Added the 716.  Thanks for the input.

Stock Options (written by Spart)


Caveats

RRA LAR-8 and Bushmaster BAR-10 308 (pre-2010) caveat: these guns have a proprietary design with proprietary buffers.  RRA goes out of their way to state this on their website.  The design started life as the Bushmaster BAR-10 and the design was sold to RRA, who have continued marketing it as the LAR-8 it after making small changes.  Bushmaster has been selling rebadged DPMS LR-308's as the Bushmaster ORC and Hunter 308 lines since 2010, and this caveat does not apply to those rifles.  Bushmaster BAR-10 and RRA LAR-8 actions have a longer stroke, and thus a shorter buffer compared to every other 308 AR out there. Take a look at this picture of an LAR-8, the receivers are a bit odd (long) in proportion to most 308 AR's. The reason is the proprietary bolt catch/release, which is positioned similarly to an ACR or Beretta ARX.  Therefore nothing in this section is applicable to these rifles, however Slash does sell buffers for these rifles on his website.

DPMS GII LR-308 caveat: these guns have a new proprietary design, and according to DPMS their carbine buffer and spring do not interchange with the gen one rifles.  I assume that none of this information pertains to the GII rifles.  It could be that they have gone to a system that splits the difference between ArmaLite and DPMS in order to achieve a system that is 100% proprietary in nature, but that's just conjecture on my part.

HK MR762/HK417 caveat: The receiver extension on these rifles is much larger in diameter and completely different and incompatible with all aftermarket stocks because you suck and HK hates you.

Action length 308 vs. 5.56

The first thing you need to know is that AR-10 and 308 AR rifles have a longer action length than AR-15 rifles.  The actual action length isn't super important (and will vary even between rifles of the same make and model due to variations in the way the receiver and receiver extension are threaded) but it is important to know that it is around 3/4" longer than an AR-15 action.  This means that the BCG is moving an additional 3/4" into the stock, the charging handle is moving an additional 3/4" to the rear, and for these reasons you cannot swap an AR-15 stock, buffer and action spring system wholesale to a 308 rifle.  Many AR-15 parts can be used with 308 rifles when combined with the correct 308 specific components.

Rifle stocks

Rifle stocks for AR-10/308AR's are by and large the same as AR-15 rifle stocks.  Due to the longer action length, a stock with a cheek riser that works on an AR-15 may interfere with a 308 AR's charging handle.  Magpul sells a version of their PRS for 308 AR's specifically to address this issue, however the standard AR15 PRS can be modified by cutting the cheek riser, and I assume other stocks with adjustable comb height could be similarly modified.

Rifle buffers for 308 rifle stocks are not the same as AR-15 components, they are 308-specific. Standard(ish) 308 rifle buffers are slightly heavier and about 3/4" shorter than the AR-15 rifle buffer to accommodate the longer action stroke.  

ArmaLite EA1090 - Listed as 5.1875", 5.4 ounces
DMPS 308-BS-11 - Listed as 5.25", 5.4112 ounces
Slash Heavy Buffer - Listed as 5.200", 10.0 ounces.

Action springs for 308 rifle stocks are also not the same as AR-15 components.  They are higher rate springs.  Slash recommends the ArmaLite part FWIW.

ArmaLite EA1095
DPMS 308-BS-10B
TUBB ARBUFSR
JP JPS-OSR.308
JP JPSCS-10 - proprietary captured system with springs, must use included spacer, alternative springs available as JPSCS-PACK10
JP JPSCS-10K - as above with alternative springs, must use included spacer.

Carbine stocks

Here's where things get muddy.  There are two competing standards for carbine stock systems in 308 AR rifles, and it goes beyond the commercial/mil-spec dichotomy found in AR-15 carbine stock systems.

