I'm thinking about building an AR in .308 Win so I am glad to have found this forum.  I'm also an engineer so I analyze everything then analyze my analysis.  Here is some information I have gathered about manufacturers and materials.

MMS = Mega Machine Shop
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.

LAR = LAR Manufacturing
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.

LMT = Lewis Machine Tool Company
They make a .308, but their website does not mention the Aluminum alloy they use.  The OP listed them as the source for Bushmaster rifles and Bushmaster says theirs are 7075-T6 Aluminum.

CMT = Stag Arms (?)
They use 7075-T6 Aluminum and don't seem to make a .308 version of their uppers or lowers.

DPMS = Panther Arms
They make a .308 using 6061-T6 Aluminum.

Armalite
They make a .308 using 7175-T73 Aluminum.

POF = Patriot Ordinance Factory
They make a .308 using 7075-T6 Aluminum.


About Aluminum alloys:

6000 series are alloyed with magnesium and silicon, are easy to machine, and can be precipitation-hardened, but not to the high strengths that 7000 can reach.

7000 series are alloyed with zinc, and can be precipitation hardened to the highest strengths of any aluminium alloy.

Temper designations

-T6  Solution heat treated and artificially aged
-T7  Solution heat treated and stabilized

6061-T6 alloy has good mechanical properties and has good weldability.  It has a yield strength (Fy) of at least 35,000 psi.  Weldability is why it is used in aircraft structures, automotive parts and bicycle frames.

7075 is strong but has less corrosion resistance than other AL alloys.  It is more expensive than 6061.

7075-T6 has a yield strength (Fy) of 54,000 - 67,000 psi.  This is why receiver manufacturers say their 7075-T6 parts are stronger than others.  7075-T6 is slightly more  susceptible to corrosion due to prolonged exposure to water or water vapor.  This has the effect of reducing the strength slightly, but the average AR user is not likely to experience this unless your weapon spends the winter at the bottom of a pond.

7075-T73 has a yield strength (Fy) of 51,000 - 54,000 psi.  This difference is due to a slightly different tempering process.  It results in a 7075 alloy that is nearly as strong and has better corrosion resistance than -T6.  That's probably why Armalite uses it.

But wouldnt you want the new machine work reandonized, IIRC the soft aluminum would be tend to corode?

And what of C3 Defense?
http://www.c3defenseinc.com

Not a lot of information on their web site.  I like the idea of a locally manufactured lower.  The basic, milled, black lower was going for $149 at a local gun show.

Alf

ps  Thanks for all the great info.   Very helpful.

Originally Posted By ramcdaniel1:
Originally Posted By fadedsun:
Is it possible to have a high shelf milled to be a low shelf? I'd love to purchase a RDAIS.


Yes it is. Basically the shelf is milled to lower shelf (Colt AR-15?) specs. There are machinists drawings available on the net for free and pay. Email me and I'll send you a free set I gleaned from it.

HTH

Robert


But wouldnt you want the new machine work reandonized, IIRC the soft aluminum would be tend to corode?

__________

Aluminum doesn't corrode or Rust like that. It gets just a little surface oxidation. I don't think that it would be anything to worry about really.

-Eric

Great info, thanks for posting it.

Any idea who produced the ardell lowers???

DEL-TON is a decent lower, but hard to say if it worth more than a RRA.  Milling is good, decent.  Finish is also good, takes oil well and darkens to a sharp black, like most other lowers in this class.  How does it mate up with another upper?  Mates well with RRA and Bushmster uppers from my experience.  Magwell has nicer flare than RRA or BMI.  For $89ea for a stripped Del-Ton lower, I can't really complain, and I have 3 of them.

Nothing to do with DIAS compatibility. Its the height of the flat area inside, just behind the safety and under the rear takedown pin.



But I can tell you that recent production RRA lowers are all low-shelf and therefore DIAS compatible.  My RRA lowers have serial #'s that start with "KTxxxxx..." and are all 2009 production.

I am not sure if this is the right thread to ask away, so please feel free to delete or move my post:

I have recognized that some lower receivers have a drain hole in the "fence" where the front pivot pin spring and detent is located, and others don't.
Mostly you do not see this on photos as the dustcover covers this part of the "fence". See the pictures for the difference.

Can someone tell me which lowers have the hole and which don't? Is it a question of manufacturer or A1/A2 specification?

Thank you! Mike

I do know that:

- Bushmaster (based on my pre-2004 production lowers): Yes, they have that hole.  

- Rock River (based on my 2008-2009 production lowers): Yes.

