AR Lower Receiver FAQ (56k beware) MMS, CMT, LAR, LMT compared...

[xenophobe]

Receiver FAQ Version 0.1 (please note this is still rough, and is not nearly finished)

I live in a ban state, so no luck getting Bushmaster, Armalite, DPMS or Colt into the mix. My apologies.

I see a lot of threads asking about Quality and Suggestions for which brand of receiver any particular person would buy, so I thought I might write this info I've posted in a number of places to have it's own thread.

There are currently FOUR manufacturers that produce the majority of lower receivers for the AR market. MMS, CMT, LMT and LAR receive orders from many licensed manufacturers who obtain an ATF variance to have them cut and logo receivers on their behalf. JVP and Superior Arms cut for a couple of different companies as well, but currently I will only focus on the four main manufacturers differences.

Mega, Stag (CMT), LAR and Barrett (LMT):



Not all inclusive, and a few brands have had more than one manufacturer cut their receivers. Many companies receive CMT and LMT cuts in the white and finish them themselves. I have not seen a LAR or MMS cut that was finished by a third party company.

LMT = LMT, Lauer(old), DS Arms, PWA, Eagle, Knights Armament, Barrett, Bushmaster (?)
CMT = Stag, RRA, High Standard, Noveske, Century (current), Global Tactical, CLE, S&W, MGI, Wilson Tactical, (some?) Colt, Ratworx
LAR = Grizzly, Bushmaster (L Prefix), Ameetech, (?)DPMS, CMMG, Double Star, Fulton
JVP = Double Star, LRB
MMS = Mega, GSE, Dalphon, POF (forged), Alexander Arms,
Olympic = Olypmic, SGW, Tromix, Palmetto, Dalphon, Frankford, (old) Century
Sun Devil = Sun Devil forged billet receivers
Superior = Superior Arms, Lauer (current)
Grenadier Precision

Characteristics of the manufacturers (please note, the most typical characteristics are listed, and each manufacturer may have substantial sample variation between lots):

LMT usually leaves forge flash underneath the trigger well, and roughly cuts them between the receiver extension and pistol grip, while leaving a vertical mold flash line on the front lip of the mag well, as well as having other "fingerprint" marks... no bevel cut for the charging handle on the rear lug for the receiver extension, as well as particular mill marks in between the pivot pin tangs. They also have a 'fingerprint' cut in the receiver on the shelf, and below it where the FCG goes. Notice the diagonal mill mark on one of the pivot pin supports. Also unique is the radius in the grip tang pocket, which is not as smooth a transition as the other manufacturers.

[xenophobe]

CMT has a rounded bevel on the front of the mag well lip, generally removes the forge flash underneath the trigger well, usually offers a smooth and rounded surface between the receiver extension and pistol grip and has a unique mill mark that would be hidden by the attachment of a pistol grip. There is also a clamp mark of some sort that occurs on the top of the pivot pin lugs that LMT and LAR do not have (see 1st photo at beginning of thread).



LAR sometimes leaves forge flash underneath the trigger well, and does have a smooth flat milling mark on the round transition on the web between the receiver extension and grip. By the back of the grip tang, there is a milling mark that goes across the width of the receiver. The front of the receiver has a deep cut between the pivot pin retainers, and the front of the mag well is not always flat. The front radius to the mag well bevel is round, but the front edge sometimes shows forge flash.

[xenophobe]

MMS usually the cleanest cut, with the exception of some CMT receivers. All of the MMS receivers for Mega, POF, Gunsmoke, Dalphon and Stinger I've seen have the typical black teflon coating. Some of the receivers look absolutely perfect, others have mag wells that are cut from both sides and don't quite match up in the center. Some of them also have what look like file marks running in one direction on part of all of the receiver, and can be somewhat subdued or very noticable. I won't describe machining fingerprints, because all Mega manufactured receivers are pretty obviously made by MMS.



The forgings that CMT and LMT use are also from different manufacturers. The ribbed A2 strength on the reciever extension lug is thinner on the LMT, while the CMT is almost the full width. Mega appears to use the same forgings as LMT. All of the manufacturers seem to have some variation of mag well bevels, and those aren't primarily useful in identification.

From left to right, Mega, Stag/CMT, LAR, LMT and Barrett,

[xenophobe]

Other comparisons
All of the following photos will show from left to right; Mega, Stag, LAR, Barrett and/or LMT:

Notice the lack of a charging handle bevel on the Barrett/LMT


Notice the difference between the LMT and the larger mag well bevel of the Barrett (far right):


Trigger well forge flash clearly visible on the Barrett and LMT:

[xenophobe]

Links to the manufacturers:
LMT = Lewis Machine and Tool
www.lewismachine.net

CMT= Continental Machine and Tool
www.continentalmachinetool.com
www.stagarms.com (an individual corporation that was started by CMT)

LAR = some combination of the original owner's last initials
www.larmanufacturing.com
www.largrizzly.com

MMS=Mega Machine Shop
www.megamachineshop.com (new)

JVP=JV Precision
jvprecision.net

Superior Arms
www.superiorarms.com


Okay, I'm done for now... whew... More info and pics later.

