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Discussion Starter · #1 · (Edited)
We all want the most out of our rifles. To get this we need to tune the rifles and one way of tuning a rifle is to get the correct weight piston for the spring that you have selected. If done correctly, this will give you the most energy that your system has to offer with that particular spring.

This is how it works:
The most important part of a pistons travel is not at the start but at the end when it hits the cylinder head. This is when the bb should be exiting the barrel and this is when you want your bb to have as much energy as possible. If for some reason, the piston slows down at the end of it's travel, then the bb will not reach it's maximum potential because the piston did not reach it's maximum speed. Now if a piston is too light, it can accelerate really fast but as the pressure builds up in the cylinder, it can start to bounce on this high pressure cushion because it does not have enough inertia to push through the pressure cushion. To fix this you can add some weight to the piston to give it more mass. This will in turn give it more inertia to push through this pressure cushion. So the piston may travel slower as the start but it can finish faster because it does not get stuck on a high pressure cushion of air.
NOTE: There is a point though where if you add too much weight, the piston will start off slow and also end slow.

Here are some examples of how piston weight can affect the piston speed:
Weak Spring + Low Mass Piston = Piston travel finishes fast
Weak Spring + Medium Mass Piston = Piston travel finishes moderate
Weak Spring + High Mass Piston = Piston travel finishes slow
Weak Spring + Extra High Mass Piston= Piston travel finishes very slow
Medium Spring + Low Mass Piston = Piston travel finishes moderate
Medium Spring + Medium Mass Piston = Piston travel finishes fast
Medium Spring + High Mass Piston = Piston travel finishes moderate
Medium Spring + Extra High Mass Piston = Piston travel finishes slow
Strong Spring + Low Mass Piston = Piston travel finishes slow
Strong Spring + Medium Mass Piston = Piston travel finishes moderate
Strong Spring + High Mass Piston = Piston travel finishes fast
Strong Spring + Extra High Mass Piston = Piston travel finishes moderate

As you can see at the very bottom, the extra high mass piston still did not get the best result as it was too heavy. So you can even add too much weight to a strong spring.

Another thing to help stop the pressure cushion from occurring is to make sure that the air nozzle hole is as wide as possible. (But do not make the walls of your air nozzle too thin). Also, you may find that putting in a slightly weaker spring can actually increase the fps of the rifle. This is because the pressure does not build up so much and so the piston can go through it's full travel without hitting a pressure cushion. So not slowing down at the end.

Overall, there is no formula to doing this right as there are too many variables. So experiment.
I normally just wrap electrical solder around the shaft of a bolt action piston and the hold it on with a layer of electrical tape. This lasts a very long time if you wrap the solder tightly around the piston. It is also adjustable and very cheap. I normally like to start with a piston weight of about 30gm and then increase it by 10gm at a time and retest to see if it improved. For a strong spring you may want a weight of about 70-80gm in total.
If you have an AEG you may need to experiment with different pistons and piston heads to get the correct weight. You can also add weights to the inside of the piston but this can also compress your spring a little which in turn can alter the result. For around 1 joule I would suggest around 15-20gm's (This is only an estimation because if the AEG has a short inner barrel, it may have a slightly bigger spring to get the joules rate). At 1.6 joules I would suggest 20-25gm. At 2 joules I would suggest 25-30gm.
 

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Discussion Starter · #3 ·
A lot of this stuff is just stock standard stuff from the Airgun/Pellet gun teching world. They have the same issue with piston bounce on a cushion of air. So good airgun manufactures (not all) will try to get the perfect piston weight. In airsoft a manufacturer will just add a piston and not take not of the best weight for it.
The main difference is that we need a lighter piston as we use weaker springs. But stock pistons are normally too light
 

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The limited testing I've done while building my vsr showed that adding weight to the piston (not much, from 40 to 60 grams or so) did nothing but introduce an easy way to cheat the chrono.
Lower J/ms readings on 0.2s, same exact J on 0.4s with just a hint of variation on 0.3s..
 

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Discussion Starter · #5 ·
Adding weight will make it joule creep easier. That is a natural occurrence.
 

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Discussion Starter · #6 ·
The last build I did, when the piston was too light it only got 2.85 joules with 0.48gm bb's (Aluminium Action Army Piston). Then I added weight to the piston and the energy increased to 3.3 joules. (I didn't actually measure the weight of the piston. Sorry). So it is not a massive amount that you gain but it is still very much worth it.
 

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Oh well, I need to open the gun again this week as I replaced the hop rubber and gained 0.2J going from a 50 to a 70.
I'll dick around a little more with piston weights :D
 
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Few days ago I did a bb energy/fps/piston weights testing.
Platform: TMVSR10 pro
FPS: 530-540fps 0.20gr bb
Inner Barrel: ML C.J 550mm-6.04mm
HopUp Unit: Maple Leaf
HopUp Bucking: ML Mr Hop 70
Spring: Laylax SP150
Piston: Laylax PSS10 High Pressure (40gr)
*Zeroed HopUp
*Chronograph: AC5000
*BBs: 0.48gr BLS

Ammo
Piston Weight (gr)
Velocity (ft/s)
Energy (joules)
0.48gr​
70gr​
357.2​
2.85​
356.5​
2.83​
368.5​
3.03​
365.2​
2.97​
328.6​
2.41​
55.5gr​
367.7​
3.02​
370.2​
3.05​
357.2​
2.85​
371.0​
3.07​
368.5​
3.03​
322.1​
2.31​
47.5gr​
357.2​
2.85​
369.3​
3.04​
367.7​
3.02​
366.8​
3.00​
367.7​
3.02​
43gr​
365.2​
2.97​
371.8​
3.08​
369.5​
3.04​
366.0​
2.94​
371.8​
3.08​
372.7​
3.10​
370.2​
3.05​
0.40gr​
372.7​
3.10​
371.0​
3.07​
368.5​
3.03​
372.7​
3.1​
371.0​
3.07​
373.5​
3.11​
367.7​
3.02​
0.20gr​
0.40gr​
540.0​
2.69​
535.9​
2.67​
541.2​
2.72​
539.4​
2.70​
534.2​
2.65​
530.7​
2.62​
537.7​
2.69​

*In the near future I will repeat the same test with an Action Army 6.01mm-430mm inner barrel.
 

