Another AR lower poll

Discussion in 'Firearms' started by JABECmfg, Sep 27, 2013.

  1. Yes, 7075 is the best!

  2. Maybe, but not enough that I'd pay more for one.

  3. No, they're both Aluminum.

    0 vote(s)
  4. The real question is, billet or forged?

  5. I don't know, but I'd like to learn more about it.

  6. I don't care - I want something pink, to match my Hello Kitty furniture.

  7. Irrelevant - I am loyal to a particular brand.

    0 vote(s)
  8. These days, I'll buy anything that's in stock.

Multiple votes are allowed.
  1. JABECmfg

    JABECmfg multi-useless

    Lots of threads on AR's lately, which reminded me to post this poll.

    With a nod to @DarkLight who first brought up the point, I ask the monkey tree - is an AR lower made of 7075 Aluminum superior to one made from 6061? Assume T6 temper, same manufacturing methods, and everything else held constant.

    This is part of an ongoing search for opinions on AR lowers, and the first poll (billet vs forged lowers) can be found here: AR lower receivers - a question | Survival Monkey Forums

    Results of this poll may also influence the direction of another AR thread (not specific to receivers) that I started earlier today, in which we ask by what standards should we judge an AR and why? So, this thread serves a dual purpose of determining the merits of materials used to manufacture a lower, (and public opinion on the subject,) and possibly also to serve the purpose of identifying a standard to which AR's in general should be held. Thanks in advance, I'm looking forward to the results. Enjoy!
  2. DarkLight

    DarkLight Live Long and Prosper - On Hiatus

    Ok, so keep in mind that I'm not a metalurgist (sp?) by any stretch and that everything I know about Al is gleaned from the interwebs. That having been said, a couple of points to clarify my votes:
    • Right now I'd consider anything but polymer if it was in stock...and reasonably priced.
    • Generally, for a "sport" rifle, I would think that 6061 should be sufficient, because
      • the stresses exerted on a lower are, while not "minimal", generally not more than 6061 can handle
      • 6061 has better corrosion resistance
      • frankly, it's cheaper.
    Now, why might I consider 7075 over 6061. All other things being equal (even though they NEVER are), there's a reason that MIL-SPEC is 7075. Do I know what that reason is? No, and I didn't even stay at a Holiday Inn Express last night...however, I can come up with some reasonable assumptions:
    • Eugene Stoner was an aircraft engineer. Many (but certainly not all) civilian aircraft parts are manufactured out of 7075 and virtually ALL military aircraft parts spec 7075. It's what he used, day in/day out and was familiar with, which leads me to
    • Strength is a HUGE reason that the military specs 7075. It's stronger, it just is. Tensile strength, sheer strength, it doesn't conduct heat quite as well as 6061 (good for things that get hot if you aren't keen on the lower transmitting that heat to, say, your hand.), and believe I recall reading that it's slightly less electrically conductive (I think...I believe I read that somewhere but I am absolutely open to being corrected). With regards to strength, think of your buffer tower and try to remember the last time you cleared a jam (assuming you've ever had one) by smacking the rifle butt plate on the ground. Now, if you had a "strong enough" lower/buffer tower and a "stronger than it needs to be" buffer tower, which would you pick?
    • Depending on the QC of the batch, 7075 can be easier to machine because it's harder. I've read reports of 6061 not chipping properly and "birdsnesting" in the mill and gumming up the cutter on the lathe.
    • I've seen reports (third hand) that 6061 doesn't take anodizing as well or as consistently as 7075.
    There are, however, downsides to 7075:
    • It costs anywhere from 1.8 to 3 times as much as 6061
    • It is not as resistant to corrosion
    • 7075 actually melts at a lower temperature (although if your lower is hitting 470+ degrees C, YOU'RE DOING IT WRONG!)
    For most of us, I would think that 6061 would actually suffice, and that's not really fair. Suffice isn't quite the right word. Suffice implies that it's substandard (although for MIL-SPEC, it is). It's not like you had your heart set on a Ferrari but an Escort will suffice. More of a "wanted a sunroof but didn't want to spend the extra $3500" or incandescent is fine for headlamps although you kind of wanted the blue halogen.

