Piston weight and it's effect

[sonofsammo]

I've just got hold of an SRS sport, which is a lovely piece of kit.
I was planning on running it stock, and just changing the spring to m150, which I did.
But I got 2.88J on .4's - so I cut the spring down, just so I could take it out last weekend.
In the meantime, I ordered the variable mass piston, airbrake piston head, a new m150 spring and a supressor.

Because I'm new to all this, I'm at a bit of a loss as to where to start with the variable mass piston.
I'm aiming for a build running as close to 2.3J as possible.
So - where's a good guess to start with the piston? Should I go heavier or lighter?

Cos basically, I have no clue what I'm doing at all... ?

 

[sevizy]

As far as I know, up to a certain limit where the weight is too much a heavier piston will increase the Joules on heavier ammo (Joule creep) so the heavy piston should have more joules than a lighter one running at the same FPS when running heavy ammo.

 

[Davegolf]

I don't see the point of any piston weight increase on a spring powered gun.

The power producer / energy source is the spring, period.

A heavier piston takes longer to accelerate and ultimately transfers more energy into the cylinder head when it stops, assuming you are marginally over volumed.

This is also noisier.

A lighter piston will enable the spring to transfer its energy faster, whilst also reducing the shock load transmitted to the cylinder head every shot.

Energy (joule creep) gain is all down to cylinder volume vs barrel volume vs spring power.

Air brakes are cool but I would optimise your volume ratio before playing with the air brake.

If you have more volume than you need left over once optimised then take up the remaining cylinder space with air brake.

If no volume left over then you can't air brake without hurting performance!