GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: cilami on January 12, 2022, 04:26:42 PM
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I received my new Artemis PP750 cal.177 a couple of days ago. Coming from Europe, it is shooting JSB's Exact 8.44 gr. at 745 fps, giving 18 shots from 250 bar to about 120 bar. Nice pistol and very accurate up to about 25 yards. But when I started adjusting the hammer spring…no change in fps, either up or down. So I think I have 3 options to solve this. 1. Increase regulator pressure. 2. Change stock hammer spring with a lighter one and, 3. Shave the part of the trigger stock that keeps the hammer adjusting screw captive, so I can back it up. Not sure which would be the best option to be able to decrease the velocity and gain some range in fps plus probably gain more shots with less noise/ cooking effort.
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Yikes, yes that works out to an efficiency of about 0.36fpe/ci so even for a short-barreled gun that's atrocious. Definitely appears to confirm your suspicions that it has way too much hammer spring.
All your ideas sound viable to try and should indeed improve shot count, reduce the report, and make the trigger pull more favorable.
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My factory first string was 40 shots 700 FPS with 8.64 gr.
Way oversprung. Even with correct spring tension the adjustment screw does not bring much more than 40FPS of range.
I found very different spring lengths in 5 different PP750s.
Adjust the regulator until you are at your maximum desired velocity with the spring adjustment completely backed out (do any porting at this point).
Then start trimming winds until you see a decrease in fps.
Make sure you are still within the operational range of the regulator, your string should be relatively flat. If it falls consistently from shot 1 your regulator is out of range. The whole operational range of the regulator set screw is less than 1/2 turn, easy to miss.
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My factory first string was 40 shots 700 FPS with 8.64 gr.
Way oversprung. Even with correct spring tension the adjustment screw does not bring much more than 40FPS of range.
I found very different spring lengths in 5 different PP750s.
Adjust the regulator until you are at your maximum desired velocity with the spring adjustment completely backed out (do any porting at this point).
Then start trimming winds until you see a decrease in fps.
Make sure you are still within the operational range of the regulator, your string should be relatively flat. If it falls consistently from shot 1 your regulator is out of range. The whole operational range of the regulator set screw is less than 1/2 turn, easy to miss.
Thanks Thane! Just out of curiosity, did the five springs with different lengths have the same width and wire diameter as your stock spring? Do you remember the exact dimensions? I would like to keep my stock spring untouched and experiment with the length of the aftermarket one(s).
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following with great interest
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Me too.
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Thane,
I saw your post (AGN) with the 30 shots at 750 fps with JSB 8.4. That is exactly the tune I want to achieve. Can you tell me the new dimensions of each port you opened? TIA.
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Yikes, yes that works out to an efficiency of about 0.36fpe/ci so even for a short-barreled gun that's atrocious. Definitely appears to confirm your suspicions that it has way too much hammer spring.
All your ideas sound viable to try and should indeed improve shot count, reduce the report, and make the trigger pull more favorable.
Jason,
I did not realize how low the efficiency is. I would need 50 shots, others things being equal, to reach an "acceptable" efficiency of 1 :o
Wonder why the efficiency is so low, even with mods.
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Yikes, yes that works out to an efficiency of about 0.36fpe/ci so even for a short-barreled gun that's atrocious. Definitely appears to confirm your suspicions that it has way too much hammer spring.
All your ideas sound viable to try and should indeed improve shot count, reduce the report, and make the trigger pull more favorable.
Jason,
I did not realize how low the efficiency is. I would need 50 shots, others things being equal, to reach an "acceptable" efficiency of 1 :o
Wonder why the efficiency is so low, even with mods.
Even with this tune by Thane, https://www.airgunnation.com/topic/pp750-tuning-help-request/?referrer=1 (https://www.airgunnation.com/topic/pp750-tuning-help-request/?referrer=1) the efficiency is around 0.88, assuming a 250 bar initial fill.