    Me? I have a Bushmaster M4A3 Patrolman. It has a 7075 forged lower. I've probably put 1500 rounds through it and yes, at this point it's a range rifle. Would I put a .308 Lapua upper on it? Absolutely. .416 upper? Most likely. Would I put either a Beowulf or other (non proprietary) .50 on it? Maybe but I wouldn't make it my go to rifle at that point...there's a reason Barrett makes their lowers out of STEEL! Different topic for another thread though.

    This is a good brief comparison of many of the qualities of 6061 and 7075...and it's completely neutral.
    Compare Materials: 6061 (AlMg1SiCu) Aluminum vs. 7075 (AlZn5.5MgCu) Aluminum ::
    JABECmfg and Yard Dart like this.
  3. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    Alright, your math doesn't work. You have 4 votes and they each got 33.3 percent of the vote. That don't work.:(
  4. Yard Dart

    Yard Dart Vigilant Monkey Moderator

    My vote does not count.... biglaff
  5. NotSoSneaky

    NotSoSneaky former supporter

    FWIW I went with Billet and 7075. I Built my AR on a similar lower from Tactical Innovations. The only difference is the lower I used didn't feature a machined in triggerguard. The magwell is EDM cut and I've run a wide variety of aluminum, steel and polymer mags through it with very good results.
    JABECmfg likes this.
  6. DarkLight

    DarkLight Live Long and Prosper - On Hiatus

    I think the % is based on the number of respondent. I voted for two things and if it's the number of people as opposed to the number of votes, that would 'splain 33% for each one.
    kellory likes this.
  7. Brokor

    Brokor Live Free or Cry Moderator Site Supporter+++ Founding Member

    I just voted for Hello Kitty because it was on the list. [grlft]
    JABECmfg and Yard Dart like this.
  8. Jeff Brackett

    Jeff Brackett Monkey+++

    Back in another life, my father and I had a machine shop. We hit a bad slump in the '90s, and I drew on what I knew from a hobby of mine at the time (paintball) and my father's and my CNC skills to design an after-market paintball gun barrel. We made several prototypes from several different materials, including 6061 and 7075 T6. Some of the things I recall about working those materials:

    6061 was "gummy" to machine (didn't chip reliably) and often bound up the tooling. It was noticeably softer and scratched & dinged easier until hit with a good Type 2 anodize.

    7075 was much easier to machine, was noticeably more resistant to scratching and denting, but didn't take to anodizing as easily. Actually, now that I think about it, I don't think that last is quite accurate. It wasn't so much that it wouldn't take an anodize properly, but that it didn't take color anodizing as well. As I recall, a clear anodize worked very well, and produced a very scratch and dent resistant surface.

    So, in the "for what it's worth" department, those are my recollections on working with those materials. (And for the record, we ended up settling on 6063 T6 as a good compromise.) ;)

    PS - Wasn't sure, but thought I remembered that the reason for such a difference in machinability was a significant difference in metallurgy. Had to look this up to get the specifics. What I find is that 6061 is an alloy consisting of a blend of aluminum, magnesium, and silicon. 7075, on the other hand, is an alloy of aluminum and zinc.
    Last edited: Sep 28, 2013
    NotSoSneaky, kellory and JABECmfg like this.
  9. NotSoSneaky

    NotSoSneaky former supporter

    If I were to attempt a build from an "in the white" receiver I'd use Cerakote.

    I had a rifle and several mags Cerakoted and it's well worth the cost.
    JABECmfg likes this.
  10. JABECmfg

    JABECmfg multi-useless

    Took me a little longer than I wanted to get back to this thread, so "Bump..."

    Excellent input so far, glad to see that we were able to get both votes and discussion on the subject. Thank you all for the input!

    Still good stuff, DL. I did not know that 7075 is MIL-SPEC, and that's useful info.

    Same here, working at my Dad's machine shop back in the 90's is what got me started on my career path.

    [lolol] (JABEC's 5 year old daughter likes this) [winkthumb]
    Jeff Brackett and Brokor like this.
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