More preload = lower FPE?

[Perazzi mx8]

Wanted to bump up FPE on my HW97. The gun was pro tuned to <12 FPE at my request and shoots 8.4s very well but I wanted to experiment with >12fpe and 10.34s. I have some delrin spacer washers which I added 1 at a time and chrono’d after each addition. To my surprise every time I added a spacer to increase preload I saw a slight DECREASE in FPS!  Any ideas as to what is happening here?

[Mark 611]

Ya to heavy of a pellet for that power plant! and yes u can space it up to much! to where the spring will not use its energy! it called chocking the spring! the heavier the pellet the more it needs to use the relaxed spring length to achieve max velocity! also using to small of a spring wire will kill ur power! a 10.5gn pellet needs a 128 wire spring + the correct swept volume to get the best results! JMO

[nced]

Wanted to bump up FPE on my HW97. The gun was pro tuned to <12 FPE at my request and shoots 8.4s very well but I wanted to experiment with >12fpe and 10.34s. I have some delrin spacer washers which I added 1 at a time and chrono’d after each addition. To my surprise every time I added a spacer to increase preload I saw a slight DECREASE in FPS!  Any ideas as to what is happening here?

Springers are all about timing! Too much preload can cause the pellet to start moving in the leade before peak pressure has built up. When living in West Virginia I was trying to get 800fps with 10.5 grain pellets from my Beeman R10 springer using a heavy wire Maccari steelgate spring (think .142 wire) and "fully spaced up" (one added washer caused coil bind) the highest velocity I got was 780fps with 10.5s (tad over 14fpe). Well, after a shooting session I accidentally put the gun away COCKED for two days. The next time I shot the gun I noticed the "goof up" and shot the pellet away. When I re-cocked the gun I noticed that the cocking effort was noticeably less and I shot a 10.5 grain pellet over the chrony sensors and was surprised that the readout was 790fps (14.5ish fps) with the sagged spring. Obviously the gun was "over sprung", even after the "two day sag".

Anywho.....springer balancing is rather complicated and it's a function of pellet weight, spring coil size and count (the velocity of the expanding spring expanding has weight), spring preload, yada, yada, yada !

[SpiralGroove]

Anywho.....springer balancing is rather complicated and it's a function of pellet weight, spring coil size and count (the velocity of the expanding spring expanding has weight), spring preload, yada, yada, yada !

Yeah, I've cut 2 coils off springs many times to get a smoother shot cycle, only to find out velocity usually remains the same .   

[Yogi]

Wanted to bump up FPE on my HW97. The gun was pro tuned to <12 FPE at my request and shoots 8.4s very well but I wanted to experiment with >12fpe and 10.34s. I have some delrin spacer washers which I added 1 at a time and chrono’d after each addition. To my surprise every time I added a spacer to increase preload I saw a slight DECREASE in FPS!  Any ideas as to what is happening here?

What spring is in it?  You said "pro-tuned".  Did they change the factory spring?  The factory spring plus a spacer should get you over 12fpe.

-Y

[Motorhead]

One of my tune jobs ... Was a coil cut OEM spring reducing preload and allowing power to soften up without getting piston bounce from a lessor spring rate.
When OP had asked if he could power back up, Had suggested trying some preload to see what would happen, stating if power don't come up or spring goes into coil bind a fresh full length spring would be required.

Scott S