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It may simply be that it’s belching air long after the pellet has left the barrel. I bet after backing off the hammer spring to the velocity knee, the efficiency will pull up to 1.0fpe/ci or better. For example, my PP700S-A came in at 1.3fpe/ci downtuned to 6.5fpe. Seems like it was around 1.1fpe/ci at the 12fpe power level.
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Thanks Thane! Just out of curiosity, did the five springs with different lengths have the same width and wire diameter as your stock spring? Do you remember the exact dimensions? I would like to keep my stock spring untouched and experiment with the length of the aftermarket one(s).
Same wire and diameters, different lengths.
I do not have the various lengths recorded. My 1st PP750 in 177 had an uncut factory spring, 2nd PP750 in .22 had a cut factory spring out of the box. Cutting the spring is tuning, the factory spring in not anything special or fitted for performance. It needs adjustment or replacement to your needs. Have more than one spring so you can experiment freely.
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For me the .22 pistols are more efficient than the .177.
Out of the box with US 3.5mm port made 1.28 FPE/CU. for 50 580fps shots (spring came trimmed).
Full efficiency tune at 1.76 FPE, 54 shots ES 4% 635 FPS.
The .177 are not as responsive, the low mass and short barrel make for a quick exit, less time to transfer energy.
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Thanks Thane! Just out of curiosity, did the five springs with different lengths have the same width and wire diameter as your stock spring? Do you remember the exact dimensions? I would like to keep my stock spring untouched and experiment with the length of the aftermarket one(s).
Same wire and diameters, different lengths.
I do not have the various lengths recorded. My 1st PP750 in 177 had an uncut factory spring, 2nd PP750 in .22 had a cut factory spring out of the box. Cutting the spring is tuning, the factory spring in not anything special or fitted for performance. It needs adjustment or replacement to your needs. Have more than one spring so you can experiment freely.
I measured my spring. It is 65 mm L x 9 mm W x 1.12 mm wire dia. For the past two hours I have been searching online for a suitable replacement(s) to play with. No luck so far. I wrote Wes, so fingers crossed...Thanks for the info.
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Thanks Thane! Just out of curiosity, did the five springs with different lengths have the same width and wire diameter as your stock spring? Do you remember the exact dimensions? I would like to keep my stock spring untouched and experiment with the length of the aftermarket one(s).
Same wire and diameters, different lengths.
I do not have the various lengths recorded. My 1st PP750 in 177 had an uncut factory spring, 2nd PP750 in .22 had a cut factory spring out of the box. Cutting the spring is tuning, the factory spring in not anything special or fitted for performance. It needs adjustment or replacement to your needs. Have more than one spring so you can experiment freely.
I measured my spring. It is 65 mm L x 9 mm W x 1.12 mm wire dia. For the past two hours I have been searching online for a suitable replacement(s) to play with. No luck so far. I wrote Wes, so fingers crossed...Thanks for the info.
Here' are 2 at McMaster-Carr that are very close to the dimensions you seek
https://www.mcmaster.com/94125K207/ (https://www.mcmaster.com/94125K207/)
https://www.mcmaster.com/8969T86?/ (https://www.mcmaster.com/8969T86?/)
They will need shortening but the wire size & diameter are within reasonable tolerance, I think.
Hope this helps
Ed
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Thanks Thane! Just out of curiosity, did the five springs with different lengths have the same width and wire diameter as your stock spring? Do you remember the exact dimensions? I would like to keep my stock spring untouched and experiment with the length of the aftermarket one(s).
Same wire and diameters, different lengths.
I do not have the various lengths recorded. My 1st PP750 in 177 had an uncut factory spring, 2nd PP750 in .22 had a cut factory spring out of the box. Cutting the spring is tuning, the factory spring in not anything special or fitted for performance. It needs adjustment or replacement to your needs. Have more than one spring so you can experiment freely.
