[Kellen]

Sorry in advance if I'm posing a question that is rudimentary for most of you, but I'm trying to get up to speed on the differences in 308 upper receivers and seeking some knowledge share. Been looking across the internet and coming up short when it comes to informed answers. What I'm observing is that there are at least three different kinds of upper receivers for 308s. Do they have names? How did these differences originate? Why? We don't seem to have this misalignment problem when it comes to 5.56 NATO semiautos, so not sure how this came to be a problem with 308s, but any help you may provide to clear up the confusion would be appreciated. To help illustrate, shown below are pictures depicting three different kinds of 308 upper receivers I've observed (for all I know there may be others):
Example 1 (note the rear takedown pin is not on the arc of the rounded fit)

Example 2 (note the rear takedown pin is at the beginning of the arc of the rounded fit)

Example 3 (note that there is no longer a rounded fit, but an angled fit)

 

[ChaZam]

It gets to be a bigger mess all the time. Hence I've never waded into the AR10 swamp yet...
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https://308ar.com/articles/compatibility/

 

[SUBMOA]

The .308/7.62 platform is a completely different platform from .223/5.56 .
Requires a whole new lower as well as a upper but does open the possibility of other calibers as well. Time for a new rifle .

 

[FN FAL]

The AR 10 platform as far as I know has never had a MIL-SPEC designation and as a result we have a silly amount of slight variations. My first foray into the 308 platform I picked up a Rock River LAR8 very slightly used from a guy who's wife went bazerk after finding out he had spent $$$$ on a gun. For me it was meant to be as it is one that uses FAL mags instead of the DPMS style. Since I have bought a couple parts sets and 80% lowers in the DPMS config but haven't put them together yet. Too many things to do..

 

[Ron Eagle Elk]

Most AR-10 platforms are proprietary. They want you to buy their lower AND upper, so they are made slightly different than their competitor's version. There are aftermarket options for most of them, but you have to buy stuff that will fit your particular AR-10.

 

[runfiverun]

the AR-10 [Armalite-10] preceded the M-16.
everyone else just come along and screwed it up 40 years later.

pick a company and stick with it.
Noreen, Armalite, Stag, etc.

 

[Dutch]

Chiming in just to reaffirm what everyone else already said. It's similar a bunch of pistol clones where the parts aren't quite interchangeable, but they all look and function about the same. You just have to know which one you have.

Palmetto State will be around for a while, they would be a good option for an AR-10. The .308 I bought from them is excellent.

I've built a lot of AR-15's but I bought my AR-10 as a complete rifle. That's not quite true, I ordered the complete upper and the complete lower from Palmetto at the same time though. If I decide to buy a different caliber upper from Palmetto later I can be reasonably confident it will fit my lower.


Edit to Add - it's not a silly or uninformed question. Especially considering the almost universal interchangeability of AR-15 parts.

 

[AK Hunter]

AR-10s are not Mil-Spec like the AR-15 is never have been.
You have to match upper to lower. Some uppers even if the pins match the charging handle will be too low.

 

[jwrauch]

One of the reasons I haven't jumped into the 308 AR's.

 

[Kellen]

Dang. That's really a drag. I was unaware that the 308 semiauto platform wasn't standardized and the different manufacturers just did their own thing. Pretty ludicrous, no? That seems to blow hell out of my ambition to get a 6.5 Creedmoor complete upper for use on an existing Adams Arms 308. Unfortunately, Adams Arms doesn't offer a complete 6.5 Creedmoor upper. I also forwarded an info request directly to Adams Arms, but they haven't responded for some time now (maybe the virus is the cause). The closest match I found, going just on visuals (and let's face it, on-screen visuals aren't worth diddly), is from Rock River Arms, but they said their uppers only fit their own lowers, not Adams Arms. Guess I'm screwed....

 

[runfiverun]

you could [maybe] get one of their uppers and put your own barrel on it.
I'd be inclined to get a 260 rem. upper myself just to simplify bolt and magazine issues.