The first system, which I will refer to as the ArmaLite AR-10 style carbine stock system or "ArmaLite style system" for short, uses AR-15 carbine buffers.  As stated earlier, the stroke of a 308 AR's action (and thus the stroke of the BCG inside the receiver extension) is around 3/4" longer than in an AR-15, and so for this system there are 308-specific receiver extensions that are around 7 3/4" long internally vs. 7" internally on the AR-15 variety.

The second system, which I will refer to as the DPMS LR-308 style carbine stock system or "DMPS style system" for short, uses AR-15 carbine receiver extensions.  Again, due to the longer stroke of the 308 AR action, a 308-specific buffer is used that is around 3/4" shorter than an AR-15 carbine buffer.

This picture illustrates the difference between ArmaLite AR-10 style carbine receiver extensions and the AR-15 carbine receiver extension used in the DPMS style system:

http://i.imgur.com/zMb8y6a.jpg

This picture illustrates the difference between DPMS LR-308 style carbine buffers and the AR-15 carbine buffer used in the ArmaLite style system:

http://i.imgur.com/EPYhwpe.jpg

ArmaLite AR-10 style carbine stock system

ArmaLite and several other manufacturers (complete list at the bottom of this section) utilize an AR-15 carbine buffer in conjunction with a 308-specific action spring and receiver extension.   You can use any carbine stock that matches the OD of your tube (commercial vs. mil-spec) however see the notes below on which setups will either not fully collapse or over collapse.

The buffer ArmaLite uses is identical to an AR-15 H3 buffer.  It contains three tungsten weights and weighs 5.4 ounces.  Other manufacturers that use this system style may use differently weighted buffers from standard carbine all the way through H3.  If you need to go heavier than an H3, the AR-15 buffers listed on Slash's site will work and he recommends the XH.

Action springs are 308-specific and are of a higher rate than AR-15 carbine springs.

ArmaLite EA1095 - This is the same as for the ArmaLite rifle stock and is what I use in my carbine stock.
TUBB ARBUFSR
Sprinco "RED" Spring

Receiver extensions are 308-specific and are about 3/4" longer than AR-15 receiver extensions (see pic above.)  Depending on the receiver extension used, you can fully collapse elongated stocks such as the VLTOR Emod and MagPul ACS/ACS-L/STR stocks.  On the flip side, if you use a stock with no back (visible hole in the rear of the stock as with a mil-spec collapsible stock) it is possible to over collapse a standard length stock on an extension that allows an elongated stock to fully collapse.

Several manufacturers offer the 308-specific receiver extension for sale separately:

VLTOR RE-A5 - mil-spec OD, allows elongated stocks to fully collapse.
VLTOR RE-10/A5SR - mil-spec OD, will not allow elongated stocks to fully collapse or standard stocks to over collapse.
ArmaLite 10207025 - mil-spec OD, will not allow elongated stocks to fully collapse or standard stocks to over collapse.
POF 00517 Buffer Tube, Anti-Tilt (7-Position) - mil-spec OD, allows elongated stocks to fully collapse.  Anti-tilt feature for op-rod guns.
LaRue LT629-15C for 7.62 - Select the 7.62 option, mil-spec OD, will not allow elongated stocks to fully collapse or a standard stock to over collapse.

Incidentally, the non-VLTOR tubes will probably work with VLTOR A5 buffers in an AR-15.  I have not verified this, but I don't know why it wouldn't work.  Could be of interest to folks who want an anti-tilt receiver extension with an A5 buffer in an op-rod AR-15 - POF may have you covered.

Stocks are standard AR-15, and all of the receiver extensions I have found utilize the mil-spec diameter, so you'd have to use a mil-spec stock.  As mentioned above, if you choose the right receiver extension you can fully collapse an elongated stock such as the VLTOR EMOD and MagPul ACS/ACS-L/STR.  If you wish to use a stock with an open rear, make sure to choose a receiver extension that will not let you over-collapse the stock.

