point of over dwelling with the way you describe.

Dave
 
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sb327 said:
“ I found that out because I have the hammer spring tension highest while adjusting the regulator then reduce the hammer spring little by little for each regulator set point.”

This makes it confusing for me. Generally speaking, only one thing is adjusted at a time to see different results. The increase in velocity could be just a result of the pressure change.

What brand/model rifle?

Dave
Click to expand...
Sorry if my English is bad. Not my native language. So, sorry about that. Let me explain a bit. For example, I set the regulator pressure to 1500 PSI with the hammer spring adjuster at highest. Shoot a 10 rounds while reducing the hammer spring adjuster a little every 2 rounds. Then repeat with 1600 PSI regulator pressure 10 rounds.
The point of doing that is looking for power similarities (for example highest hammer spring tension at 1300 PSI regulator pressure might have the same or similar power with lowest hammer spring tension at 2000 PSI regulator pressure.) and sound difference or probably efficiency (bad long dwell waste air, produce more noice while some high regulator pressure and correct spring tension makes less dwell while keeping just enough air to push projectile, less air wasted, thus less noice).

My gun is not a branded one. An CAD file I found on Grabcad inspired and brought into reality using after market parts mainly barrel and Z valve and more than a dozen visit to machine shop. So, I implemented all the ideas I've read online about getting higher adjustable power is somewhat implemented on it. Like bigger port, dual hole transfer port, a regulated Z valve with a plenum of about or more than 10cc, adjustable spring tension, etc.
 
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djmoe95 said:
Sorry if my English is bad. Not my native language. So, sorry about that. Let me explain a bit. For example, I set the regulator pressure to 1500 PSI with the hammer spring adjuster at highest. Shoot a 10 rounds while reducing the hammer spring adjuster a little every 2 rounds. Then repeat with 1600 PSI regulator pressure 10 rounds.
The point of doing that is looking for power similarities (for example highest hammer spring tension at 1300 PSI regulator pressure might have the same or similar power with lowest hammer spring tension at 2000 PSI regulator pressure.) and sound difference or probably efficiency (bad long dwell waste air, produce more noice while some high regulator pressure and correct spring tension makes less dwell while keeping just enough air to push projectile, less air wasted, thus less noice).

My gun is not a branded one. An CAD file I found on Grabcad inspired and brought into reality using after market parts mainly barrel and Z valve and more than a dozen visit to machine shop. So, I implemented all the ideas I've read online about getting higher adjustable power is somewhat implemented on it. Like bigger port, dual hole transfer port, a regulated Z valve with a plenum of about or more than 10cc, adjustable spring tension, etc.
Click to expand...
Implementing all the ideas about high power. Yet still failed to get more than 40 ft-lb. ,😅😅
 
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sb327 said:
I really feel your inability to get over 40fpe is due to the transfer path being AND the plenum being only 10cc.

Kudos to you for building your own airgun. I really enjoy these types of guns. Excellent!

Is the transfer path part that you can’t get to 3D printed?

Dave
Click to expand...
I think you meant transfer path too small? Yes, It is small because I drilled the transfer path and the screw hole that is used to keep the brass transfer port in place using one drill size. The screw is M5. So, I think I used 4.3mm drill bit for it. It's my fault not using separate parts for the breach and the part that hammer and the valve is in. So that I could drill bigger transfer path from under the upper piece.
3d printing an airgun action block? Feels like creating a bomb that I'll put my cheeks on everyday basic. For me, I can't trust a plastic part to handle 2000-3000 psi for sure.
 
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You're probably getting hammer rebound. It's bottoming on the back face of the valve and bouncing back faster than the HS would be able to. I've heard it called over driving the hammer. I had that problem with one of my Pcps and I just put a Oring in the hammer bore to cushion it.

Add weight to the hammer will increase the dwell but as has already been stated if the air is still coming out of the muzzle it's not going to increase power cause Elvis has left the building.😁
 
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djmoe95 said:
I think you meant transfer path too small? Yes, It is small because I drilled the transfer path and the screw hole that is used to keep the brass transfer port in place using one drill size. The screw is M5. So, I think I used 4.3mm drill bit for it. It's my fault not using separate parts for the breach and the part that hammer and the valve is in. So that I could drill bigger transfer path from under the upper piece.
3d printing an airgun action block? Feels like creating a bomb that I'll put my cheeks on everyday basic. For me, I can't trust a plastic part to handle 2000-3000 psi for sure.
Click to expand...
Oh heck, it'll be fine, the 3D printed block, do you have a good plastic surgeon? <---American humor Plastic has a place and it's nowhere near high pressure or heat. That said....with the right plastic/carbon reinforced it MIGHT work but I'd test the daylights out if it from a long way off and I still wouldn't trust it.
 
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djmoe95 said:
I think you meant transfer path too small? Yes, It is small because I drilled the transfer path and the screw hole that is used to keep the brass transfer port in place using one drill size. The screw is M5. So, I think I used 4.3mm drill bit for it. It's my fault not using separate parts for the breach and the part that hammer and the valve is in. So that I could drill bigger transfer path from under the upper piece.
3d printing an airgun action block? Feels like creating a bomb that I'll put my cheeks on everyday basic. For me, I can't trust a plastic part to handle 2000-3000 psi for sure.
Click to expand...
Can you step up to the next screw size? I recently did this with a notos to open the transfer path.

Fwiw, I was not suggesting to 3D print an action block or other pressure vessel. I just have no idea how your system is put together.

Dave
 
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Dairyboy said:
If your hammer spring setting is way above where you hit max fps with it it can cause it to be lower. I have seen it myself. Say at 1800psi your max fps is at 3 turns in on HS setting buy your gun allows 6 HS turns. I've seen lower fps at 6 turns than the max that occurs at 3. Why that happens I'm not 100% sure but is that what your meaning?
Click to expand...

I agree it's way over the peak on the hammer setting .Keep lowering it to find the max fps. Then back off a bit .
 
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I figured out the problem. As the Desertsilver said the valve poppet bottom out and hammer got bounced back faster by the face of the valve. Fixed it using a round polyurethane rod cut and drilled in the center. That thing is a bit soft to bounce the hammer back. Can also make a bit of dwell because it takes a bit of time to absorb the hammer hit fully. Just need the right thickness to have the poppet moves backwards significantly.

sb327, I figured that next screw size would be m6 and need at least 5mm of hole to thread it. But I was afraid that the bigger hole might make it not air tight. So, I am looking for a Dremel bit with small head and shaft that I can somehow thread into the hole on top and grind to enlarge the transfer path. Before trying out with Dremel, I don't wanna step up the screw size yet because the aluminium has easy tendency of thread stripping and the anodize hardened threads that I currently have ensure not stripping threads easily. If I make new thread with a bigger hole, anodized area will be gone and it's hard or nearly impossible to anodize just that area alone.

Anyways, My problem in the title of this thread has been solved. So, it's a win for me. And thanks for all the ppl who helped.
 
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