If there are any corrections, or requests for pics/comparisons of angles I have not yet posted, please PM me.

[damon1272]

Xeno,
Great info. This will direct me in my next purchase.

[G17GUY]

Wow, great thread!

[NSR500]

Good Info! Thx...

[triggerhappy]

Thank you, thank you, thank you. That was very informative and will he quite helpful for my 1st OLL purchase

[tiger222]

xeno

thanks for the great pics and info....
not being a machinist ~ is there a clear winner here?

[SemiAutoSam]

You mentioned you didnt have a pic of an Armalite.

Here is such a pic at least of the Magwell area.



BTW Xeno as usual good work.

[kneedeep]

good write-up thanks for the pics.
whats the AR connection and backround in pics? good source of information?

[damon1272]

This thread should be a sticky.

[NeoWeird]

I quickly glanced over the posts, but by the looks of it Stag has the nicest and most uniform machining of the lot. You can really see this in the contoured edge between the grip and stock, also on the magwell where the wall width is nice and uniform and square, where as the others tend to have slight imperfections, small waves, non-square edges, etc. Also on the hood of the receiver extension tower (or whatever you would like to technically call it) you will notice a nice even flat where some of the others have mulitple plateau levels or are slightly angled.

Not saying the others are bad, but from the looks of these pictures, Stag would be my personal choice in regards to quality. YMMV.

ETA: Just throught I should add this note. The contoured edge between the grip and stock is most likely caused just by tooling. Most places probably just put a straight end mill in and come in close to get that edge off. Stag (and I think one other looked really nice as well) most likely have a contoured tool that is either shaped like a sideways U to the exact contour of the receivers contour, or it looks like a normal end mill with a round corner biten off the edge and they do one side, flip it over and do the other. Either way it's only effects it's aesthetic appearance and does not indicate that the other manufactures took shortcuts, were sloppy, poor machining, etc. It's simply just the difference between using two tools that do the same thing but one has a slightly nicer finish for this particular application.

[NeoWeird]

Here is a quick drawing to show what I was talking about for those that don't know much about machining. The receiver itself is usually taken from a rough casting. A piece of metal, in the case of the AR usually 7075 aluminum is pressed in a two piece mold to get all the outside contours and edges done. This process leaves a ridge along the outside of the reciever where metal is forced between the two mold pieces, this is usually about as thick as paper, but very near the actual receiver a thicker ridge is left, this is because of a slight contour on each edge of the mold, some from deburring the edge, some for stress reasons, others for easy removal from the mold. Once it is cleaned up to the rough casting it will look like this:



At this point the rough milling can be done, and all other processes like drilling, taping, etc. This forging process is why those billet lowers look smooth and shinny. See the forging crushes the metal to the form on the outside with great pressure. Small imperfections arise in the skin, but at the same time the skin is compressed and becomes super rigid. The outside does not need to be touched with anything as it is already to size, but on billet lowers it is machined from a single piece of billet (essentially just bar stock - a big chunk of metal in the shape of a long rectangle usually) so the entire outside needs to be machined. The result is a smoother and cleaner finish, but it doesn't get that surface compression. It most likely doesn't matter, but to some the surface compression is important, to others the finish is important. Either way billet lowers take more many hours and more tooling to make, so they are just inherantly more expensive (but that does not mean better).

Back to the point at hand, this is a crude diagram showing the difference between a contoured mill and a normal square end mill.



An end mill is like a drill, except it can cut on it's face instead of on it's point. So in the diagram above you can see how the square end mill removes the ridge, but leaves that flat edge behind where as the contoured mill removes the ridge to the edact contour of the receiver. Neither one is better, but the contoured mill will leave a much more pleasing finish as there will be no lines to see and it will be one smooth continuous line around the receiver. It's an exact tool, and exact setup/labor, so most companies probably don't want to deal with or don't have the ability to.

Again it doesn't do anything for the receiver outside of making it more aesthetically pleasing.

[catsupsam]

Thank you...you don't get enough credit for your work and postings regarding the differences in lowers.
This will show up over at ar15.com pretty quick...hope they will reference it.

[SemiAutoSam]

Anyone into metalwork ?

http://www.northeastshooters.com/vbu...2&d=1172710214

[hi_desert]

Very nice compilation! Question, all the receivers that I have purchased or seen recently, RRA, Stag, CMMG, and Mega, have no painted roll marks. Yours are all white in the photos. Is that your own custom touch or something that manufacturers use to do in the past. Thanks

[PLINK]

Originally Posted by hi_desert

Very nice compilation! Question, all the receivers that I have purchased or seen recently, RRA, Stag, CMMG, and Mega, have no painted roll marks. Yours are all white in the photos. Is that your own custom touch or something that manufacturers use to do in the past. Thanks

I am not sure what Xeno used but some people use Crayons or grease pens.

[goldfinger]

moderators, please sticky this

[artherd]

So, basically, what you're saying is that AR lowers are all about equal as long as everything fits, and they don't fall apart, right?

