AR10/.308 AR Build knowledge thread.

[LRRPF52]

This is a Dutch ArmaLite owned by one of my friends in Finland. After a decade of handling post-1993 SR-25 type AR10's, (which both the Eagle Arms/ArmaLite Inc. and DPMS are variants of in terms of engineering origins) putting an original AR-10 in my hands felt totally different.

There isn't anything awkward about them, and you immediately have the sensation that, "Hey, I could carry this bad boy in the field and like it." They are very well balanced, respond to input from you immediately, and are frighteningly accurate as well. The Dutch knew what they were doing, and the attention to detail on these rifles exceeds what we typically see in the US.

Examples include the radiused ejector face, which was hard chromed after the fact, the impeccable barrel work for a service rifle, and the dutiful manner in which they executed Stoner's design intent. This rifle printed under an inch at 150m, with iron sights using the magazine as a monopod in the prone, with South African 7.62 NATO surplus in my hands. I normally don't talk about the groups it is capable of because the BS flag would naturally come out, but I have to tell you that this particular rifle was a laser for me.

[LRRPF52]

If someone who has been around long enough to remember the developments of the AR10 type rifles since the SR-25 were to make a chart showing compatibility and interchangeability, unique parts, gas system lengths, pins, bolt catches, charge handles, receiver thread pitch for the barrel nut, hi rail vs. lo, extension tubes, springs, and buffers, ejection port doors, handguards, muzzle thread pitches, grip tang variances, and so forth, it would look literally like a Pentagon power point graphic that 20 people had collaborated on over a span of months, working at a feverish pace.

This chaotic variation in the AR10 market has also launched an after market, not only for handguards, but for gas system lengths. There is no standard gas system length with AR10's, and there are barrel makers who index the port location based on their understanding of where it should be, even though they have no connection to KAC, ArmaLite Inc., or DPMS. You might ask for a "standard" RLGS, and get one that requires a unique gas tube length. I'm dealing with this right now with a buddy's Krieger-barreled AR10 built on Iron Ridge billet receivers. He asked for standard RLGS, and got the one that requires an ArmaLite Inc. 15.5" gas tube, but he put the tube length he thought he had ordered on it, which is the same on the AR15 RLGS: 15 1/8". DPMS uses 15 1/8", whereas the ArmaLite Inc. rifles use 15 1/2". The gun short-strokes of course.

That's just for starters. It would require financial resources to document all the variations that exist in the post-1993 AR10 world. This is why for my custom projects, I bought a matched receiver set and BCG, and sent them off to someone who had a reputation for knowing what they were doing with AR10's. I got back functional, super accurate rifles that have been trouble-free, other than the fact that with my .260 Rem. AR10, if I fire it from an ejection port door closed condition, it will sometimes induce a stove-pipe as the action beats the spring's ability to get the port door cleared before the case hits it.

One of the biggest things you can't control when going the DIY route with AR10's is the chamber, and what reamer was used, unless you are a machinist/gunsmith who will source his own extension, blank, and reamer to make sure it gets done exactly as you would like. The biggest and most reputable names in this business have had problems with getting correct reamers, because of the nature of reamer making in this industry. Unless you demand certs, and check your reamer with an optical comparator to the print you sent, you are placing your complete faith in the hopes that you are getting what you asked for, which is less often than one would expect.

Along with pressure containment vessel metallurgy with the bolt, barrel extension, and barrel, the next set of critical dimensions are your gas system, which is very much conditional on the chamber specs-a fact often overlooked by DIY types. Then comes the gas port location and diameter, the gas block, the tube, the carrier key and its metallurgy and finish, the manner in which it is fastened to the carrier, and the critical geometry of the carrier inside, then out. Then comes gas ring dims and metallurgy. A lot of companies think they are getting over right now by doing NiB, then calling it a premium BCG.

