AR10/.308 AR Build knowledge thread.

[n517rv]

Here is some useful information for the Aero Precision M5 308 Builders. These notes were compiled after speaking to Angela at Aero Precision and also with Alan from SpringCo. This is a work in progress (both these notes and my build) so please help me correct any errors.

Lower Receiver

The specific 308 parts for the Aero Precision M5 lower are:

• Pivot Pin - AP M5 specific
• Takedown Pin - AP M5 specific
• Bolt Catch - DPMS 308 pattern
• Bolt Catch Threaded Screw (included with the M5 lower, needs 1/16" allen wrench)
• Buffer Spring - use DPMS 308 pattern carbine spring or SpringCo Orange
• Carbine Buffer - use DPMS 308 pattern carbine buffer (2.5")

There is no trigger guard required, so the remaining lower parts from any Mil-Spec AR-15 LPK would be:

• Receiver Extension
• Buffer Retainer and Buffer Retainer Spring
• Takedown Pin Detent Pin and Takedown Pin Spring
• Pivot Pin Detent and Pivot Pin Spring
• Bolt Catch Buffer and Bolt Catch Spring
• Trigger Assembly (Hammer, Trigger, Disconnector, Disconnector Spring, Trigger Spring, Hammer Spring, Trigger Pin, Hammer Pin)
• Safety Selector
• Selector Detent and Selector Spring
• Magazine Catch, Magazine Catch Spring, Magazine Catch Button
• Pistol Grip, Pistol Grip Screw (and washer)
• Mil-Spec Stock

BTW, I suggested again that they package up an M5 308 Lower Parts Kit that is "minus" the trigger group and pistol grip. Hopefully we'll see one soon.

Upper Receiver

The specific 308 parts for the Aero Precision M5 upper are:

• Ejection Port Cover Door - DPMS 308 pattern
• Ejection Port Cover Rod - DPMS 308 pattern
• 308 Barrel - DPMS 308 pattern
• 308 Barrel Nut - DPMS 308 pattern
• 308 Charging Handle - DPMS 308 pattern
• 308 Bolt Carrier Group - DPMS 308 pattern
• 308 Flash Hider - 5/8x24" TPI
• 308 Crush Washer

The remaining upper parts from any Mil-Spec AR-15 can be used:

• Ejection Port Cover Spring
• Gas Tube (appropriate length for barrel)
• Gas Block (appropriate size for barrel)
• Forward Assist Assembly Kit

[Plasman]

Here is some useful information for the Aero Precision M5 308 Builders. These notes were compiled after speaking to Angela at Aero Precision and also with Alan from SpringCo. This is a work in progress (both these notes and my build) so please help me correct any errors.

Lower Receiver

The specific 308 parts for the Aero Precision M5 lower are:

• Buffer Spring - use DPMS 308 pattern carbine spring or SpringCo Orange
• Carbine Buffer - use DPMS 308 pattern carbine buffer (2.5")
• Receiver Extension
  

These parts aren't really specific since you can either use an LR-308 system or AR-10 system irregardless of the receiver pattern.

[LRRPF52]

As to your BCG question:
The BCM gunfighter charging handle is compatible with both AR10 and AR308 pattern carriers. So that leads me to believe that their length is very similar if not identical. However their bolts are different. So you need to match your bolt to your barrel.

Armalite bolts are made from 8620.
http://www.armalite.com/ItemForm.asp...8-8f26512df4ae

8620 is obviously not milspec and I guess has had problems. (I have an Armalite BCG with my Noveske barrel in my MaTen)
http://www.ar15.com/forums/t_3_118/6...teel_bolt.html

DPMS brand bolts are made of Carpenter 158 with the carrier being made of 8620 (see specs in link below)
http://www.brownells.com/rifle-parts...prod43843.aspx
Rainier has these also, and I think they're a site sponsor so shop there. Ok looking at Rainier... they're in the middle of a site upgrade and my account seems to be gone and their site seems to be in flux... so.... maybe not there, or at least not today.

What's interesting is that JP sells low mass BCGs that are 9310 for somewhere around $450. JP doesn't really sell crap, but if they're wanting to move some products and C158 is unavailable, I could only imagine that they would go with the next best thing. But it is only just that, and not the actual spec.
https://www.m4carbine.net/showthread...er-158-Vs-9310
https://www.m4carbine.net/showthread...highlight=9310

I'm pretty sure the original Stoner AR10 bolt was made from 8620, which is plenty fine for the AR10 because the geometry is large enough to deal with thrust and high pressure without shearing lugs. Stoner and team designed the AR10 bolt, barrel tenon, and barrel extension around the 7.62x51 cartridge, and its operating pressures with a FOS of 2. Unlike the AR-15, which is not chambered in the cartridge it was designed around (.222 Remington), there isn't a problem with the AR10's engineering in this area.

I don't see any reason to use C-158 on the AR10 bolt, and I wonder if that is a typo on Brownell's page that was extrapolated mistakenly from an AR15 BCG spec .

[TheBelly]

I'm building a Megalithic Keymod rifle now. I'm using the Mega barrel and the Slash's heavy buffer and spring. When I did a test fit, all the parts lined up just fine. The go/no-go gauge worked, and it fit a factory loaded cartridge easily.

