I'm definitely committed to getting a few of these New Frontier Armory composite lower receivers. I'm simply not buying the hype from some people that they're junk, because I have doubts they either own one, or they're comparing it to something of much higher quality. Meanwhile, there are those who are giving them rave reviews. http://www.joeboboutfitters.com/New_Frontier_Armory_STRIPPED_AR15_Polymer_Lower_p/nfa-stripped.htm These are not the same as PlumCrazy cheapo plastic receivers, and apparently are stronger than the Bushmaster Carbon receivers. Some people have complained about tightness of fit of some components. Others have noted the possibility of cracking. The cracking is what I'm worried about. Nobody has experienced this (with THIS brand) that I can find. One person even froze his, tied it to a string and slapped it against the concrete repeatedly with no ill effects. So I was wondering - technically - WHAT exactly would cause the cracking? Most of the brunt would be taken by the upper half where the bolt carrier is riding, right? And the springs would be absorbing much of the recoil energy, right? Please inform me.