- Del-Ton (based on my 2009-2010 prod lowers):  Have to check, will let ya know.

- LAR (based on my 2009-2010 lowers): Will let ya know.

- AERO Precision (based on my 2010 lowers): Yes.



I'm more tempted to call it a vent hole than a drain hole.  I realize water and liquids can get in there, but if you fill it with the right grease, not much liquids will get in.  I don't think its "to spec" if its missing that hole, but maybe someone else can vouch for that.  All the schematic drawings I've seen show that hole.



FYI (I know this could belong in the Builds Forum) - When I build a stripped lower, I'll lube every detent spring with Tetra-Gun Grease before inserting the spring and detent into its hole.  This goes for the Pivot and Takedown detent springs, selector spring, bolt catch spring, and buffer retainer spring.  The Tetra-Gun Grease is  a "Flouropolymer Penetrating Heavy-Duty Grease Lubricant, which tells me it can withstand heat & degradation, and prevent corrosion.  I've had a tube of it for over 12 years (I bought several tubes in bulk back then) and the grease hasn't degraded or deteriorated at all.  And it allows my lower to function just like it should when it should.  So for long term storage and near-term field use, this grease works.

AGP arms machines their own lowers I don't know what forgings they use they need to bee added to this thread.

I searched through the whole thread and did not see anyone mention Sharps Mil-Spec Lowers. How do they stack up against what is mentioned here?



K

Add Lancer Systems?

I just checked my lowers.

spikes with bullet marking, upper shelf  

Del-Ton, lower shelf

Stag, lower shelf

Surplus, upper shelf

Surplus had the key hole forge mark still on it

never seen that before

I am not sure if this is the right place to ask, but I am desperately looking for info: For a project I need help getting exact gauges of the "fence surrounding the mag well" on a Colt AR-15 lower receiver (please see the pics).Good close-up ics would help too. I have access to a German OberlandArms OA-15, but the fence looks much sharper/angular shaped on that one. I am using a locally made surplus lower, and the fence at the front looks too big. I would like to machine it so it would look more like the current Colt lowers. If someone can post close up pics, especially of the front lip, that would really help. Is the shape of that fence the same on civilian and Govt issued military lowers? Any help is highly appreciated. Thank you! Mike from Germany.

What is the difference in billet and forged lower receiver other than price?

I would like to know as well.

Forged are cut from a blank that is sort of pounded and pressed in to shape like the one in the top of the pic, Billet is just that, thay are cut from a big block (or Billet) of aluminum stock(the one in the pic on bottom has been cut from a block).
Note how the basic shape is "forged"(or pressed) on the top one but it has been "Cut" By machine on the "Billet" or milled on the bottom.

Thx, are there reasons why one would be better than the other, besides cost?

coming up next.......
never ending debate.

Do a seach (or Post a question) in the tech forums.

Link

Link

thx, the second link was a better explanation as to the differences.

Does anyone know the quality of the S&W lowers?  I can't find any info on their site about much about the material they use.

New to the forum but old shooter.  The info has answered a lot of my questions.

Thanks

OUTSTANDING PIECE OF WORK.
Thanks to everyone who contributed and updates with new info from time to time!

My Olympic Arms lower (purchased 2003) has a low shelf.

Thanks to all for the infos

Does anybody have a current list of brand names and who is machining them as of May 2012?  I'm curious about Surplus Ammo and Delaware names in particular.
Thanks.

I hate to break it, but that list couldn't be farther from the truth.  The companies that do all of the machining don't advertise and don't want their names mentioned.  LMT machines for LMT.  Mega wasn't even around in 2007 and CMT is Marks dad (Stag owner).

Bottom line is the majority of the lowers out there either meet or exceed the military prints.

Anyone know anything about JD Machine? Upper or lower shelf?

AR shelf examples
According to these pictures, the 4 Aeroprecision lowers I have are definitely low shelf.  Purchased 3 in late 2011-early 2012 and one in mid 2012.  Serial # range for 3 of the 4 is US39xxx.  The 4th is US46xxx

Nice comparison pics! Thanks to everyone who contributed .. this is a great thread.

Which is the Second receiver from the left, in the 5-receiver line ups?