All I need now is my Geissele RR to get it completed.

[LRRPF52]

Someone stated earlier in this thread that with all the developments going on in the AR10 world, there really isn't a lot of incentive to try to part one together, and I have to agree with that. I've been dealing with AR10's since 2002 now, have owned Eagle Arms (re-named to ArmaLite Inc.), DPMS, and have had GA Precision do my last two based off parts before they did the GAP-10.

With what Colt has done with the 901, and Freedom Group/Remington (with the DPMS brand name) in the GII, I think everyone that is making SR-25 length receivers should seriously consider halting production, and going back to the 1950's AR-10 receiver length, which is actually quite short.

These large receiver sets make the guns unwieldy, mess up the length of pull, and while they were great over the past 21 years, I think their time has come. Colt approached the BCG length very simply, by just going with a shorter Bolt Carrier with tail material removed. The forward part of the bolt carrier is mostly based off an AR-10, and it has what appears to be a standard AR-10 bolt in it. When I say AR-10, I mean one of the originals. Colt was actually one of the original companies after the Dutch Artillerie Inrichtingen, and Fairchild ArmaLite to have an AR-10 design. Colt, having recently purchased the patents and licensing from Fairchild-ArmaLite in 1959, tooled up to manufacture what would have been the AR-10A, but it was not to be.

All 3 of these original designs had very short receivers that feel pretty much like an AR-15 in your hands. That is the trend that seems to be getting back into gear, which is how the guns should always have been. When Stoner worked with Reed Knight II on the SR-25, there was a need to make the SR-25 BCG fit inside of AR-15 receiver extensions, to minimize initial outlay in tooling for the new rifle.

We have now seen that a shorter Bolt Carrier will work, combined with the AR-15 RE tube in both the 901 and the GII. If I was influential with the other companies on the market, I would halt the super long receiver and BCG production, and go back to the way the gun was meant to be. The BCG is very easy to change by removing 5/8 tail material. The receiver set needs to be shortened in the rear with that awkward tang. The charge handle needs to be shortened as well. That's pretty much it. Many will complain that this adds more variation to the market. It doesn't matter, as there already is an endless minefield of parts variation for AR-10's.

As a fun DIY project, it would be interesting to make one's own upper and lower, with a cut-down bolt carrier in the tail, and CNC their own charge handle as well. Use existing barrel extensions and move forward from there like normal.

There is some basic mechanical engineering to be done with bolt travel and buffer length, mitigating the rail length of the bottom raceway guides of the bolt carrier so that you don't have impact into the RE tube threads that go forward along the top surface of the lower, just ahead of the RE tube ring/housing.

[Plasman]

All I need now is my Geissele RR to get it completed.

The Knight's tool is pretty much the same thing as the .308 RR and MUCH cheaper.

[Benito]

Someone stated earlier in this thread that with all the developments going on in the AR10 world, there really isn't a lot of incentive to try to part one together, and I have to agree with that. I've been dealing with AR10's since 2002 now, have owned Eagle Arms (re-named to ArmaLite Inc.), DPMS, and have had GA Precision do my last two based off parts before they did the GAP-10.

With what Colt has done with the 901, and Freedom Group/Remington (with the DPMS brand name) in the GII, I think everyone that is making SR-25 length receivers should seriously consider halting production, and going back to the 1950's AR10 receiver length, which is actually quite short.

These large receiver sets make the guns unwieldy, mess up the length of pull, and while they were great over the past 21 years, I think their time has come. Colt approached the BCG length very simply, by just going with a shorter Bolt Carrier with tail material removed. The forward part of the bolt carrier is mostly based of an AR10, and it has what appears to be a standard AR10 bolt in it. When I say AR10, I mean one of the originals. Colt was actually one of the original companies after the Dutch Artillerie Inrichtingen, and Fairchild ArmaLite to have an AR10 design. Colt, having recently purchased the patents and licensing from Fairchild-ArmaLite in 1959, tooled up to manufacture what would have been the AR-10A, but it was not to be.

All 3 of these original designs had very short receivers that feel pretty much like an AR15 in your hands. That is the trend that seems to be getting back into gear, which is how the guns should always have been. When Stoner worked with Reed Knight II on the SR-25, there was a need to make the SR-25 BCG fit inside of AR-15 receiver extensions, to minimize initial outlay in tooling for the new rifle.

We have now seen that a shorter Bolt Carrier will work, combined with the AR-15 RE tube in both the 901 and the GII. If I was influential with the other companies on the market, I would halt the super long receiver and BCG production, and go back to the way the gun was meant to be. The BCG is very easy to change by removing 5/8 tail material. The receiver set needs to be shortened in the rear with that awkward tang. The charge handle needs to be shortened as well. That's pretty much it. Many will complain that this adds more variation to the market. It doesn't matter, as there already is an endless minefield of parts variation for AR-10's.

As a fun DIY project, it would be interesting to make one's own upper and lower, with a cut-down bolt carrier in the tail, and CNC their own charge handle as well. Use existing barrel extensions and move forward from there like normal.

