Gothic.308

Hi, I've been into airguns for years, and want to try airsoft, realism and recoil is very important to me, as I want to do some milsim. I don't know where to start, my local shop only had AEG's, I liked their TM M4 AEG, but I would prefer gas. I'm open minded to the platform, want either a rifle or SMG. Budget is about £600, any recommendations or advice would be great!? Thank you. :)