 

[Dutch]

Dang. That's really a drag. I was unaware that the 308 semiauto platform wasn't standardized and the different manufacturers just did their own thing. Pretty ludicrous, no? That seems to blow hell out of my ambition to get a 6.5 Creedmoor complete upper for use on an existing Adams Arms 308. Unfortunately, Adams Arms doesn't offer a complete 6.5 Creedmoor upper. I also forwarded an info request directly to Adams Arms, but they haven't responded for some time now (maybe the virus is the cause). The closest match I found, going just on visuals (and let's face it, on-screen visuals aren't worth diddly), is from Rock River Arms, but they said their uppers only fit their own lowers, not Adams Arms. Guess I'm screwed....

I would push on Adams Arms to see about getting an upper. I see they sell complete 6.5 Creedmoor rifles, surely they can make you an upper. I'd be surprised if they didn't want to sell you an upper.

If that doesn't pan out, your AA-10 does have value. It might be time to swap over to a different manufacturer.

 

[ChaZam]

Dang. That's really a drag. I was unaware that the 308 semiauto platform wasn't standardized and the different manufacturers just did their own thing. Pretty ludicrous, no? That seems to blow hell out of my ambition to get a 6.5 Creedmoor complete upper for use on an existing Adams Arms 308. Unfortunately, Adams Arms doesn't offer a complete 6.5 Creedmoor upper. I also forwarded an info request directly to Adams Arms, but they haven't responded for some time now (maybe the virus is the cause). The closest match I found, going just on visuals (and let's face it, on-screen visuals aren't worth diddly), is from Rock River Arms, but they said their uppers only fit their own lowers, not Adams Arms. Guess I'm screwed....

If you can ascertain what pattern of lower receiver that Adams uses, then you can locate a source for an upper that is compatible with that pattern of lower receiver. It's possible that Adams uses a proprietary lower of their own design, but it's also possible that they use the Armalite pattern, or the DPMS Gen I pattern, or maybe the DPMS Gen II pattern. If for instance they happen to use DPMS Gen I pattern lowers then you could buy a compatible upper in 6.5 Creedmoor from some other brand or vendor that also uses or sells stuff for the DPMS Gen I. Other brands use the DPMS Gen 1 Pattern besides DPMS. That could be anyone such as JSE Surplus, Palmetto State Armory, Midway USA, Primary Arms, or many other choices. Or if you find out what pattern their lower is you can round up all the appropriate parts to assemble an upper...

 

[ChaZam]

Info at this link might help you. Compare your Adam's lower to the pics of the LR-308 and the AR10 and see if that gives us a clue about what pattern the Adams rifle is built on.
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https://monstrumtactical.com/blogs/guides/what-is-the-difference-between-an-ar-10-and-an-lr-308

 

[Txhillbilly]

Most of the aftermarket Large frame AR's are based off the DPMS Gen 1 platform,and a few support one of the Armalite platforms. All you need to do is make sure the parts that you buy are for whatever platform your Lower and Upper receivers are made for.

It's not that hard to figure it out. It's kinda like buying parts for your car/truck,most Ford parts won't work on a Chevy. You gotta buy what fits your stuff,it's not generic like an AR-15.

 

[jerry]

Have a pic of your lower?

 

[Kellen]

Have a pic of your lower?

Hi Jerry. Mine resembles the "example 2" in the picture series included with the original post. Even though it's a 308, that pattern also most closely resembles the AR15 style. Here's a pic, but the image quality is not as good as the commercial picture. Hopefully it works. Thanks for your help.

 

[Kellen]

Oh, for crying out loud! Sorry Jerry, I didn't read your post clearly and sent you the upper pic. Here's a pic of the lower. Guess I need another coffee....

 

[ChaZam]

Oh, for crying out loud! Sorry Jerry, I didn't read your post clearly and sent you the upper pic. Here's a pic of the lower. Guess I need another coffee....
View attachment 140592

That looks like the DPMS Gen I LR-308 pattern like in the link I posted in comment #14.

 

[Kellen]

That looks like the DPMS Gen I LR-308 pattern like in the link I posted in comment #14.

Thanks Chaz! Just having a way to describe it is leagues beyond where I started.