I know a guy who is selling parts from his socom 16. I have a SA M1A I'm hoping I could changed it to the "16".  Is the piston that is used on the socom 16 rifle the sameone on a M1A or is it diffrent?
thanks for any info.

The difference is the gas cylinders slightly modified with a larger gas hole to adjust to the 16 inch barrel and it uses a one piece gas lock and muzzle brake. Everything else is the same.
If he's selling the barrel, muzzle brake/gl and cylinder than it's simply having a smith put on the barrel to your receiver and headspace the/a bolt to it, use that gas cylinder with it and muzzle brake/gas lock combo and everything else is the same.

he's saying that the piston is interchangeable, thats ture, right?