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.
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.
Quote from: nervoustrigger on January 12, 2022, 04:37:00 PMYikes, 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 Wonder why the efficiency is so low, even with mods.
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).
Quote from: cilami on January 12, 2022, 08:49:11 PMThanks 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.
Quote from: Thane on January 13, 2022, 03:57:16 PMQuote from: cilami on January 12, 2022, 08:49:11 PMThanks 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.
Quote from: cilami on January 13, 2022, 07:18:15 PMQuote from: Thane on January 13, 2022, 03:57:16 PMQuote from: cilami on January 12, 2022, 08:49:11 PMThanks 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/8969T86?/They will need shortening but the wire size & diameter are within reasonable tolerance, I think.Hope this helpsEd
Member Joop (AGN) did some cutting of the hammer spring and got this:https://www.airgunnation.com/topic/pp750-hammer-spring-help/#post-1169502By 0.5 mm he meant 0.5 cm.
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: 10.8Shorter HS tune: avg. velocity: 670.3 fps e.s.: 20 fps s.d.: 9.4 N:32 shots HS: 53 mm Avg. FPE: 10.3And 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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