Polymer vs. 7075-T6 Alloy stripped lowers

Discussion in 'AR-15 Discussion' started by Quentin, May 5, 2014.

  1. Quentin

    Quentin New Member

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    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.
     
    Last edited: May 5, 2014
  2. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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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.
     

  3. okdonk

    okdonk New Member

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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.
     
  4. Mde

    Mde New Member

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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
     
  5. kbd512

    kbd512 Well-Known Member Lifetime Supporter

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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.
     
  6. John_Deer

    John_Deer New Member

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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.
     
  7. SSGN_Doc

    SSGN_Doc Well-Known Member

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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.
     
  8. dwmiller

    dwmiller Well-Known Member

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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.... ;)
     
  9. dwmiller

    dwmiller Well-Known Member

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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.... ;)
     
  10. Quentin

    Quentin New Member

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    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.
     
  11. Ez2b

    Ez2b New Member

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    I might be wrong but I think all polymer lowers have just been made illegal in the manufacturing they were made as a weapon and then filled with a different color polymer which in fact made it not a 80 percent lower
     
  12. kbd512

    kbd512 Well-Known Member Lifetime Supporter

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    Here's why you might want a four pound carbine. Let's say you have to carry other stuff with you (I know, civilians generally don't have to, but the military makes you carry things). If you're infantry and you're in an urban area, let's say you have either a shotgun (breacher), .30 caliber rifle (DMR), radio (radioman, obviously), or observation equipment (command).

    With a 4-5 pounds of weight savings over current issue M4 carbines (working configuration, not the weight of the carbine itself) you can carry a lightweight bolt-action .308 rifle/carbine (there are a variety of hunting rifles in the 5 pound category), that's most of the weight of a breaching 590, although a loaded 590 is heaver than that. These days 5 pounds is a radio with battery and accessories or observation device (stabilized binoculars, telescope, or ruggedized tablet for maps).

    With current technology we can already produce a 4 pound carbine (aluminum upper, polymer lower, HK style retracting buttstock, lightweight optic/white light/laser, chopped bolt carrier).

    When you find yourself in hand-to-hand combat, you're not going to want to use your carbine against them. That's what knives, clubs, and tomahawks are for.

    A good folder and a small, lightweight hawk are all that you need.

    If you have a folder and a hawk, it's going to be difficult for someone to use an empty AK-47/AK-74, with or without a bayonet, against you. Also, you don't block slashes, you get out of the way or get inside the swing. This works better when you don't have to hold onto a 8-9 pound pendulum with both hands.

    With a 4 pound carbine, if you're empty or it quits working, you can let it hang because it doesn't have sufficient weight to injure you. From experience, dropping a 8-9 pound carbine on its sling can be hazardous to your boys.
     
  13. kbd512

    kbd512 Well-Known Member Lifetime Supporter

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    BATFE incorrectly assumed that the polymer lowers were made as functional AR lower receivers first and then filled with a polymer plug. The manufacturing process was actually the reverse, however. The body of the receiver was formed around the plug and so, it is not a firearms receiver that has been subsequently rendered inoperable. The 80% lower was never operable to begin with.

    That said, BATFE doesn't like it when people find ways around the asinine rules designed to prevent the law abiding citizen from arming himself in an inexpensive and practical way, thus they are making up a story and sticking with it. Basically, they're making a false accusation (knowingly filing false official police reports), stealing lawful property from its lawful owners (each theft is a felony), and proclaiming that which they know to be untrue based on the rules/guidelines the FTB has set for to be a violation of the law so they can confiscate property (knowingly making false official statements).

    I'm not sure how many felonies they've committed in this incident alone, but the grand total just for this incident has to be staggering.
     
  14. sweeper22

    sweeper22 New Member

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    Polymer lowers are good because...

    I'm pretty sure they'll stand up to most abuse. The truth is, lowers really aren't subjected to a ton of wear and tear. If your gun is set up as you'd like it (and has a polymer lower), I can find no reason to tell you your lower is inferior. And poly lowers are both light and resistant to basic wear (abrasions and such). Lighter weight is a nice feature.

    Poly lowers suck because...

    They're generally not made by highly reputable companies. They'll minimize your rifle's resale value. And (when building) poly lowers can fracture when hammering in a critical piece...and I know this from experience.

    I think poly lowers absolutely can and do work. But every one of my personal ARs is built on an alloy lower. And I don't have much interest in building on polymer lowers in the near future. Considering I can get a really good alloy lower for just north of $50, it just doesn't add up. Maybe someday that'll change. Things often change.
     
  15. fsted2a

    fsted2a Active Member

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    I have a poly lower; I was thinking of building a .22LR around it someday. Everyone I talk to says that would be what they would do. Can't see using it for a 5.56 build. I know people with older Carbon 15's that haven't had a hiccup with their AR, I just prefer not to use polymer receivers in my 5.56 builds at this time.
     
  16. KG7IL

    KG7IL Active Member

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    the only money I'll spend on a poly lower is the $25 I just donated to the EPArmory defense fund.

    Maybe I'll get one in he future for a lightweight .22 lr conversion build.
     
  17. fsted2a

    fsted2a Active Member

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    I think a lot of us are thinking along those lines.
     
  18. dwmiller

    dwmiller Well-Known Member

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    I
    Works good for that roll. My purpose built lightweight is 4.25 lbs and has held up for 5000+ RDS. Carbon fiber tensioned tube barrel helps a lot with weight, and makes it a tac driver. Don't go overboard on hand guards, they add weight fast. Mine wears a carbine length CF free float tube. One 2" length of rail added in case I want to add the bipod for the bench. Internals are the cmmg stainless kit.

    One word, spring for the special charging handle. I stuck a 22lr in my original milspec handle. Pain in the a%%! The black dog mags are great. Solid and dependable feeding. :beer:

    Great cheap shooting trainer with correct AR controls! Not as accurate as my 10/22 bench gun but plenty good enough to squirrel hunt with to 75 yards, and a lot easier to carry!... :D
     
    Last edited: May 11, 2014
  19. fsted2a

    fsted2a Active Member

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    Question: what brand/model charging handle do you recommend for such a build?
     
  20. dwmiller

    dwmiller Well-Known Member

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    Last edited: May 11, 2014