Does anybody know? Is it ok if o ring can be visible like this i the groove?

 

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.

 

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.

 

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

 

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

 

 

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?

 

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

 

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.

 

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

 

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 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 😄

 

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

 

With a longer slot you will also lose cylinder volume. While the sorbo will reduce the volume, it will also make the gun quieter.

 

First i try to make piston shorter, then we will see what next to do,only i don't understand how yours short piston works but mine short plastic piston won't catch sear with pps cylinder

 

My spring guide has a pretty thin base. Also depending on your spring guide/stopper, there can be a nipple/cut out. I shaved the nipple off all of my spring guides mainly because it can cause latching issues with the Bulltrigger. The sear is moved back but depending on your parts, that could be the latching issues. Try more sorbo for the process of elimination as well.

 

I will investigate why isn't catching tomorrow

 

-I think some bull trigger have the sear slightly further back than a standard trigger.
-The piston o-ring should not catch on the port as it goes past. If it does, use a round file and be careful
-Do not extend the port. You will lose critical air volume and that is more important than the initial acceleration of the piston. You will get more fps with air volume than a fast piston but to maximise your cylinder volume you need to correct length inner barrel for the bb weight you are shooting.

 

Am using 0.43,and have 430mm inner barrel

 

One off topic question, is the stock vsr buckings same for bridged and unbridged barrel? I want to open bridge on my steel barrel so i can use ML buckings, hope that will not make problem if i want to put back stock bucking

 

I will using 0.43,or maybe 0.45 for now..
Just need good spring to get 3.5j or 4j,rapax 3+ lost about 20% strength, need to find strong spring but it's must be shorter than rapax to not lose to much strength over time

 

everyone saying about loosing cylinder volume and in both occasions volume is the same as piston go fare as grove on cylinder then no advantage to go this 1 cm as this will not compress air ( air go off through grove ) in first cm but maybe you get some advantage due to when start compressing piston have some acceleration already

 

but maybe you get some advantage due to when start compressing piston have some acceleration already

That is where the advantage is. The initial speed of the piston.

 

The difference is minimal. I would still just get the 430mm inner barrel.

 

I have 430 mm barrel already, 6.03mm
So that part is ok

 

It should be OK