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I’d like to add that I had a good bump myself. I was using a standard EdGi piston with long air brake head. Probably weighs around 45g. My rifle was shooting ~315 fps with .48s.

Then I dropped in my EdGi SAP at 70g, air brake a little shorter and then my rifle shot ~365fps with .48s. Other components are an Airsoft Philosopher hopup chamber, random clear/hard flathopped bucking, 60° stalker rhop patch in a 300mm stainless 6.01 open window EdGi barrel.

While joule creep is “heavier bbs more energy” I still like to view joule creep as the difference between .20g output and .40g-.48g outputs WITH the hop set for the heavy weight. You can achieve any output if you slap the right parts in. I think it’s impressive when you have 500fps with a .20 and as high as possible with .48s.
 

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I’d like to add that I had a good bump myself. I was using a standard EdGi piston with long air brake head. Probably weighs around 45g. My rifle was shooting ~315 fps with .48s.

Then I dropped in my EdGi SAP at 70g, air brake a little shorter and then my rifle shot ~365fps with .48s. Other components are an Airsoft Philosopher hopup chamber, random clear/hard flathopped bucking, 60° stalker rhop patch in a 300mm stainless 6.01 open window EdGi barrel.

While joule creep is “heavier bbs more energy” I still like to view joule creep as the difference between .20g output and .40g-.48g outputs WITH the hop set for the heavy weight. You can achieve any output if you slap the right parts in. I think it’s impressive when you have 500fps with a .20 and as high as possible with .48s.
I think joule creep is potentially dangerous when not used right and only purpose when used in that context is to cheat chrono testing.

Build for joules on highest BB weight not fps.

As a mostly self regulating sport this should be the community mindset.
 

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It might stem from the fact that I’ve seen some people get seriously hurt before.

But I’m rather against joule creep as well and was incredibility surprised the relatively high support of it here when I first joined.

It’s one things to understanding it and use it to chrono the ‘real’ joule rating for the bb one is using (if you plan to shoot .45, chrono with .45). But seeing people get nearly .5-1J increase by exploiting ref/field lack of knowledge is really scary to me.
 

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What worries me isn't the joule creep or any other technical trick in order to improve the shots.
What worries me is the intentional ruse, deception and wile to violate the rules of engagement, minimum engagement distance & field safety rules. Worries me the players that only want to win or to make "kills" or "hunt" high fps by any means. It worries me the players that take the safety rules lightly...
And I've seen these cast of mind, attitude, mindset many times & I'm trying to explain and change this way of thinking in order to decrease the possibility of injures.
A sniper opened fired from 5m-7m with his 500+fps/0.48gr bb even though he heard me & knew that i was very close.

Players must learn to control their selves and then must learn to follow all safety rules.
 

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Few days ago I did a bb energy/fps/piston weights testing.
Platform: TMVSR10 pro
FPS: 530-540fps 0.20gr bb
Inner Barrel: ML C.J 550mm-6.04mm
HopUp Unit: Maple Leaf
HopUp Bucking: ML Mr Hop 70
Spring: Laylax SP150
Piston: Laylax PSS10 High Pressure (40gr)
*Zeroed HopUp
*Chronograph: AC5000
*BBs: 0.48gr BLS

Ammo
Piston Weight (gr)
Velocity (ft/s)
Energy (joules)
0.48gr​
70gr​
357.2​
2.85​
356.5​
2.83​
368.5​
3.03​
365.2​
2.97​
328.6​
2.41​
55.5gr​
367.7​
3.02​
370.2​
3.05​
357.2​
2.85​
371.0​
3.07​
368.5​
3.03​
322.1​
2.31​
47.5gr​
357.2​
2.85​
369.3​
3.04​
367.7​
3.02​
366.8​
3.00​
367.7​
3.02​
43gr​
365.2​
2.97​
371.8​
3.08​
369.5​
3.04​
366.0​
2.94​
371.8​
3.08​
372.7​
3.10​
370.2​
3.05​
0.40gr​
372.7​
3.10​
371.0​
3.07​
368.5​
3.03​
372.7​
3.1​
371.0​
3.07​
373.5​
3.11​
367.7​
3.02​
0.20gr​
0.40gr​
540.0​
2.69​
535.9​
2.67​
541.2​
2.72​
539.4​
2.70​
534.2​
2.65​
530.7​
2.62​
537.7​
2.69​

*In the near future I will repeat the same test with an Action Army 6.01mm-430mm inner barrel.
Did you manage to complete the test with the 430mm barrel?

I'm assuming the reason you gained fps with lower piston weight (s) is due to having a barrel that is too low cylinder/barrel ratio for the BB your using. The lack of momentum on low piston weights is pushing the air put slower so your getting a more effective use of air for the barrel length.
 

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Did you manage to complete the test with the 430mm barrel?
Not yet, but I will. Just don't know when. Before that I will also test 0.40gr, 0.43gr bbs
1tonne suggested me to try a shorter barrel 6.01mm/430mm
 
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