? about regulator piston

[EnW]

What is the difference with the reg. pistons?
I have heard that you need to upgrade the piston when going to high pressure air. How do you know which is which?
What year did they change them?
Are there any drawbacks if I'm using the wrong one?
THANKS!!!!

[Army]

The odds are extremely good that you already have a high pressure piston. Switching from Co2 to nitro will require no change.