I measured my spring. It is 65 mm L x 9 mm W x 1.12 mm wire dia. For the past two hours I have been searching online for a suitable replacement(s) to play with. No luck so far. I wrote Wes, so fingers crossed...Thanks for the info.
Here' are 2 at McMaster-Carr that are very close to the dimensions you seek
https://www.mcmaster.com/94125K207/ (https://www.mcmaster.com/94125K207/)
https://www.mcmaster.com/8969T86?/ (https://www.mcmaster.com/8969T86?/)
They will need shortening but the wire size & diameter are within reasonable tolerance, I think.
Hope this helps
Ed
Thanks Ed!
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[
[/quote]
I measured my spring. It is 65 mm L x 9 mm W x 1.12 mm wire dia. For the past two hours I have been searching online for a suitable replacement(s) to play with. No luck so far. I wrote Wes, so fingers crossed...Thanks for the info.
[/quote]
Here' are 2 at McMaster-Carr that are very close to the dimensions you seek
https://www.mcmaster.com/94125K207/ (https://www.mcmaster.com/94125K207/)
https://www.mcmaster.com/8969T86?/ (https://www.mcmaster.com/8969T86?/)
They will need shortening but the wire size & diameter are within reasonable tolerance, I think.
Hope this helps
Ed
[/quote]
Thanks Ed!
[/quote]
My pleasure, Cilami
Please let us know how they work out
Ed
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Member Joop (AGN) did some cutting of the hammer spring and got this:
https://www.airgunnation.com/topic/pp750-hammer-spring-help/#post-1169502 (https://www.airgunnation.com/topic/pp750-hammer-spring-help/#post-1169502)
By 0.5 mm he meant 0.5 cm.
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Member Joop (AGN) did some cutting of the hammer spring and got this:
https://www.airgunnation.com/topic/pp750-hammer-spring-help/#post-1169502 (https://www.airgunnation.com/topic/pp750-hammer-spring-help/#post-1169502)
By 0.5 mm he meant 0.5 cm.
Wow! This is my next step with my pp750 that is right where Joop started. His 6cm chrony readings are very similar to what I have been getting.
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I received a spare hammer spring from Wes from AAF in Canada (fantastic customer service, btw). After removing 12 mm to the stock hammer spring (from 65 mm to 53 mm), this is what I got with JSB Hades, 10.34 gr., no other changes:
Stock tune: avg. velocity: 686.2 fps
e.s.:19 fps
s.d.: 5.05
N:17 shots
Stock HS: 65 mm
Avg. FPE: 10.8
Shorter HS tune: avg. velocity: 670.3 fps
e.s.: 20 fps
s.d.: 9.4
N:32 shots
HS: 53 mm
Avg. FPE: 10.3
And now I can adjust the fps from 686 fps to 400 or less, if needed. Less noise and less cocking effort. With the DonnyFl Tanto...shhh!. Great for iguanas at <25 yds. with good shot placement. And the accuracy is there!
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I received a spare hammer spring from Wes from AAF in Canada (fantastic customer service, btw). After removing 12 mm to the stock hammer spring (from 65 mm to 53 mm), this is what I got with JSB Hades, 10.34 gr., no other changes:
Stock tune: avg. velocity: 686.2 fps
e.s.:19 fps
s.d.: 5.05
N:17 shots
Stock HS: 65 mm
Avg. FPE: 10.8
Shorter HS tune: avg. velocity: 670.3 fps
e.s.: 20 fps
s.d.: 9.4
N:32 shots
HS: 53 mm
Avg. FPE: 10.3
And now I can adjust the fps from 686 fps to 400 or less, if needed. Less noise and less cocking effort. With the DonnyFl Tanto...shhh!. Great for iguanas at <25 yds. with good shot placement. And the accuracy is there!
I calculated the efficiency (from 245 to 110 bar) and got 0.68 FPE/c.i. per shot. Room to improve... ::)