Great pics and information.  I have two RRA rifles.  One is CMT and the other is AV(Brass Aluminium Forging Enterprises in Ferndale, Michigan).  Both are well made and have excellent milling and finish.  The AV receiver is much harder then tne CMT, my son is a geologist and hardness tested them with his machine.  I was wondering if the hardness of the AV was good or bad as a receiver quality.  I always stamp the inside of my receivers before I add them to my collection and I could'nt even scratch the AV receiver with my carbide stamp.  Any thoughts would be appreciated.  MWallace

find a "Marksal Paintstik" all purpose cold surface marker- its a solid crayon type stick which fills the engraving and the excess can be wiped off. comes in various colors
Markal Company 250 N Washtinaw Ave, Chicago, IL.60612

Thanks, Great info

I am selling Anderson AR lowers that are standard Mil-spec at a price that not many can turn down. I open my business to educate and help promote the black rifle era. We have First production runs at 89.00 and Seconds lowers for 68.99. I am not certain if there are any other deals like this in the US. But as long as I make a little money, I am happy!


Gunmeisters.com

859-918-6734

KY state residents only unless I ship to FFL in your state of residence.


All stripped lowers are considered as a pistol unless otherwise identified as a rifle by Manufacture. JUST THE LAW Sorry.

We are located in Burlington,Ky 41005

You may wanna read a little more on the rules/laws of selling certain firearms.  The only firearms that a licensed dealer may sell to a person under 21 or out of state res. is a completed long gun (guns w/ a butt stock, no pistol gripped shotguns).    A stripped lower is a stripped lower and must only be transfered to persons 21 y/o + and to a res. of your state (if you're a dealer).  ATF doesn't care if XYZ Mfg. sold the stripped lower as a "rifle only" receiver.  If you are a private ind. you may sell pretty much anything to someone who is 18y/o + and a res. of your state.

Can anyone tell me anything about these lowers:
http://www.aimsurplus.com/product.aspx?item=F1AR57SL
AIM Surplus is selling them right now.  It looks like the receiver is marked "AR57" near the trigger group.  Additionally, the "AR FIFTEEN" logo looks very similar to the "AR FIVE SEVEN" logo on the 5.7mm uppers.

All of Sabre's parts afre built "in-house". I live about 20 minutes from them (well since they got in trouble it's pretty quiet) but the fit and finish on Sabre's is second to none. I love mine.

All of my receivers are low shelves.

Bushmaster:  L19XXXX, L22XXXX bought in early 2000-2001

DPMS:  F11XXXK and F12XXXXK bought in 2007-2008

Aero Precision:  US22XXX (have a few) bought in 2010

Delaware Machinery:  L003XXX (have a few) bought in 2012  (Beautiful smooth machining.  Much better than most.)

Ron

ANY LATEST UPDATE ON "WHO MILLS FOR WHO"?

Lauer Custom Weaponry lowers-   Both Superior and LMT have done lowers for Lauer.  Easy way to tell the difference, look at the serial number prefix.  "SML" is an LMT lower, and "SMS" is a Superior lower.  

On a side note LMT refuses to run any 'non-LMT' stamped lowers for anybody until they are caught up with their own, so that's going to be a LONG, LONG, time.

I was wondering if anyone know about the Ruger SRs, and if they are high or low shelf.  I do know that the underside of the uppers are milled for the auto sear, but I'm not sure how to tell on the actual lower.

Was this answered and I just missed it?  I am considering one of the lowers but can't really find anything about them.

Hey guys I have a Stag Model 2 AR that I bought a couple years ago, and I am comfortable enough with it now that I have decided to build my own. I was out at a local gun store today and they had American Tactical OMNI stripped lowers for 56 bucks, I got one. I was just wondering if there were certain uppers and LPK's that worked better with the polymer OMNI lowers. Like I said this will be my first build so I will probably have a bunch more questions later on down the road, and I don't plan on getting anything else major for a while. Maybe just a few little things for it, It will mainly be for target shooting because my other rifle will be my main one.
Thanks,
Brady

Where does Tacticle Machining out of Florida  fit in here? They do 100%, 80% for themselves, but do they do any for other labels? Are they forged?

I have a TacMac "TM-15" lower.  And they do machine their own, from Cerro forged blanks.  No billet.    
Low shelf, no tooling marks, great mag well flaring, but the finish mars easily.

Yeah, i realize you asked this last December, but i just built two that i bought at a local retail shop for $99 each, and im pleased with them!

Tactical Machining does over 140 other brands lowers (Only a 40 part minimum) and only sells uppers to two bigger brands since they take them all. All AR 15 type lowers and uppers are 100% mil spec forgings.

All TM .308 products are 7075 Billet and a new .308 is being set up this week for a marking variance customer on a brand new Doosan 4000 series horizontal mill.