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.
Tuning PP750 hammer spring help
- Thread starter cilami
- Start date
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.
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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I'd be happy with 745fps. I've done all kinds of mods to mine and have only gotten 688fps. This makes me think you're at the upper limit and probably cant get it higher. If you're wanting to slow it down I'd start with the regulator with the hammer spring all the way out. My reg is at 150bar and hammer spring half way in. Too much hammer spring you risk breaking the poppet.
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Yes. I am happy with the 10 fpe I am getting now. Just need to tune to the knee of the curve and call it done. I have the hammer spring all the way out and still have 740 fps. Maybe I am close to the knee?Think will try a lighter spring first.
Don' t want to open my pistol yet since I am having a lot of fun with it now. If anyone around here knows the stock spring dimensions, please let me know so I can start looking for a lighter replacement.
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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
Wonder why the efficiency is so low, even with mods.
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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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Hi Cilami,
Look at my topic what i have done with the hammerspring.
I have more than 85 shots a filling from 250/100 bar.
My reg. stands on 120 bar.
Its a peace of cake.
Regards from Joop of the Netherlands
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Look at my topic what i have done with the hammerspring.
I have more than 85 shots a filling from 250/100 bar.
My reg. stands on 120 bar.
Its a peace of cake.
Regards from Joop of the Netherlands
********************************************
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This is what i have done with my hammerspring:
Thanks Joop!
What velocity and shot count you had with the 60 mm spring vs. the 55 mm? Which pellets? You did a great job increasing your shot count.
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The original hammerspring is 6cm long.
With this spring and the reg. on 120 bar i had this shotcount:
Then i have cut of the first 0.5mm of the hammerspring and i have this shotcount:
Then i moved the second 0.5 mm just totaly i moved 1 cm of the hammerspring.
This is this shotcount:
In all this counts the hammerspringscrew is completly turnt out.
The pellets i use are the JSB Express 0.51 gr and i have a good 10.5 joules
This is at 10m
Regards Joop
With this spring and the reg. on 120 bar i had this shotcount:
Then i have cut of the first 0.5mm of the hammerspring and i have this shotcount:
Then i moved the second 0.5 mm just totaly i moved 1 cm of the hammerspring.
This is this shotcount:
In all this counts the hammerspringscrew is completly turnt out.
The pellets i use are the JSB Express 0.51 gr and i have a good 10.5 joules
This is at 10m
Regards Joop
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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.
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.
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