I've built dozens of AR's including my High Power Service Rifle Competition guns, but now I would like to build a .308.  I see some of the uppers and lowers and lower parts kits are not compatible.

So, where should I begin?  I'm looking for an upper/lower (no barrel) that match, and use standard AR-15 trigger parts.  Thoughts?

TIA

IBTPSA

Decide on the platform first. AR10 vs DPMS. Many/most parts are not interchangeable between the two, particularly barrels (the barrel extensions are different).

Then pick your receivers and go from there.

Or pick your receivers and let that decide whether you go AR10 or DPMS pattern.

Keep in mind that there is no "mil-spec" standardization in the large-frame ARs, no matter which platform you choose. You have to do a lot of research to check parts compatibility before you buy, and even then you might have some trial and error with compatibility.

Most AR15 trigger groups will also work in "AR10"s.

clarification inserted.

Armalite is also characterized by the angle-cut receiver extension upright, as compared to the DPMS round quarter-circle cut.  in addition to the afore-mentioned differing barrel extensions.

buy same-brand uppers as your selected lower, to insure mating fit.  if you're going with a niche brand, i'd get several stripped uppers to insure you have a good supply for future builds, you know, just in case...

Get a LaRue Ultimate Large Frame kit and don't look back.

Order your lower from them once you have the upper purchase code.

LaRue Upper Kits

Order an upper and 80% lower from Genesis CNC.  If you order it this week you should have about 9-18 months to figure out the rest of the parts you want for your build.

I'm not sure what this means...

Thanks for the advice and clarification!

Do the PMags work in both?  I had a RRA .308 that used FAL magazines and wasn't a fan.

I like the 80% option, but 9-18 months is a bit long for me.  Are their other 80% options you would recommend?

I was being a bit facetious about the wait time- that being said, I’ve heard others gripe about waiting months on end.  I ordered and upper & lower from Genesis on backorder about two months ago and am currently waiting on production.  They are producing lowers now and are supposed to be getting uppers into their machine “soon after.  I haven’t used their products yet, but word is that they are good.

I have seen other 80% .308 lowers here and there and have not been impressed with any really.  Hopefully my experience with the genesis upper, lower, and jig will be positive and well worth the wait.

Ascend Armory has amazing quality receiver sets. Very good looking too.

that was in before the palmetto state armory

I feel that psa is a good building point. getting an upper and lower from psa, even complete is a solid start and then swap out parts as you decide to upgrade.
DPMS type was also easier to find barrels for.
and yes they use pmags.
Don't buy the cheap brownel ones. D&H also work well.

but my research was more about how cheap I could start out vs say most accurate, or lightest.

do you have an particular goal in mind? or just want an ar in 308?

I build big blocks on the Aero Precision M5 platform.

I am a big fan of their "Enhanced" upper receivers, in particular.  Makes building the upper a breeze.

They are very good quality and inexpensive.

Goal: 16" or SBR .308 for Hog hunting with 1-8 Primary Arms scope

If you want the most parts availability I would go with the Aero M5 receiver sets.  They use a DPMS high cut receiver.  All regular AR15 triggers fit and Magpul 7.62 PMags fit.  I am working on one right now.

I prefer 80%arms lowers, they are gen 1 DPMS.  No problem finding uppers. And cmmg lpk.

This really is the best option available right now. Just wish they offered Mlok as well. Think that would look sleeker, but whatever.

You can get it all in pieces so you build it. You know everything will work together because it all comes from the same source, and the recipe has been thoroughly tested. Only issue youll run into is tight parts that need workin.

Definitely what I plan on doing in the near future.

Its either that, or buying a complete Armalite DEF10, and swapping what you feel like.

Lots of misleading info out there, and in here. Its bolt face depth that makes headspacing issues, NOT the barrel extensions. These are almost identical, enough so to interchange between AR10 - DPMS style. Its the chambers used coulpled with bolt face depth that causes issues. Then you have gas port location AR10 - AR15/DPMS, Armalite being a tad long on midlength and rifle length needing Armalite Ar10 gas tubes or equivalent. DPMS uses AR15 length for commonality, AR10 used the longer ones to use USGI style plastic handguards.

This doesnt take into account how all these companies offering receivers, bcgs and barrels, are getting things to their own specs, and nothing is really shared or standard. Were at a point where alot of things work together sometimes, but not every time. Nothing is guaranteed.

Even with some companies, getting everything under one roof doesnt help. Because they are sourcing their parts from whoever has them in stock, and not everything is the same. QC lacks EVERYWHERE, and we the customers are left with shit, and going through bullshit to get our parts replaced. The industry is counting on us to either never really test these systems far enough to experience these known issues, or just accept them when they do. So they "get away" with selling crap for the most part. Thats what my tin foil hat says anyways.

