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Old 04-03-2020, 12:30 AM   #1
Vsr10   Vsr10 is offline
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A watching this action army 45 piston and something cross on my mind, my old plastic piston is a bit shorter than a new pps one,groove on stock cylinder is longer, when bolt is pulled back, and sear catches the piston, o ring is visible, so piston have time to accelerate before compression, because pps piston is longer, when sear catches him, o ring is about few mm inside the cylinder, passing groove, so compression start right after trigger being pulled.
Now question of the 40e,is it possible to to gain more fps if i shorten the steel part of the pps piston, enough to o ring be moved more to the spring guide like on the stock one and the Action army one, spring will be more compressed and fps will be higher, but my concern is the o ring, will it tear faster because he will catches end of groove?
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Last edited by Vsr10; 04-03-2020 at 01:19 PM.
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Old 04-04-2020, 02:01 PM   #2
Vsr10   Vsr10 is offline
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Does anybody know? Is it ok if o ring can be visible like this i the groove?
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Old 04-04-2020, 03:34 PM   #3
1tonne   1tonne is offline
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It is better to have the shorter piston. It will give you more cylinder volume which will give you more energy. So, it you are able to shorten the PPS piston, then it would be advisable. You can most likely shorten it by an extra 3mm from the stock one. But you would have to double check that with your trigger system as it may not catch.


The one advantage the longer PPS piston has is that it would be better at joule creep but going off the fact you have a 45 degree trigger, I am guessing your system is not a joule creep one. So I would shorten it.
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Old 04-04-2020, 05:34 PM   #4
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Ah op, perfect timing. I did the testing long vs short piston. As there are many variables, I’ll include some build specs. The results surprised me a little;

In a nutshell with a .48:
Short piston-345fps
Long piston-256fps

More details: Rifle setup:
EdGi 370mm 6.00 barrel
BullTrigg (slight fps boost)
1x Black sorbo pad
AA hop chamber
ML 60 diamond w/ omega
Used EdGi 500fps spring

Short EdGi piston
100mm long
Weighs 35.8g
Set hop for .48-345fps
Dropped in .20-514fps
Turned hop off .20-427fps

Long EdGi piston
116mm long
Weighs 39.5g
Set hop for .48-256fps
Dropped in .20-384fps
Turned hop off .20-351fps

The air seal was perfect at the cylinder head and end of barrel with each piston. I was surprised at how low the output was witch the long piston. But the barrel is 370mm and it doesn't have as much time to speed up. Rifle was noticeably more quiet with the long piston too, due to not moving as fast, as well as hitting the cylinder head/sorbo slower.
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Last edited by Blind Sniper; 04-04-2020 at 05:39 PM.
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Old 04-04-2020, 05:46 PM   #5
Vsr10   Vsr10 is offline
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Quote:
Originally Posted by Blind Sniper View Post
Ah op, perfect timing. I did the testing long vs short piston. As there are many variables, I’ll include some build specs. The results surprised me a little;

In a nutshell with a .48:
Short piston-345fps
Long piston-256fps

More details: Rifle setup:
EdGi 370mm 6.00 barrel
BullTrigg (alight fps boost)
1x Black sorbo pad
AA hop chamber
ML 60 diamond w/ omega
Used EdGi 500fps spring

Short EdGi piston
100mm long
Weighs 35.8g
Set hop for .48-345fps
Dropped in .20-514fps
Turned hop off .20-427fps

Long EdGi piston
116mm long
Weighs 39.5g
Set hop for .48-256fps
Dropped in .20-384fps
Turned hop off .20-351fps

The air seal was perfect at the cylinder head and end of barrel with each piston. I was surprised at how low the output was witch the long piston. But the barrel is 370mm and it doesn't have as much time to speed up. Rifle was noticeably more quiet with the long piston too, due to not moving as fast, as well as hitting the cylinder head/sorbo slower.
Woow, almost 100fps diference
Do you maybe have face to face picture of shorten and longer piston?
I can shorten it, my frend will make me shorter piston end, just only concern is that O ring will be visible and that groove will tear it apart
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Old 04-04-2020, 05:51 PM   #6
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I making my own 90 trigger because price is ridiculous for that part,
I want to shorten the pps piston because with rapax 3+ i only getting 500fps, stock plastic one gets me about 510 fps, but that piston is a bit shorther and have probably more acceleration before starting to compress air inside the cylinder
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Old 04-04-2020, 06:41 PM   #7
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Old 04-05-2020, 01:27 AM   #8
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Originally Posted by Blind Sniper View Post
Nice diference, is the piston head of shorted piston visible in the groove when is bolt pulled back? Like the O ring of my stock piston?
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Old 04-05-2020, 02:33 AM   #9
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No idea, I will have to check. Idk if I can see a lot on the bottom of my receiver.
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Old 04-05-2020, 02:40 AM   #10
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I forgot to take the sear slot into account...
If the shorter piston‘s cup appears in the sear slot, which it probably will, especially since you‘re using a bulltrigger, it will indeed give you higher fps, since the piston can‘t compress any volume, until it’s cup passed the sear slot. Therefore the bb will stay in place at first. Once the piston compresses the cylinder volume, and the bb starts moving, the piston will have a higher velocity, since it had more time to accelerate without moving the bb. This means that the bb will have a higher velocity as well.
A nearly 100fps increase is very impressive!

