View Full Version : Difference in AR15 lowers

March 6, 2011, 06:56 PM
I have one AR15 and have always been intrigued by building my own someday when I get some time just to say I did it. I have two brothers-in-law who both have multiple units with one always on the hunt for different upper and lower configurations. I know there are lowers with different triggers, match and two stage and those made from metal and others made of polymer but one one thing I don't fully understand. Some are stamped 5.56 and others are stamped "multiple" which I assume means multiple calibers. What is the difference?

I see prices all over the place from a $300 LMT to a $180 no name brand. He picked up an Armalite and we looked at a Spikes Tactical - what is the difference in the base of all of these.

Confused in Kansas.

March 6, 2011, 07:07 PM
The caliber stamping is irrelevant. "Multi" markings just recognize the variety in uppers that one might use.

As far as maker, so long as it is in spec (holes in right spots, no small cracks or voids), it is fine and purely personal preference. Big names tend to get more $, but that doesn't really matter.

Sent from my MB300 using Tapatalk

March 6, 2011, 07:38 PM
Some are stamped 5.56 and others are stamped "multiple" which I assume means multiple calibers

Have never run accross one yet. But that might change is the prices start to drop.

I would assume that the 5.56 lower is for a AR-15/M-4 rifle. Now as to the Multiple, I would believe it is for a AR-308 type rifle that can be made into a 243, 257, 260, 308, 450 or anything that uses a 30-06 as it's base case width. Heavier material for the additional pressures, longer mag well for the larger cases.

Just my guess.

March 7, 2011, 12:43 AM
Some AR lowers such as the S&W don't have caliber marked at all. Anyway, it's obvious whether the lower is an AR-15 or AR-10 version so marking Multi or a caliber or no caliber doesn't matter much, just choose the right physical size and the rollmark you like. Spikes is a good choice and can be found on sale under $100 often. A stripped ArmaLite lower retails for about $160 but can be found for about $120.

March 7, 2011, 09:04 AM
As far as I see it, there is little reason to buy a high dollar lower. The lowers that are from Aero Precision, such as Surplus Arms and Ammo(buy from AIM), or Palmetto State Armory's, which I have, are great. All holes line up perfectly, mates up perfectly, and least important, the finish is really nice.

Right now, I believe that the SA&A lower at AIM is $59.99; a steal anywhere!

March 7, 2011, 09:39 AM
I prefer the billet machined uppers versus the forged mil spec versions for the simple reason that most of the billet uppers have an integral trigger guard.

POF and Tactical Innovations manufacture nice examples.

March 7, 2011, 10:26 AM
I think that you meant lower, not upper.

They are a nice feature, but I'd rather put the money in ammo and have a forged lower that I can put a bigger trigger guard on.

That's the great thing about the AR, we can all have what we like!:D

March 7, 2011, 11:09 AM
Now as to the Multiple, I would believe it is for a AR-308 type rifle that can be made into a 243, 257, 260, 308, 450 or anything that uses a 30-06 as it's base case width. Heavier material for the additional pressures, longer mag well for the larger cases.


While there are two sizes of lower, the AR-15 sized ones (as opposed to the AR-10 sized ones for .308 and rounds of similar length) tend to be rollmarked "5.56/.223" or "Multi" (or variations on that theme). The multi marked ones just recognize that you could have anything from .22LR to .223 to .450 Bushmaster (just to name a few) sitting on top of it. It's the marking on the barrel that matters, not the marking on the lower.

The larger lowers for the longer rounds tend to be visually distinct- if you're used to dealing with the smaller ones, the enlarged magwell just sticks out like a sore thumb. They're also much more expensive.

So long as you're dealing with something in spec, it doesn't matter what is on the lower. There isn't even any reason to get a billet lower over a regular forged one.

It's entirely a matter of preference and what you're willing to pay for. I bought some Spike's lower from AIM a few weeks ago for $80 each. They also had some SAAs for $60 that would work just fine, it was just my own preference to go for the Spike's. I've also used CMMG lowers I've bought for $150 locally and a Superior Arms that was a shade less (not to mention an Aero Precision I have had sitting around for a while).

The only differences between them are the rollmarks and the Superior Arms lower has a slightly tighter magwell (earlier versions of Pmags won't drop free from it, but they work just fine). That's it.

There's no reason to buy a $200 LMT or Noveske lower over a $60 Surplus Arms and Ammo from AIM unless you just want that Noveske marking.

March 7, 2011, 11:09 AM
Essentially, lowers are a commodity item. The only thing required on them is the maker and a serial number.

I have an AGP lower, great machining, with an adjustable trigger overtravel screw, which really improves a milspec trigger kit. Cost me $80, there are others selling for less than $60 now.

It's marked multi-cal, made no difference to me, but it's under a 6.8SPC upper.

Billet offers little theoretical advantage other than custom shaping, forged lowers and uppers can be had in a wider variety, because forging dies aren't that hard to make - just cost justify. The exotic billet parts are all programming, they cut a chunk of bar stock, not machine a semi finished shaped part.

For a testimony of which works better, forged auto rims and forged auto pistons are preferred for high performance, billet is pretty much custom bling parts for dress up. If they rate large production, the makers will go to cast and save money, as CNC time isn't cheap.

Most billet parts use lesser grade materials, they claim the machining is better, but they always weigh more. For the same shape part, forged is always stronger and lighter. Armalite knew that, they parent company was making aircraft parts, it was standard until composites became available.

No billet for my guns or hot rods, please. It's all about looks, not performance.

March 7, 2011, 09:09 PM
Is there any major differences between these?

Thanks for the replies and company names. Keep them coming

March 7, 2011, 09:33 PM
Polymer is plastic, and therefore lighter. There have been very few makers churning them out (Bushmaster has their Carbon 15, but I think Cavalry Arms is now defunct). I've seen some strength concerns about the Bushmasters, but I don't know how much of an actual issue that is.

Personally, I think the only reason to go with poly receivers on an AR is for something of the absolute lowest weight possible. Lightweight barrel, lightweight handguards, etc. If you aren't going to keep with the "weight is the enemy" theme for the entire rifle, there's no point and you're better off just going with a forged lower- cheaper and easier to get your hands on anyway.

March 8, 2011, 09:33 PM
Personally, the only real difference worth considering is whether the lower has a lower rear shelf that will accept a registered drop in auto sear if you're lucky enough to find one and be able to afford and feed it.

Although Florida permits full auto my bank account doesn't, so I went with a RRA which has excellent fit and finish.

If I ever get the desire for a full auto gun, it will be an American 180 in 22lr. A far cooler gun that any 22 has a right to be.

March 8, 2011, 10:05 PM
The AR was designed to be made with aluminum, not plastic or carbon fiber. There have been some issues with these. It's not like other firearms with major components made of the same; they were designed around those materials, the AR was not.

Just stick with aluminum, and you can avoid any of those issues.