Originally Posted by Cc426

The barrel profile is different as well. The flash suppressor model comes with a pencil barrel which helps keep the weight down. The compliant model comes with a heavy profile barrel which soaks up heat better for more accuracy over an extended firing period.

There are actually 3 models that are similar (excludig cammo models) The first picture looks like the ca compliant model and the 2 picture looks like a compliant model.

So to break down all the differences:

Normal model - 20 round pmag, ambi mag release, 6 position stock, flash suppressor, pencil barrel

CA compliant - same as normal model EXCEPT: single side mag release, 10 round magazine, bullet button for mag release

Compliant model - heavy profile barrel, no flash suppressor, fixed/pinned stock, 10 round mag, bullet button, single side mag release

To add a flash suppressor properly, you have to remove the barrel, get a machinist to thread it, and then add flash suppressor. There are some clamp on type flash supressors but I wouldn't recommend them.