The Windham .223 and .300 blk MCS was a bit pricey for me, but it performs well. Essentially it is made to quickly convert your AR-15 setup from a .223 to a .300blk with little to no hassle. It comes with 2 barrels and 2 bcgs each for the respective caliber. One thing about it is that it is almost instantly ready to be fired once you get it, minus the time it takes to get your optic sighted in. And it functions very much like any old AR platform, however with this you get the option to use two different calibers. That was essentially why I bought it in the first place, because I wanted to have the best of both worlds without buying two completely different guns. With this, I get operator tier performance for 2 calibers. Highly recommended.