I believe there is a little bit of give if the rail is over toqrued. Over the weekend I threw on a Moe foregrip on someone's AR and noticed that if it the additional rail was tightened too much, it was next to impossible to slide the AFG on. Loosend it up a tad and it slid on with less work. Still I would certainly trust Magpul's product.it just seems like there would be a lot of flex in a polymer rail section on the bottom of the hand guard. I'm probably wrong. I've never been let down by magpul before!
DS