This is a LE-901 (Civilian version of the select-fire CM-901) It utilizes a stoner-esque direct impingement gas system and, with the help of a conversion block, can be converted to fire everything from .308 to 5.56 including 7.62x39mm, 5.45x39mm and 6.8 SPC with the correct upper and barrel. 

This particular rifle is lightly used and comes with 2 metal SR-25 magazines. 20070097

The link below shows the versatility of this rifle, PLEASE NOTE THE RIFLE FOR SALE IS NOT THE RIFLE IN THE LINK BELOW

https://modernfirearms.net/en/civilian-rifles/u-s-a-civilian-rifles/colt-le-901-eng/