Polymer vs. 7075-T6 Alloy stripped lowers
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Old 05-06-2014, 12:47 AM   #1
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Default Polymer vs. 7075-T6 Alloy stripped lowers

Well, I'm squarely in the "buy a milspec 7075-T6 alloy lower" camp though I know many people like to try out polymer lowers. But I just don't see the advantage of polymer. Weight or price (since if you catch a sale there are $50-75 milspec stripped lowers.) Also no one has been able to prove their polymer lower is stronger than 7075-T6 alloy.

Comments are welcome...

Of course many vendors and polymer fans claim the polymer lower will save you a pound of weight or 1/2 pound but when you compare the weight of stripped lowers there isn't much difference. (Larger differences tend to be complete lowers somehow fudged toward a big polymer weight savings. Heavier stock, heavier buffer, BAD lever, etc. added to the alloy lower.)

Approximate stripped lower weights:

8.5 oz ... Milspec 7075-T6 alloy
8.0 oz ... ATI Omni hybrid (fiberglass with zinc inserts)
6.8 oz ... Amalgamated Ti titanium
5.9 oz ... Mag Tactical (proprietary alloy)
5.5 oz ... Generic magnesium alloy
4.5 oz ... Bushmaster Carbon-15
4.5 oz ... New Frontier LW-15

For a 4 ounce or less savings toward the rear of the rifle where there's little impact I just can't see taking a chance on polymer, maybe there are good ones but for hard use I don't trust their durability.

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Old 05-06-2014, 12:54 AM   #2
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call me old-fashioned or whatever, but it took me long enough to come to terms with polymer pistols!

while polymer lowers may work and work just fine, i just can't seem to get to the point i would have confidence in them for the long term usage as being able to handle the abuse an alloy lower could.

that is strictly a personal opinion and nothing more. i have no proof or evidence to support my opinions on this.

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Old 05-06-2014, 07:09 AM   #3
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Even IF i'm 70-80 years old.. holding or carrying an extra 4oz, i won't notice the differences.
My local LGS, New Frontier Armory manufactured those polymers and i never heard anything bad about them. Good company to deal with, best prices and best customer service in town. But still, polymer lower isn't my cup of tea.

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Old 05-06-2014, 07:25 AM   #4
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I like my alloy lower, only because I previously owned a new frontier lower and it kind of had a cheap feel in my opinion. I'd say its lighter weight, really just a personal choice

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Old 05-06-2014, 07:45 AM   #5
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Well, I like light weight and 4 ounces, though it doesn't seem like much, is the weight of an Aimpoint Micro with mount.

If it were possible to make the polymer lower as durable as forged aluminum, I'd be all over it. In real world, non-SHTF fantasy usage, so long as you don't abuse it or assemble it incorrectly (and those are big if's), a polymer lower should work just fine.

If you put steel inserts into the pin holes and some sort of steel insert into the back of the stock where the buffer tube assembly lives, then you might have something. I'm guessing that something that's properly built of polymer (with reinforcing steel inserts) will weigh nearly as much as the forged aluminum lower. The polymer Bulgarian AK "waffle" magazines are a good example of this. They're just as durable as the steel magazines, but they also weigh nearly as much.

The only significant weight savings to be had in the AR platform is the barrel and bolt carrier. By shaving weight off of a variety of parts, if you do it with enough parts, you could lose an extra pound or so off the weight of a stock lightweight AR-15 but that's about it.

If they can nickel boron line cobalt alloy barrels, then perhaps you could lose another pound of weight. After that, you're reaching the design and materials science limit with respect to weight.

A 4 pound carbine is entirely possible, but you're going to give up some things for that.

If you put the recoil spring behind the charging handle or in front of it, eliminate the buffer assembly, use a carbon fiber upper receiver and polymer lower, use a folding aluminum front sight (or no front sight), lose about half the mass of the bolt carrier, and replace the steel barrel with a cobalt alloy, then you could make a sub 4 pound carbine. This carbine would cost about 2K-2.5K, about half of which would be the expense of making the barrel, but you could, theoretically, have a full up weight (with optic, white light, and loaded 30 round PMAG) of 5 pounds.

That'd be pushing engineering and materials to the current limit.

I'm currently waiting for the ICE-15, but Rick Crommett hasn't found a manufacturer yet. If/when he does, I will be one of his first customers.

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Old 05-06-2014, 11:49 AM   #6
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You don't get to a 4 lb gun safely by making 1 lb weight reductions. You get to 4 lb by losing a few grams here, an ounce there. Really, I don't see the point of a 4 lb combat rifle. At some point you are going to have men in hand to hand combat. A 4 lb plastic rifle only gives the soldier one option, attempt to run the enemy through with the barrel. I hope no one has to block a wild swing of a knife with a 4 lb rifle.

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Old 05-06-2014, 11:52 AM   #7
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The biggest advantage if a polymer lower is manufacturing cost. The folks who benefit most are the manufacturers. The material costs less, the machining cost and anodizing cost is reduced or done away with in some stages. Then the final product is sold for a little less than or sometimes as much as an aluminum receiver.

Variety is probably the only advantage for the consumer. The confusion and competition may help keep the prices of aluminum lowers competitive when the market isn't nuts.

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Old 05-06-2014, 03:27 PM   #8
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Milspec aluminum all the way, and billet if I get that choice!

That said I do have a polymer lower on a purpose built 22lr AR. Its solid and works well, just not a combat rifle....

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Old 05-06-2014, 03:35 PM   #9
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Milspec aluminum all the way, and billet if I get that choice!

That said I do have a polymer lower on a purpose built 22lr AR. Its solid and works well, just not a combat rifle....

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Old 05-06-2014, 06:31 PM   #10
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Quote:
Originally Posted by SSGN_Doc View Post
The biggest advantage if a polymer lower is manufacturing cost. The folks who benefit most are the manufacturers. The material costs less, the machining cost and anodizing cost is reduced or done away with in some stages. Then the final product is sold for a little less than or sometimes as much as an aluminum receiver...
I agree. And an ideal way to find out firsthand would be finishing an 80% lower, which would be a heck of a lot easier if it's polymer. Just imagine the difference in effort roughing out an unbroached magwell - alloy vs. polymer! It is amazing that a finished alloy lower can be sold for $50 but not something manufacturers enjoy doing. They surely would rather make a greater profit selling polymer receivers.

We know polymer works in some firearms that were designed for it but when it comes to the AR, I'll use receivers made of the materials it was designed for.
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