There is some basic mechanical engineering to be done with bolt travel and buffer length, mitigating the rail length of the bottom raceway guides of the bolt carrier so that you don't have impact into the RE tube threads that go forward along the top surface of the lower, just ahead of the RE tube ring/housing.

Yeah true. I am really hoping that .308 AR sizes and weights can be dialed back a wee bit, a la the DPMS GII. Who would have thought that DPMS would be setting a trend in the positive direction? The current .308 AR BCG's are pretty massive. Mind you, I am not a firearms engineer, so I cannot say if this is necessary given the cartridge. It seems to me that effects of shortening/lightening the bolt carrier can be offset by using a smaller gas port and using a stiffer action/buffer spring, no??

The Knight's tool is pretty much the same thing as the .308 RR and MUCH cheaper.

The description states that this only works with Knights SR-25 guns. For other .308 ARs, it seems like the Geiselle .308 Reaction Rod is the only game in town. Anybody know of any less costly alternatives??

On a side note, what the hell is with the shape of the barrel extension on SR-25's??? I though the only real difference with KAC barrel extensions was the radiused bult lugs.
db_file_img_107_720x720.jpg
This looks like a Mayan architecture.

[polydeuces]

.............. "Colt was actually one of the original companies after the Dutch Artillerie Inrichtingen, and Fairchild ArmaLite to have an AR10 design. Colt, having recently purchased the patents and licensing from Fairchild-ArmaLite in 1959, tooled up to manufacture what would have been the AR-10A, but it was not to be.
All 3 of these original designs had very short receivers that feel pretty much like an AR15 in your hands"............

I think this one or one like this?
Youtube video Miculek shooting DAI AR1O

[polydeuces]

COMPREHENSIVE RECAP.


REGARDING LPK's:
AR15/M4 parts are interchangeable (this includes springs/detents-please verify) with AR10/ AR.308 EXCEPT for:

• Bolt lock
• Take down pins
• Dust cover

Please Note: These are 'maker' specific - yet while they won't fit across AR platform, in some cases they will fit across AR308 makers.


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.
The VLTOR A5 system:
If a carbine type stock is preferred over a rifle (A2) RE one of THE best options hands down is the VLTOR RE10/A5 RE's.
This can be run with a rifle spring/H3 buffer, as well as the A5 set-up.


REGARDING BARREL AND BARREL PARTS:
Barrel has to be specific for either AR10 or AR308. (Or better said - the barrel extension)
Barrel nut specific for either AR10 or AR308 - non AR15.
For the AR-10 it is" 1-7/16"-18 TPI-3A
For the AR-308 it is: 1-7/16"-16 TPI-2A
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/Mid/Rifle), but again, some exceptions may prove to provide surprise. Again - verify when in doubt.

A side note, based on personal experience: since we're dealing with a combination of parts that may present a bit of an unknown quantity, running an adjustable gas-block with the VLTOR RE10/A5 RE is found to be the ideal combination for fine-tuning the rifle.
Where have we heard this before......


REGARDING HANDGUARD / RAILS:
Hand-Guards, traditional, are cross-platform and make. There is a good variety of offerings, keep the following in mind:
Rails: Must match the upper type.
Basically there are 3:

• AR10,
• LR308 (dpms) high profile) and
• LR308G2 (dpms) low profile.

Then some other variations to keep things interested - including but not limited to:

• SR-25 has a specific thread pattern and rail height
• 1996 ArmaLite Inc. AR-10 used the same dims for height and thread, IIRC
• DPMS LR-308 used SR-25 height, but different threads for the barrel nut
• Bushmaster BAR-10/RRA LAR-8 is another animal
• DPMS AP4 upper went with a lower rail height, and DPMS's unique barrel nut threads.

Again:
Barre nut threads:
AR15: 1-1/4"-18 TPI
DMPS 308: 1-7/16"-16 TPI-2A
AR10: 1-7/16"-18 TPI-3A


REGARDING BCG
While on paper 'The BCG' can be used across AR10/AR308, (non AR15) Beware! there is apparently plenty of exceptions to this rule - proceed with caution and due diligence.
Whether to look for Car158 or 9310 steel again is up for debate as well as a wide variety of finishes. No lack of choices there either.

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.

REGARDING RECEIVERS
As with all things AR some parts play well together some don't: Rule of thumb if one tries to save $$ - get quality parts on sale, not cheap parts with questionable pedigree. Getting matched receivers would be wise - same make or at least makes known to fit very well together.
Many have and still are purchasing "certain early production receivers" only to find out there's some major fit and function issues. Courtesy prevents me from calling them by name - but doing a search should provide ample info whether or not a make is GTG.



This should cover 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.

[Plasman]

The description states that this only works with Knights SR-25 guns. For other .308 ARs, it seems like the Geiselle .308 Reaction Rod is the only game in town. Anybody know of any less costly alternatives??

On a side note, what the hell is with the shape of the barrel extension on SR-25's??? I though the only real difference with KAC barrel extensions was the radiused bult lugs.
db_file_img_107_720x720.jpg
This looks like a Mayan architecture.

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.