Will this build kit work on an AR-9 lower receiver or only works with the AR-15 as it says above? — 2 Answers

You can use these uppers on a standard AR lower with the use of mag adapters or Endomags. You're probably going to have the best results with a dedicated Glock lower. FM makes one of the best Glock-fed lowers on the market. Their LRBHO mechanism is brilliantly engineered. Many manufacturers struggle to get this right, some ignore it altogether. FM's design has functioned so well for so long that some manufacturers choose to have FM build their lowers. I've had a FM-9 built around a CMMG radial delayed blowback bolt & barrel set I purchased here at Optics Planet years ago. Almost 4 years later I'm still impressed everytime I take it to the range. FM may be more budget range when it comes to price but you would never know it by the fit, finish & function. The finish machining is flawlessly and the anodizing & nitride coatings on the parts are deep, rich, dark and look exactly the same as you'd find on much more expensive options.