Yes this is semi automatic but this is 6.5 Grendel not 223/5.56. don't believe they make 50 round 6.5 Grendel magazines. Hope this helps.

Yes, semi auto, and it could take a 50rd magazine if there were such a thing. Looks like 6.5 Grendel mags top out at around 25. buymymags.com/asc-6-5-grendel-ar-15-25-round-stainless-steel-magazine/

Found a 26 here
budsgunshop.com/product_info.php/products_id/45222/cpd+magazine+ar15+65+grendel />-----------
Another here
budsgunshop.com/product_info.php/products_id/48193/alexander+arms+26+round+blue+65+grendel+magazine />-------------

This is full semi-auto bro and the largest magazine-clips i could find in stock are 24rd. In stock here
budsgunshop.com/product_info.php/products_id/713088534/e-lander+magazine+65+grendel

Brad, it is Semi-Auto and 25rd is about it for Magazines : ammosc.com/6-5-grendel/