Nice comparison though, interesting to see some of the detail on how the machining practices differ.

[xenophobe]

Yeah, well all the AR receivers that I used for the demonstration all work equally well. There are differences in machining techniques and finishing touches, but all of them are just as fully functional as others. This post really only addresses the cosmetic issues of final machining.

I use art/drawing grease/oil crayons to fill in the markings.

[CALI-gula]

GREAT POST! And GREAT PHOTOS!!

However, just what are you trying to accomplish by laying them out atop a Ouija board??

You want to make them MORE EVIL????

.

[Mr. Ed]

Who makes Sabre Defense lowers? They're a military contracted company that makes nice rifles.

[jaymz]

Originally Posted by CALI-gula

GREAT POST! And GREAT PHOTOS!!

However, just what are you trying to accomplish by laying them out atop a Ouija board??

You want to make them MORE EVIL????

.

Beat me to it!!!

[stator]

Originally Posted by PLINK

I am not sure what Xeno used but some people use Crayons or grease pens.

China markers available in arts supply and office supply stores.


I should add that finish milling does not make a reliable AR. The only valid comparison is to take samples from the manufacturer and mic them. Or in other words, you want something as close to dimensionally perfect as possible before you start to worry about the cosmetics.

In mic'ing lowers for about 15 years now, I have found that LMT, and Colt are about the best, and LAR is about the worst on this list. I have not mic'd any MMS but these should be up there if milled from billet.

The question that I get all the time is how can one tell without bringing in a caliper to the gunstore and check a bunch of lowers? Well, the two best areas to look at are the magazine boss and the sides of the trigger well.

For the trigger well, just eye the side thickness. Sort out the ones with one side much thicker than the other. Move onto the magazine boss and look at how centered the mag catch slot is. I've seen some that barely pass through the boss.

Also, check the front pivot pin holes and how well it is centered in the front lugs.

[wheelgunner]

xenophobe, thanks for the great info.

Do you know who is making "Centermass Tactical" Calguns lower receiver?

Also, Moderators can you make this a "sticky"?

I first read this as a sticky" on AR15.com.

[SemiAutoSam]

From talking to the man that owns Centermass Tactical they are made in a shop in Carson City Nevada.

Originally Posted by wheelgunner

xenophobe, thanks for the great info.

Do you know who is making "Centermass Tactical" Calguns lower receiver?

Also, Moderators can you make this a "sticky"?

I first read this as a sticky" on AR15.com.

[supersonic]

Originally Posted by triggerhappy

Thank you, thank you, thank you. That was very informative and will he quite helpful for my 1st OLL purchase

+1 on zat. Man, you must have a LOT of time, not to mention you must smell like S**T!!!!!(being that you seem to be anal-retentive!) LOL...LOL... Just joshin', I couldn't help busting yer balls, mang! Anyway, great detail in those pics. I'm assuming you are the (proud) owner of the items in question.?
S.S.

[Dayton]

xenophobe this is amazing. I've always wondered the cosmetic differences between lowers. Thanks so much.

[Blacky]

This is probably the most useful AR Tip thread Ive seen.

Have there been enough manufacturer changes to justify any updates?

[Shane916]

Originally Posted by Blacky

This is probably the most useful AR Tip thread Ive seen.

Have there been enough manufacturer changes to justify any updates?

Not that im aware of


and the thread lives again!

[J_Rock]

IMHO these will be the best lowers ever created

Magpul billet lower:
did I mention its a billet
integral trigger guard
flared magwell
threaded bolt catch pin
basically this requires no roll pins what so ever to build

[Jicko]

Originally Posted by J_Rock

IMHO these will be the best lowers ever created

Magpul billet lower:
did I mention its a billet
integral trigger guard
flared magwell
threaded bolt catch pin
basically this requires no roll pins what so ever to build

For the record, NO MAGPUL lowers were ever sold.

You are probably not going to see it anytime soon, if ever, on the market.

[apbrian112]

great thread! just wondering if anybody knew who makes spikes lowers? i have 1 stag and 2 spikes lowers and the tolerances are slightly different. just wondering... thanks.
-brian-
ps. +100000 on making this a sticky, will prevent all the "which lower?" posts from multiplying like rabbits on viagra...

[Hopi]

We need a "walking zombies" smiley for these damn necro-thread posts!

[apbrian112]

Originally Posted by Hopi

We need a "walking zombies" smiley for these damn necro-thread posts!

haha... didn't realize this thread was soooo old ... hehe... nevertheless, good thread for the new guys...

[Hopi]

Originally Posted by apbrian112

haha... didn't realize this thread was soooo old ... hehe... nevertheless, good thread for the new guys...

Yes, this was/is a good thread......you know xeno has been quiet lately.

[Blacky]

ev·o·lu·tion (v-lshn, v-) n.
A gradual process in which something changes into a different and usually more complex or better form.

[caldude]

It may be an old thread, but a good one for us newbies. In looking at the comparison pictures, the Stag lower has much cleaner machining IMO, so I'd probably lean that way in picking up an OLL if everything else is equal.