.308 Polymer Lower Receivers? (TNarms)

[HiMom47]

Anyone use these? Do polymer 308 lowers last? I'm thinking about the Tennessee arms 2 pack- one ar15 lower, one 308 lower for $135. Do you think polymer with metal on the buffer tube and grip screw receiver is strong enough to handle the power of a 308?

One AR15-One AR308-Engraved(optional)-Shipped

I'm thinking of these more as a back up recievers. But with it i could start slowly collecting the dpms 308 (ar10) parts. I think the 5.56 polymer will work. Not sure about the 308 one. Do you think it's worth checking out?? Or just spend the $250+ on a real 308 reciever? If anyone has had any expericence with any 308 polymer recievers? There is very little about them on YouTube. A lot of youtube videos just show it at the range taking a few shots. Did they last way past those few filmed shots?? Will I ever know???

I would love to see someone do a 5000 rd torture test on 308 polymer lowers.

 

[Checkers]

If you want to buy me 5000 rounds of .308 I'll do it

But I hang out on reddit.com/r/guns a lot (And AR15, Firearms, etc) and TNArmsCo is a user there, and everyone who uses his stuff seems to love it. I'm planning on buying one this friday when I get paid, but I have no idea how soon I will finish the build.

Hit them up on Reddit if you want, user TNArmsCo, but I would definitely trust them.

Edit: Here is their .308 injection molding process, and TNArmsCo answering question

 

[dsdmmat]

For about the same money ( 35 more) you could get a GO Balistic 308 lower, I have built a couple on them and they are a great lower. I got in on the first run and the second run of these lowers. Keep your eye out for these and jump on one when they come back in stock. Go Ballistic Firearms

 

[Checkers]

For about the same money ( 35 more) you could get a GO Balistic 308 lower, I have built a couple on them and they are a great lower. I got in on the first run and the second run of these lowers. Keep your eye out for these and jump on one when they come back in stock. Go Ballistic Firearms

The $135 OP is talking abou tget's him an AR15 lower, and the AR308 lower, not just the latter

So I'm not saying Go Ballistic isn't good, but it's almost twice the price

 

[dsdmmat]

The $135 OP is talking abou tget's him an AR15 lower, and the AR308 lower, not just the latter

So I'm not saying Go Ballistic isn't good, but it's almost twice the price

Ahh I didn't pick that up on the first read. Realisticly picking up an Anderson for 50 bucks or so and a go ballistics 308 Lower will still only cost 85 bucks more so it is not really twice the price ( close but not quite) . He did mention spending 250 on a 308 lower and there are really good quality 308 lowers a lot less than that. Personally I would not own a polymer lower for either the 223 or 308. To each his own though.

 

[BDSKJCHRIS]

no experience with them (yet) but i have some on order. they seem to be good quality but it will be a while before i can post a review as i do not have an upper yet and money is very tight.

 

[BDSKJCHRIS]

to update this: out of the box the tnarms 308 receiver seems to be very well made, unfortunately i can't give any sort of review on it's performance as i do not have an upper for it yet.

the polymer AR-15 lower is also a very nice receiver. i assembled one for use with my SAM-R upper. i have no worries about it's durability but there are a couple of things worth noting: if you plan on using a rifle length buffer tube then you will need to same the back of the receiver about 1/16" in order for the rifle length tube to retain the buffer retainer pin. TNarmsco has apparently fixed this with the new/updated receiver design and anyone who has to return an old one for warranty purposes will be upgraded to the new style as well.

as far as fitment to the upper (bcm upper receiver) it is great. there are a few areas which are intentionally sized for a very tight fit. those areas are the curve at the buffer tube and the slots/holes for the upper and takedown pins. they design the lowers to have a much tighter fit so that they can either wear in, or be lightly sanded or filed by the user for a more "custom fit" to their upper. the takedown pins are pretty tight right now, but i'm sure they will be fine in a few months.

