450Bushmaster.net

A number of manufacturers have testimonials and videos showing their polymer lowers being run with BMs, Socoms etc.

Anyone have any first hand experience?

Have no personal experience with big bore's and poly lowers. I would recommend against it, though.

I do have experience with an NFA poly lower that I bought on sale to play with. It had a tight upper to lower fit that I tried remedying, worked ok. Had a snuggish fit, not tight. Ended up splitting the lower right at the seam (where the 2 molds met) in the front of the mag well. Didn't even put a round through the build. Plus, a lot of people end up snapping the receivers at the back corner when installing buffer tubes.

There are a couple poly lowers I would maybe try for an Ultralight .223 build. Honestly though, it will only save you a few ounces in the end. Comparing lightest poly lower's to lightest, non-magnesium lowers, you have the Tennessee Arms clear "ghost" lower at 3.6 ounces and V7 2055 at 6.4 ounces. So 2.8 ounces. Even though they are lighter and cheaper, I wouldn't say they are worth it, unless you are going all out, and can't strip anymore weight out of the build. Just for reference, the lightest .223 rifle builds I know of are something like 2.8lbs. They are also basically range toys the way they are built. Plus I don't think you would want to shoot 450B that weighs close to that, do you?

IMHO, the greater the recoil potential of a caliber, the heavier I like them to be. Weight is the number 1 way to reduce perceived recoil. My lower of choice is my rare, DPMS, matte (dull grey) stainless steel one. There is no caliber available in an AR 15 platform that will ever imperil it. It handled my 300 WSSM upper just fine when I had it. Then again, I'm weird.

Hoot

I own 2 of the New Frontier LW--4. One on my 450 Bushmaster the second on my 7.62x39. Owned both for over 5 years plus years . No problem. Light weight, no slope and the carbon fiber has a life time warranty. Good luck

Good to know, thanks.

I had ATI poly lower break at the receiver extension on a 6.8 SPC. ATI replaced it, but I just don't trust them now. It was only 2 ounces lighter than the aluminum lower, so not worth it to me.

if you can dial your gas back so that your buffer never bottoms out, i'd probably be ok with it.

i just wouldnt be able to trust having one overgassed like most of these uppers are with the bufer pounding in the rear of the receiver extension not applying serious stress long term at the rear of the lower where the receiver extension comes in.

the new WWST2020 mk3 lower might have some potential in changing how those stress points act, but time will have to prove that out

https://www.youtube.com/watch?v=G6Rd6BKaJDo

Good point- thinking mid or carbine length system?