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JJ_BPK
05-07-2015, 06:26
I have seen these plastic lower AR receivers around for a while.
I have told those that asked, that I do not support plastic for any cal other than 22lr.

BUT the price is outrageous..

http://www.tnarmsco.com/ar-style-hybrid-lower-any-color/

Now a 7.62x51 (308) model??

http://www.tnarmsco.com/ar-308-presale-available-mid-2015/

Anyone with experience using these or similar plastic lowers??

x SF med
05-07-2015, 18:00
I saw some, was not impressed, haven't fired using one.

MR2
05-07-2015, 18:26
Reinforced Nylon 6-6 with Marine Grade Brass threaded inserts molded into the buffer collar and pistol grip for strength and corrosion resistance.

These are not plastic. Plastic ones I've seen can crack where the hammer hits the frame by the magazine well and up where the buffer screws into the frame. This is usually along a mold seam. Have heard of cracks along the length of the upper receiver.

Have not seen a nylon lower, so... I like the idea for an AR pistol. Maybe some 3-gun rigs.

PhyrricVictory
05-08-2015, 13:34
I've tinkered around with the model of one and a 3D printed ABS version. Never assembled or tested though due to the ::cough:: wonderful ::cough:: state that I live in and safety concerns.

I've had some ideas of making a light-weight lower through using 3D direct metal laser sintering and having the internal structure of the /lower be constructed like you see on those 3D printed arm casts with an outer shell to prevent it becoming filled with debris. I'm a long ways off a prototype though as I'm still working on figuring out a lot of the stresses that the receiver sees and estimating external forces on it and running the required analysis in ANSYS. (It makes no sense to make it lighter if it fails when you need it) Conservatively will be a 20-35% weight savings (off a T-6061 aluminum solid billet milled receiver) if I can get the numbers to work.

Box
05-08-2015, 13:42
so...
wouldn't these lowers be as durable as any of the other "plastic" guns on the market?

I wonder what kind of compound they used to mold these things. It seems like a decent upper put on top of one of these buggers would make for a pretty decent plinker
Maybe not a match grade gun but it does cost match grade either?

it does look worth a try though

x SF med
05-08-2015, 17:03
so...
wouldn't these lowers be as durable as any of the other "plastic" guns on the market?

I wonder what kind of compound they used to mold these things. It seems like a decent upper put on top of one of these buggers would make for a pretty decent plinker
Maybe not a match grade gun but it does cost match grade either?

it does look worth a try though

The ones I saw, at a GBF function, did not seem to be made to the tolerances or quality of a machined lower the edges were sharp where they should have been smooth, rounded where you would expect clean sharp edges, and some areas had molding 'run out' in areas where it would be difficult to clean up, but could interfere with internal mechanisms.

JJ_BPK
05-08-2015, 17:08
so...
wouldn't these lowers be as durable as any of the other "plastic" guns on the market?

I wonder what kind of compound they used to mold these things. It seems like a decent upper put on top of one of these buggers would make for a pretty decent plinker
Maybe not a match grade gun but it does cost match grade either?

it does look worth a try though

My 1st worry would be stress cracks in the cross pin areas.

After that I would worry about the trigger, hammer, sear pin and wobble.

Then the castle nut threading on to the receiver and torque on the butt stock cracking in that area.

Then galling in the mag well.

Not much, but worrisome..