In the budget market, every component I just listed is cut corners on to slash costs at every opportunity, because "the customer will never know". This is why an LMT, LaRue, JP, or KAC rifles costs what it does. ArmaLite has been able to drive their costs down, but I think they offer one of the best bangs for the buck if you are happy with an obese receiver set from the post-1993 era.

Either way, we're going to see an explosion of "My AR10 doesn't work" threads with this new wave of cheap receiver sets and parts kits. It has already begun. The very first batch of beta-tester customers for the PSA PA-10 and Aero Precision M5 builds is having all sorts of issues, starting with fit and non-compatibility, to extraction and gas system troubles. These are direct symptoms of what I described above: No standardization of parts, bad reamers, corners cut, incorrect gas system dims and arrangement, and an overall lack of centralized ownership of the AR10 design.

[SomeOtherGuy]

@LRRPF52: a VERY interesting post, thank you.

[caelumatra]

Plasman and I are working to put something together that should be pretty comprehensive. But it's going to take a little time.

[Sticks]

Plasman and I are working to put something together that should be pretty comprehensive. But it's going to take a little time.

Understatement of the year.

[caelumatra]

Brief Comprehensive Recap.

Regarding RE/Stock set up:

In a nut shell, any type of RE can be used across the AR15/AR10/AR308 platform, regardless of make.
Be it M4, Rifle, A5 RE
What has to change/modified/adapted is the spring, and buffer size shape and weight - dependent on the type of RE.
The RE also obviously determines the type of stock that can be used.

This is correct.
The DPMS LR308 buffer will fit in a standard AR15 RE. And the spring must match

The AR15 H3 buffer can be used in the AR-10 (RE-10 from Vltor) RE. And the springs must match

Regarding the Barrel and Barrel Parts:

• Barrel has to be specific for either AR10 or AR308.
• Barrel nut specific for either AR10 or AR308 - non AR15. (please verify)
• Gas block is completely identical across platform/make - obviously dependent on barrel size/seat.
• Gas - tube completely identical across platform /make - obviously dependent on op. system (Car VS Mid).
• Hand-Guards, traditional, are cross-platform and make. (please verify).
• Rails: Can be used across AR10/AR308 BUT dependent on Upper receiver - whether it is Hi-profile, or Low profile. non-AR15 (please verify)

Barrel or LR308 G2. The threaded extension area on the g2 upper is shorter and this would obviously cause many problems. However as noted below about uppers, not a lot, if any makers of G2 barrels.
http://www.thefirearmblog.com/blog/2...ms-308-gen-ii/ (graphic about half way down)

Barrel nut Thread patterns are as follows (Store links below in the quote):

For the AR-15 it is: 1-1/4"-18 TPI
For the AR-10 it is" 1-7/16"-18 TPI-3A
For the AR-308 it is: 1-7/16"-16 TPI-2A

http://www.ar15.com/archive/topic.ht...f=121&t=628380

Gas tubes may be proprietary to the barrel. But the barrel description will say what it is. My earlier Noveske had an intermediate which is a non standard length, but it came with the gas tube. But I have seen most of the new ones are going towards standard lengths.

Rails must match the upper type. There are 3. AR10 and LR308 (dpms)(high profile) and LR308G2 (dpms)(low profile.) Plasman pointed out to me only one manufacturer selling G2 uppers. Adams arms seems to be the only one at present who makes a G2 upper. However there are several mfgers out there who sell G2 (dpms low profile) rails. Troy, MI, Samson and maybe a few more. Key thing is to check to make sure your upper and rail are the same pattern. If it says "DPMS" and makes no mention of G2, it's worth a phone call to verify but, it is more than likely DPMS high profile. If you have a G2, your upper is different, as well as numerous other things including your BCG.

