FMK AR Extreme polymer lower failure.

[Lazytrbar]

So, this happened. After about 200 rounds on the second outing. Broke right in half under fire. I felt flex, so pulled it away and could see daylight between buffer area and upper. Flexed with my hands and snapped in two.

Didn't think to take pictures until I had stripped it for parts.

Lower photo is what it looked like whole! You can see stress crack!!

Anyone want to buy a like new pistol upper!!

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[Irving]

Thanks for posting. I always wondered about the durability of the plastic lowers.

[20X11]

I only use Plastic lowers for my 22lr ARs that will never hammer the back of the buffer tube. Most pistols are over-gassed and really hammer the buffer.

[whitewalrus]

Does the MFR offer a warranty? Even if not, may want to contact them over this.

[Lazytrbar]

Does the MFR offer a warranty? Even if not, may want to contact them over this.

Past warranty period. "Not meant for pistol builds".

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[Zundfolge]

Further evidence that plastic versions of metal lower designs are probably not wise.

The WWSD 2020 lowers should be available by the end of the summer (although you'd have to use a different upper or register it as an SBR with that upper).
https://www.brownells.com/guntech/ww....htm?lid=17958

Maybe a dab of Gorilla Glue would take care of it

[XJ]

I still take a CavArms mk2 out every now and then, it is 17ish years old still going strong

[Sawin]

Definitely not for pistol builds, unless the gas block has been adjust way down. Even a heavy buffer is gonna put a lot of inertia into the lower receiver extension (buffer tube).

[Grant H.]

Polymer lowers suck. Always have, likely always will.

I've seen everything from Bushmaster Carbon Fiber to cheap Poly80 lowers fail.

It'll be interesting to see what comes of the WWSD stuff, but I don't have high hopes.