Thanks for the help turned out to be the piston in the end, threw the old one back in and works perfect now, so i think the plastic on the piston that came with it is rubbing on it that or its getting caught on the sear, i'll investigate further when i have more time.
The product was;
https://www.zerooneairsoft.com/product_info.php?products_id=11541
just the standard upgrade kit complete with steel cylinder, shorter spring guide, some spring most prob the ares 500 fps one and the piston you can buy from pretty much anywhere.
https://www.skirmshop.co.uk/ares-cpsb-45-piston-for-striker-as01.html piston.