Regarding BCG

The BCG can be used across AR10/AR308, non AR15. (please verify)

Possibly. And this is a little muddy. My reasoning for this is the JP BCG. The description of the JP BCG states that it will work in both BUT that the bolt is not interchangeable between carriers. My interpretation of this is that while the lugs and whatnot up front may be the same the bolt dimensions further back where it interacts with the carrier are dimensionally different and incompatible.

http://www.jprifles.com/buy.php?item=JPEB-308MP

The .308 version is compatible with the JP LRP-07 and the DPMS LR-308 platforms (or clones thereof) only and cannot be used to replace bolts in the Armalite AR-10 platform (or clones thereof).

http://www.jprifles.com/buy.php?item=JPBC-4SPAHP

With the Armalite/Rock River family of large-frame receivers, this assembly can only be used as a complete bolt carrier assembly group. Interchanging individual components will result in an unsafe configuration. DO NOT under any circumstances mix and match components between the platforms. Only use the complete JP bolt carrier assembly in the Armalite/Rock River platforms.

Not sure on this. But until we can verify, buy a BCG that matches the pattern of your barrel, just to be sure.

Note also that the G2 BCG is not compatible with basically anything and the rifle as a whole seems to be the least compatible with anything else on the market. That could be why no one is making anything but rails for it.

Regarding Magazines:

These are AR10/AR308 specific - AR10 needs dedicated magazine, whereas magazines for AR308 are compatible across makes.(PMag, SR25 etc)
HOWEVER: the new generation AR10 (AR10A) will accept certain non-AR10 magazines.


I think this covers what is relevant to most of us doing a build from scratch - there will be other variances with manufacturers but this is mostly when looking at complete rifles.
If anything here is incorrect, needs additional info and for requested verifications please let me know via PM and I will edit - trying to keep it short and comprehensive.
Thanks.

I can't find it but either you mentioned or someone else did that the ejection port cover will work ar15 to ar308 and this is not correct. Since I can't find it, maybe it wasn't in your post.

https://www.rainierarms.com/upper-parts-kit
https://www.rainierarms.com/upper-parts-kit-308

The ejection port cover and pin will be longer on the 308. The spring may be interchangeable but I don't know. I can look when I get home.

[caelumatra]

Understatement of the year.

Ha, you're not wrong lol

[caelumatra]

snip

While I dream of a day when Colt is the standard I fear it never will be. With the lawsuits Armalite went through to get "AR10" back they are NEVER going to fall in line with Colt. And since .mil is already invested in KAC with the M110 I see an uphill battle for Colt on this front. I would love it, but I just cant fathon KAC, Armalite, DPMS, Aero, Mega... all of them retooling their whole lineup to fall in line with Colt. I wish it would happen, but I doubt it ever will.

The most we could hope for (but wont happen) is for Colt to start selling their new rifle for around $997. If consumers bought nothing but Colts because of the interchangeability and price then it might force the others to do something. But even then probably not.

[polydeuces]

Add to this that Colt may be out of business before too long.....

I understand an earlier stated concern that with the utter lack of standardization reliability may seem somewhat unobtainable.
Though....going with my experience building AR15 platform rifles in any given configuration I learned using reputable established makers and and vendors a large portion of that can be eliminated. Knowing where to spend the money is important as is knowing which parts play well together.

Also understanding that functioning is on occasion a delicate balance between gas system, gas-port diameter, buffer weight and action spring-rate is helpful, (did I mention forget to mention BGC....?) as is actually enjoying solving that puzzle if and when these issues arise, learn and share.

All of this is why we are communicating - right here and now.

[Benito]

It works with LR308, SR-25, and AR-10 barrel extensions. Operationsparts says it is in their description and I've used it on a bunch of non-SR25 rifles.

The tool is shaped like that because it has to also fit into the SR-15's E3 barrel extension which is of smaller diameter. The rear tines are used for the .308, the forward ones for the 5.56.

Yes, you're right. The description on Operationsparts does say that. The original link didn't mention anything other than the SR-25 though, and neither does the KAC website, http://shop.knightarmco.com/ProductD...ductID=KM30447.

Do you know if this is compatible with the Armalite AR-10A?