That LaRue Kit is the way to go, even if you want to get it for a different lower than theirs. You got the critical components all together, your only worry will be the lower receiver being milled correctly. If you dont get one from LaRue that is.

There is no mil-spec for large frame ARs so the two patterns are DPMS and AR10. I almost always suggest sticking with the DPMS pattern unless you are doing some form of retro build. Parts availability and compatibility is much more user-friendly with DPMS. From there you need to decide on receiver sets. With the 308 patterned builds I stick to using like-branded sets, such as Aero. This will insure compatibility between the uppers and lowers.

As for handguards you need to be sure your handguard height matches your upper receiver. There are two heights in the DPMS patterns, high and low tangs. High is .210" height and low is .150" height. If you mismatch these then your receiver to handguard heights will be different. BCG must be a DPMS pattern for whatever chambering you use. (308 and 6.5 Creedmoor use the same BCG).

Most Milspec AR15 triggers will work. I tend to stick with ones that advertise usage in a 308 pattern.

Your recoil system is going to be the most confusing part in my opinion because there are so many different configurations. You can utilize a standard AR15 Milspec tube however you must be sure to use a shortened 308 pattern buffer. A normal AR15 buffer will not work unless used in a longer tube that will allow for it. There are various combinations you can utilize. This is the most comprehensive documentation on this subject. https://forum.308ar.com/topic/10133-buffers-receiver-extensions-stocks-and-springs/

It is not necessary but I prefer using an adjustable gas block in all my large frame builds due to the finicky nature of them at times. Bolt catch breakage issues are a thing with the large frames, mostly due to AR15 catches being used. Slowing down the recoil system through use of a heavier buffer or limiting gas will help alleviate this, as well as using a catch of upgraded material like the one offered from V7.

I'd go with the Aero receiver set, it's excellent quality, dpms pattern, nicely priced which saves more for a great barrel and optics.  standard AR lower parts kit except for the takedown pins and bolt catch and you are set.  I'd look at wilson combat with a matched bolt

If I built a new one right now:

1)2A Armament receiver set(it's lightweight)
2)Criterion 16" barrel with rifle gas
3)Fulton Armory BCG
4)Adjustable gas block(SLR or Superlative)
5)Whatever DPMS pattern rail you want that will accommodate the gas block

Everything else is interchangeable

Or be a rebel and get a slant cut receiver set like Stag's but use a DPMS barrel and bolt carrier group.

I think what people are trying to tell you is start with an upper and lower from the same manufacturer. If you can buy the upper, lower, and rail you will be even better off. Aero is probably the easiest and quickest for this if you aren't looking to do a lightweight build.

That barrel with lightweight receivers will have a noticeable forward weight distribution.  Balance will be atrocious.

Lightweight isn't the be-all, end-all.  Balance trumps all.

The barrel is only 39 oz, so not very heavy compared to other 308 stainless barrels. I think it would be fine with a sopmod or UBR stock and full weight bcg to balance it out

ETA: a magnified optic will also add weight to the receiver area to further balance it out

2A makes an awesome receiver set

A UBR, and you're concerned about half a pound of weight difference costing several hundred dollars in the receivers?

If you want a gimmicky receiver set, by all means want it and recommend it all you want.  But don't sit there pretending a few ounces will make a difference worth spending the equivalent of a couple hundred rounds of ammo on to everyone.  

OP could get THREE stripped M5 uppers and lowers for the price of one 2A set.  and one could easily save that 8-ish ounces (and a HELL of a lot more) just by using an FX-3 6x42 leupold in an aero mount, as opposed to the latest 30-power tactical buzzword scope.  

Hey ferret, calm down. I have plenty of aero receivers and they are fine. I was stating what I would use based on the changes I would make if I built another LR308. I have a 16" with a 1-8 scope like the OP wants and it is heavy in the middle of the gun.  If your philosophy on cost/benefit is different, neat.

Dave,

You can find used 16-inch Armalite AR-10 carbines on Gunbroker for about $650.  I'd get one of those, put in a Geissele, and shoot that sucker until you need a new barrel.

Then I'd buy a rifle-length gas Criterion (or have a cut barrel turned and chambered by your favorite AR smith), swap the standard nut and rail for an SLR, and go forth from there.

NICE! This is exactly what I'm after!

Great idea!

Buy a PSA upper and lower, have the 18" barrel shortened 2" by John Thomas at Retro Arms Works, then add stuff you like.

Buy a POF revolution and have an AR15 platform ar10!

I'm keenly interested in whether, or when your Genesis 308 receivers are actually in your hands.  next month, next year, whatever.  AFAIK(?), they have the market cornered for the Armalite-pattern angle-cut 80% lowers.  Thanks!