Polymer lowers are safe and will work just fine. The way the AR platform works puts all the stress and pressure on the upper (though that's not much anyways because of the way the direct impingement system works with the locking lug and carrier system) and the only real stress applied to the lower is the load applied to the hammer pin and the load placed on the buffer tube and carrier. If you don't drive over your rifle with a truck or do terrible things to it, you will have a rifle that will last a lifetime. That being said, brads has stripped lowers for $50 in the classifieds and there are a few shops with similar deals on forged lowers, so there isn't a real reason to buy something that is weaker than the standard lower.

If you are wanting to go the 80% route (which is ALOT more involved than most people think), tactical machining has raw 80% lowers for $29 and black anodized ones for $43.

Thanks for the info! I am just going to go with forged stripped lower. Now the fun of picking out the pieces begins!!

Skip to 7:20 where he runs the lower over repeatedly with his truck. Good to go.

That's pretty impressive. I was more referring to the fact that if you don't abuse a polymer/cheap lower in general, it will last a lifetime. I know a few shops have made polymer lowers in to machine guns and they get hammered and abused but they aren't as strong as a metal one (more from an engineering/numbers standpoint). You can't really go wrong either way.

I'm impressed with TN Arms Co. I stocked up on 3 of their new Gen 5 lowers after shooting over 3k rounds through one of their Gen 4 lowers. I've been very happy with them, and I think their lowers fall into a whole new category of polymer lowers. My next AR build will be a TN Arms FDE lower with a 16" 7.62x39 upper slapped on it.

As one of the other posters stated there isn't much stress placed on the lower receiver at all. I think if you want to try an 80% polymer lower then go right ahead...it'd a fun little project.

I have polymer 80% lowers in every form imaginable: nylon, carbon fiber reinforced, kevlar reinforced, long and short strand reinforcement, the possibilities are endless.

If you decide you want to try one I have plenty of extras. The Polymer 80 brand ever come with all of the bits you need for completion. Just pm me if you have any questions. I hope this helps...