Complete stock kits are available from additional manufacturers that do not offer the parts individually:

KAC offers the "M110 Collapsible Stock Kit," part number 25951.  It's not listed on their website but you can purchase it through their dealer network, e.g. here.  This kit appears unique in that it utilizes a ten position receiver extension, whereas the other receiver extensions available are either seven or six position.  It appears to allow elongated stocks to fully collapse and comes with the MagPul ACS.

LMT offers a few different kits:

LMT L7LA2CT - I can only assume this is mil-spec OD since LMT's SOPMOD stock is mil-spec, the stock is not long enough to fully collapse.
LMT L7LA2C - As above only in black.
LMT DMR308-KIT - same guts as above but with LMT's DMR stock that resembles a MagPul PRS.  It slips on over the carbine style receiver extension whereas the PRS utilizes a rifle receiver extension.

The following rifle lines utilize the ArmaLite style system, albeit with their own flavor of buffer weights and springs:

ArmaLite AR-10
KAC M110 (when equipped with above-referenced kit)
KAC 16” SR25 EC and ECC, see here.)
LMT LM308
POF mfg Oct 2012 or later, see note at bottom of page here.
S&W M&P10 - known to use smaller gas ports and lighter buffers.  Rifle stock systems use the carbine buffer/spring and a spacer.
LaRue 7.62
PSA PA-10*
Sig 716 - certain models use the DPMS style system instead.
Ruger SR-762

* Apparently many if not all of the first PSA PA-10 rifles to ship came with the ArmaLite length tube, but the DPMS shorty buffer.  This caused the shoulder on the BCG to slam into the lower receiver and receiver extension causing damage.  Apparently moving forward, they are using the correct AR-15 length buffer and if you have one of the DPMS shorty buffers, you NEED to call them and get a replacement.  Your buffer spring may also be incorrect, count the coils and measure the length, should be about a foot long with 27 coils.  Because of this fuckery I can't recommend buying PSA parts, although their receiver extension might be an option in the future if you can get them to sell it by itself for less than what the other options on the market cost.

DPMS LR-308 style carbine stock system

DPMS and several other manufactures (complete list at bottom of this section) utilize an AR-15 receiver extension in conjunction with a 308-specific buffer and action spring.  You can use any carbine stock that matches the OD of your tube (commercial vs. mil-spec.)

The buffer DPMS uses looks like a cut-down AR-15 carbine buffer.  It is around 3/4" shorter.  You can see a comparison pic above.

There are a few options for buffers:

DPMS 308-CS-10B - this is the standard DPMS buffer.
Slash CAR-10 buffers - Available in 5.5oz and XH 6.5oz.  Slash recommends his proprietary spring for use with these.
Buffer Technologies KynSHOT KSRB5004 - Hydraulic recoil damper.
JP JPSCS-10 - proprietary captured system with springs, alternative springs available as JPSCS-PACK10
JP JPSCS-10K - as above with alternative springs.

Other companies may make something very similar to the DPMS buffer, but they've gotten pretty generic by now similar to mil-spec AR-15 buffers.

Action springs are specific to the DPMS LR-308 style system.  Springs that work in the ArmaLite AR-10 style system will not work with the DPMS style system.

DPMS 308-CS-10A
JP JPS-OSC.308
JP JPSCS-10 - proprietary captured system with buffer weights, alternative springs available as JPSCS-PACK10
JP JPSCS-10K - as above with alternative springs.
Slash .308 CARBINE Buffer Spring - Custom
Sprinco "ORANGE" Spring

Any AR-15 carbine receiver extension will work with the above components, commercial or mil-spec.  If you want to run a MagPul UBR on your rifle, they're the only way to go.

The following rifle lines utilize the DPMS style system, albeit with their own flavor of buffer weights and springs:

DPMS LR-308 Gen 1 Rifles
Bushmaster 2010+
Remington
POF prior to Oct 2012
Black Rain Ordinance
CMMG
Colt 901
Fulton Armory FAR-308
LWRC REPR
Wilson Combat .308
JP LRP-07
SIG 716 - certain models use the ArmaLite style system instead.

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