Tonight's AR15 project

[righter13]

Probably. But the receiver extension junction has been a known weak spot for a long time.

Like ASH556, I have my doubts about the story given by the owner of the rifle in the OP. It's unlikely that it broke after one round. There was probably some preexisting damage that went unnoticed until it was fired.

Can't speak for the OP but the one I posted pics of was a EP80 80% poly lower that shattered after one shot of green tip.

 

[lostgeorge75]

Like ASH556, I have my doubts about the story given by the owner of the rifle in the OP. It's unlikely that it broke after one round. There was probably some preexisting damage that went unnoticed until it was fired.

I wouldn't doubt micro cracks or some invisible stress damage happens when trying to torque down the barrel extension nut on those poly lowers especially without the right tools and vise blocks.

 

[mtdawg169]

Can't speak for the OP but the one I posted pics of was a EP80 80% poly lower that shattered after one shot of green tip.

Wow. That is awful.

 

[righter13]

Wow. That is awful.

I blame myself... Never should have used Green tip. To dang powerful.

 

[ASH556]

I blame myself... Never should have used Green tip. To dang powerful.

ROFL! Forget about armor penetrating, that stuff's lower receiver penetrating!

 

[Falcon1]

I blame myself... Never should have used Green tip. To dang powerful.

My thoughts exactly.....That stuff is dangerous you know.

 

[19 Kilo]

I've been hunting with a 6.8 and 300BO with an Omni lower for a few years now with no problems, but that's just hunting. I might shoot 20 rnds a year with these two lowers at best, light weight was what I was going for and got it. Given the choice, I would go with the light weight metal lowers now offered for the same rifles. I plan to go that route with the hunting pistol I'm building for this year because of climbing stands being used more.

I have seem Anderson lowers missing holes before, had one without the front pin hole drilled.

I did have to work on the upper/lower pin alignment with both Omni lowers, but it's polymer so no big deal. I built both rifles out of spare parts that I had so I've got next to nothing in them. The 6.8 looks stupid with a carbine rail on a mid length gas system on it, but the deer and hog don't seem to complain.

 

[Wallace's]

I think that's just the weakest point, and you have a hole there. I think Tennessee arms bulks up that part of the lower. Like someone said earlier, you can make a poly lower, just not one that a carbon copy of aluminum ones.

Doubt the temperature had anything to do with someone stepping in it. That plastic probably just has a low tensile strength compared to aluminum. As noted before, that shape was engineered for forged aluminum, not glass fill N6, N66 or whatever polymer type they used.

 

[Wallace's]

Another thing, not sure if certain cleaners or solvents act like a plasticizer weakening the lower. We run a spin finish additive at work (very similar to hand soap) that will break down many plastics until so brittle they break apart in your hand.