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PostPosted: Fri Nov 13, 2020 1:34 am 

Joined: Thu Jun 11, 2020 1:42 am
Posts: 17
Hello.i am wondering i had a 1000 fps put in my rifle but it was two loud and recoil to much. So i went down to a 800fps it still seems loud ect. I still have the 100ffps piston in it. Would changung the piston back to the stock helpy problem?iam wondering what effects different nprmal piston have.oh ya my rifles a phantom thanks

PostPosted: Fri Nov 13, 2020 7:11 am 

Joined: Mon May 26, 2014 1:08 am
Posts: 566
Location: Thunder Bay

Check out Todd Cooper's posts and links in the recent thread above. He explains the differences in piston lengths, springs, and preload variables in the search for a rifle's "sweet spot".

12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

Too soon old too late smart.

PostPosted: Fri Nov 13, 2020 12:29 pm 
Site Moderator

Joined: Sat Sep 03, 2005 9:25 am
Posts: 3608
Location: Ontario, Canada
My Optimus with 150mm piston is detuned to 750-800fps. To get this power level I used the 36 coil (.122" wire) mainspring known as the 4D spring. The long 1.5" factory spacer was replaced with a 3/8" spacer that gives about 3/8" of preload. A stack of washers should work for this if you don't have a machinist friend. It is nice to shoot but louder than the 170mm piston tuned to 625fps.

My Optimus with the 170mm piston shoots around 625fps with the 33 coil (.118" wire) mainspring known as the 4B spring. I have a 3/4" spacer installed to give about 1/4" of preload. The rifle is simple to assemble with this mild spacer. The rifle is calm to shoot and makes a great indoor plinker at the HW30S power level.

If you only have the full power 4D mainspring (36 coils of .122" wire) then you still might be able to make a nice mid-power shooter. Try the longer (and heavier) 170mm piston and space the spring so it only has 1/4" to 3/8" of preload. The stroke will be 20mm shorter than with the 150mm piston. You can compare this to the same spring and preload with the shorter 150mm piston.

Longer pistons decrease the power stroke length and will usually drop your speed. The heavy .122" wire spring might still be a bit harsh but try it anyway. I prefer the milder 4B spring (.118" wire) for a sweet and quiet shooter.

I'm looking forward to reading about your results.

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