If the piston cup wouldn’t be visible in the sear slot, I’d still say, the stuff I wrote in the other thread is true though.
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Old 04-05-2020, 04:28 AM   #11
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Quote:
Originally Posted by Blind Sniper View Post
No idea, I will have to check. Idk if I can see a lot on the bottom of my receiver.
You can make mark through the groove on piston and cylinder when bolt is pulled back, when stock is removed , and later when you do a cleaning, you can put piston in cylinder without spring, align it with mark you made and see is it piston head visible and how much,will appreciate if you can make picture of that case, also it is good to know how much is the distance from start of the groove and end of piston, like on the picture beneath, this info is because if i put shorter plastic piston in pps cylinder it won't catch it, because groove lenght isn't same on stock and pps, need this info to know how much i can make short the pps piston
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Old 04-05-2020, 05:14 AM   #12
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Quote:
Originally Posted by Fynn64 View Post
I forgot to take the sear slot into account...
If the shorter piston‘s cup appears in the sear slot, which it probably will, especially since you‘re using a bulltrigger, it will indeed give you higher fps, since the piston can‘t compress any volume, until it’s cup passed the sear slot. Therefore the bb will stay in place at first. Once the piston compresses the cylinder volume, and the bb starts moving, the piston will have a higher velocity, since it had more time to accelerate without moving the bb. This means that the bb will have a higher velocity as well.
A nearly 100fps increase is very impressive!
That is the case with stock cylinder,i want to make same principle on pps, since O ring isnt visible when the bolt is pulled back, there's another question, pps groove is a bit shorther than a pps, so i rather make pps piston shorter than widening the groove and lose cylinder volume..

Will be good i someone can tell what brand cylinder they have and mesure distance on the picture in mm, from start the cylinder, without cyl head, to the start of the groove
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Old 04-05-2020, 12:20 PM   #13
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I always wondered about having an even SHORTER piston but realized the slot in the cylinder and latching etc. However, if it is too short to latch, you can always add material to the cylinder head in order to have it reach the sear, and shorten the spring guide. Sorbo or other material may reduce cylinder volume, BUT if the piston is speeding up before sealing and moving the bb, MAYBE the loss in volume won’t matter. I’m sure there is a point of return like everything else. I want to experiment more though. Downsides I can think of would be more noise, and longer bolt pull.
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Old 04-05-2020, 01:16 PM   #14
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Originally Posted by Blind Sniper View Post
I always wondered about having an even SHORTER piston but realized the slot in the cylinder and latching etc. However, if it is too short to latch, you can always add material to the cylinder head in order to have it reach the sear, and shorten the spring guide. Sorbo or other material may reduce cylinder volume, BUT if the piston is speeding up before sealing and moving the bb, MAYBE the loss in volume won’t matter. I’m sure there is a point of return like everything else. I want to experiment more though. Downsides I can think of would be more noise, and longer bolt pull.
I rather be making a longer groove than add sorbo to the piston and lose cylinder volume where is most important, but if yours piston is already shorter and works great , groove must be already long enough, what cylinder you have?
I can deal 1cm longer bolt pull if that will give me enough fps boost 😄

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Old 04-05-2020, 01:36 PM   #15
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A longer groove won’t change the physical distance you need to latch the piston to the sear. Unless you just mean porting the cylinder. Which is already done, which could actually be the same thing as a shorter piston with extra sorbo. The speed and volume characteristics may be different. Won’t know until you try.

You could also move the trigger box if you tap some new holes. But again, you might be doing a bunch of work to move the variables and see the same results. The fun is in the experimenting though
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