also worth noting: when pulled out, the take down pins have a fair pit of wobble to them. its not a big issue but it is something that doesn't occur on an aluminum receiver, again not a big deal as they are super tight and rigid when pushed in. the safety selector has a minor amount of play in it as well, at either position, (safe or fire), the selector can move a bit, it doesn't feel as positive and rigid as a safety in an aluminum receiver, again it is not a big issue as the gun will not fire in the safe position no matter where the selector is in the "wiggle range" and when set to fire, no amount of wiggle will prevent the gun from firing. i suspect that either a stronger safety detent spring or a larger diameter and longer safety detent would solve this issue, (i think the amount of play is due to the difference in the size of the detent pin and the hole it goes in.

even though i have seen no reason to worry about it, i used kns gen 2 anti rotation pins for the trigger and hammer. for 2 reasons, i am using a geissle ssa-e and want the best trigger possible and it is extra insurance for the pin holes.

another benefit of the .308 receivers is that they take almost every part of a milspec ar-15 parts kit, the only thing needed is extended takedown pins.

 

[pseudonymity]

With the AR design I don't think that the lower material matters much in terms of resisting recoil. The bolt locks into the barrel extension and the carrier recoils back into the buffer tube. About the only thing that sees much recoil force on an AR lower is the take down pins, and unless the lower is made out of styrofoam I don't see the recoil being an issue for the lower.

The issue with polymer lowers is how well they hold up to non-firing stress, in particular at the hand grip mount point and at the rear where the buffer tube threads into the lower. Many polymer lowers are considerably thicker than aluminum ones in the portion right below the buffer threads for that reason.

 

[Blimey]

With the AR design I don't think that the lower material matters much in terms of resisting recoil. The bolt locks into the barrel extension and the carrier recoils back into the buffer tube. About the only thing that sees much recoil force on an AR lower is the take down pins, and unless the lower is made out of styrofoam I don't see the recoil being an issue for the lower.

The issue with polymer lowers is how well they hold up to non-firing stress, in particular at the hand grip mount point and at the rear where the buffer tube threads into the lower. Many polymer lowers are considerably thicker than aluminum ones in the portion right below the buffer threads for that reason.

One thing to consider is in the case of a NY compliant with the thordsen stock the stock's force is going into the grip tab instead of in a straight line through the buffer tube.

James madison tactical has nice lowers but they are unfinished. However, the grip tab has a brass screw insert to add some connectivity when screwing in.

I can't speak to 308 polymer lowers but the thing about ar15 one is that the bulk of people who have tried them have found they do fine.

 

[GUNSICK]

One thing to consider is in the case of a NY compliant with the thordsen stock the stock's force is going into the grip tab instead of in a straight line through the buffer tube.

James madison tactical has nice lowers but they are unfinished. However, the grip tab has a brass screw insert to add some connectivity when screwing in.

I can't speak to 308 polymer lowers but the thing about ar15 one is that the bulk of people who have tried them have found they do fine.

That's not the thordnsen stock it's an Aries rifle.

 

[BDSKJCHRIS]

The issue with polymer lowers is how well they hold up to non-firing stress, in particular at the hand grip mount point and at the rear where the buffer tube threads into the lower. Many polymer lowers are considerably thicker than aluminum ones in the portion right below the buffer threads for that reason.

the tnarmsco lowers (the 308 and the ar-15 ones) all have a brass insert for both the pistol grip screw and the buffer tube. nothing threads directly into polymer. the inserts and secured into the lower during the mold process

 

[pseudonymity]

I was thinking less about the threads themselves and more about the point where the greatest amount of shear force would be if opposite forces are applied to the barrel and buffer tube/stock. The area right between the buffer tube threads and the rear takedown pin hole is a critical area. All the force applied to the tube/stock is transferred to the threaded area, all the force on the barrel is transferred to the lower at the takedown pins.

I suspect that it really depends on the strength and elastic properties of the polymer material - they are not all alike. Shear forces are likely with tension being a bit less likely I think. Torque forces seem like they would be rare and compression seems really unlikely.