Thumbhole stocks as a method of reinforcing magnesium or polymer lowers...

[TED]

It seems that magnesium or polymer lowers, when they fail, fail at receiver extension or buffer tube extension area.

I think that maybe using a thumbhole stock may help reinforce this area and reduce the occurrence of such failures.

The downside is that you would likely then lose some of the weight reduction.

TED

[everready73]

I just don't use poly lowers

[HeruMew]

If you want polymer lowers, buy CAV Arms Poly. Way way worth their cost. The TN Arms Poly suck majorly. I will be slapping a cheap upper on mine if I don't sell it or trade it first.

[TomMcC]

If you want polymer lowers, buy CAV Arms Poly. Way way worth their cost. The TN Arms Poly suck majorly. I will be slapping a cheap upper on mine if I don't sell it or trade it first.

I thought the TN Arms lower was supposed to cure the poly deficiencies. Didn't work?

[HeruMew]

I thought the TN Arms lower was supposed to cure the poly deficiencies. Didn't work?

Material is fantastic.

Their customer service is crappier than a pig pen. The product itself has ALOT to improve on.

Dimensions are out of spec for the detents, they stretch and get stuck. Safety swings dang near 25 degrees freely when on the detent.

It works, it worked well in fact (in regards to firing, holding the FCG, and actual function). I loved the brass inserts, but the issues with material stretching/breaking at the detents ruins it all for me.

I paid shipping for them to replace the first one, I get the second one back and it's out of spec as well.

I ask them how they wanma handle it, I was pretty much ignored and advised the product is doing as designed.

I don't trust a free swinging safety lever, nor do I want to hammer my takedown pins in and out until the polymer breaks and it no longer detents anyways.

It's a cheap product that simply isn't worth it. Go Anderson (if trying to be cheap) and at least have some solid safety movement and easy takedown pins. Though I won't buy Anderson anymore due to issues with a big percentage of the ones I have had hands on. But when they're in spec, they work wonderfully.

ETA: Oh, and the BHO would get caught behind the followers on a few types of magazines due to it needing more material in front of the BHO slot due to material stength. GI mags worked well. But some of them would have the bolt hitting the follower instead of the BHO. Their cure was modifying a 9MM colt catch and taking off some of the follower bar to accomodate the extra distance.

Eff all that noise. Spend almost the cost of the receiver to mod a part so it will work properly? Nah.

[TomMcC]

Got it, sounds like the plastic is just too rubbery.

[GH41]

A serviceable receiver could made from a magnesium billet and FRP but not at a price point most of us would be willing to pay. Nothing wrong with either material. Check out what they build airplanes out of these days. Plenty of thumbhole AR stocks out there if you want to try one. Google AR15 Thumbhole stock pictures. There is a really cool carbon fiber stock that probably cost more the the average rifle.

[georgeib]

Pretty darn sure that the best way of reinforcing poly lowers is to make them out of forged 7075-T6 aluminium. And not by adding a bunch of bandaids.

My mind is genuinely blown at how they are even a "thing," I mean WTH??? The CAV Arms being the only possible exception.

[Jonnyt16]

Pretty darn sure that the best way of reinforcing poly lowers is to make them out of forged 7075-T6 aluminium. And not by adding a bunch of bandaids.

My mind is genuinely blown at how they are even a "thing," I mean WTH??? The CAV Arms being the only possible exception.
Those were my thoughts as well. Not to mention polymer AR-15 lowers just seem....sacrilegious to me.

[wanderson]

I’ve had a Plum Crazy & a New Frontier poly lower. At the time they were $100 each for a complete lower compared to $250-300 for a complete RRA or Stag lower.

Except for springs, mag & bolt catch all small parts were plastic too. That’s one problem. After a few years of use the NFA fcg hammer started to fail and doubletap. I replaced it with a steel single stage, but a few years after that the retainer pin for the takedown pin sheared off. I replaced all parts for both takedown pins. But when some of the threads for the grip screw came out while swapping grips, I was done, and rebuilt both with Anderson & PSA lowers and mil spec parts.

As for weight reduction, I don’t think it’s worth it. The Cav Arms lower is supposed to be a few ounces lighter than a Bushmaster carbon 15 lower but you have no grip or stock options. Personally, I think there’s more benefit in keeping the upper light, if we’re going by feel and balance. That’s why I run a 14.5” pinned mid length upper with a pencil profile barrel.

I also have a magnesium lower on another range toy build, It was $30 and unfinished and I liked the look of it. So far no complaints. Don’t care that it’s lighter, it was cheap and available, and is on a 5.45x39 built and only shoots corrosive ammo. The magnesium lower is reinforced where the FCG pins go, and uses it’s own pins. So not sure if that would be a problem for some triggers.

[The_War_Wagon]

NO.

Sarah Brady butthole stocks were conceived in hell, and there they deserve to die. Mating one bad idea, to ANOTHER bad idea (poly lower), does NOT make a good idea. :bad:

[SomeOtherGuy]

Got it, sounds like the plastic is just too rubbery.

The CAV-15, now made and sold by GWACS (http://www.gwacsarmory.com/lower-receivers-ar-15/), works just fine. The design is modified for the properties of polymer rather than aluminum. Wall thicknesses are greater in many areas, and the grip and stock are integral, avoiding what would otherwise be weak points.

There are very few occasions where you can make a huge material change in a properly engineered whatever and have an acceptable result. With the AR-15, you can use steel instead of Al at the same dimensions and everything will work fine, you just have triple the weight. Switching to anything lighter/weaker/more flexible without extensive engineering is asking for trouble.

[Dionysusigma]

Weapon weight is in the barrel, optics, and ammo. You're not going to make a car handle better by filling the tires with helium instead of shop air.

[Dionysusigma]

Further numbers to support this: Per their website, a Colt 6920 weighs 6.95 pounds (111.2 oz). A mil-spec stripped lower weighs 8.5 oz. This means that the forged lower makes up 7.6% of the rifle's total weight.

Sources:
https://www.colt.com/detail-page/colt-le6920-carbine-223556-161-301-pmag-mbus-4-pos-stk-blk
https://docs.google.com/spreadsheets/d/1I6Qb6kAJjChEJ56qhznv2291c5UHRDyNXuSXGObumqM/edit#gid=558510150