Help with my first .308 build - KAC SR-25

[jamesbern]

We got lucky here in CT and a local dealer were able to score some new, never used, pre-ban SR-25 receiver sets. Picked mine up from the shop today. This is my first .308 AR build and want to make sure it's done right. I already know i'm planning on going with a 16" or 18" barrel (leaning towards the 16").

My main question is i've seen some parts listed as Armalite or DPMS....am I correct in the understanding that with the Knights receiver I should be looking at Armalite compatibility?

This is sort of what i'm looking to replicate:

http://www.knightarmco.com/wp-content/uploads/2012/02/2012_ECC_Right1.jpg

http://www.knightarmco.com/wp-content/uploads/2014/01/sr25e2apc_one.jpg

I'm very happy considering the new laws here we can't just go buy an AR, unless it's a pre ban.

[Plasman]

My main question is i've seen some parts listed as Armalite or DPMS....am I correct in the understanding that with the Knights receiver I should be looking at Armalite compatibility?

This is sort of what i'm looking to replicate:

http://www.knightarmco.com/wp-content/uploads/2012/02/2012_ECC_Right1.jpg

http://www.knightarmco.com/wp-content/uploads/2014/01/sr25e2apc_one.jpg


There are a few different areas of a .308AR that can use either LR308 (DPMS) or AR-10 (Armalite) pattern parts and you may want to use some of each on the same gun.

The main areas you need to be concerned with are the buffer system and barrel/BCG combo. All components of the buffer system must be of the same pattern (all LR308 or all AR-10), and likewise, BCG and barrel components should match.

For your build you may want to use an AR-10 pattern buffer system and LR308 BCG/barrel. The AR-10 buffer system is cheaper to optimize, offers more margin, and is true to the original design. LR308 BCGs and barrels have better availability and support.

Buffer parts I recommend:
-VLTOR A5 7-position receiver extension (if using a stock that can fit all seven positions, get 6-position A5 extension otherwise).
-AR-10 action spring
-H3 buffer (or PWS H4 buffer).


Unfortunately, it doesn't look like you'll be able to get a hold of an SR-25 URX-4 (not released for sale yet), but you can buy the SR-25 URX 3.1.

[jamesbern]

I appreciate the info. So if I understand correctly this barrel and BCG would be OK together.

Rainer Arms 16" barrel
https://www.rainierarms.com/?page=shop/detail&product_id=2688

DPMS .308 BCG
http://www.brownells.com/rifle-parts/bolt-parts/bolts/ar-308-bolt-carrier-assembly-parkerized-prod43843.aspx

____

As for the buffer system...I was leaning towards this:

CAR 10 buffer
http://www.heavybuffers.com/ar10carbine.html

308 carbine buffer spring
http://www.heavybuffers.com/springs.html

*With this setup I believe I can use my standard AR mil-spec 6 pos. carbine buffer tube. I then plan to install either a Magpul or my B5 Sopmod stock.

Now as far as LPK, are there differences between 308 and 5.56? I have a couple CMMG LPKs sitting around from my AR15 builds. I heard the bolt catch is different.

[Plasman]

I appreciate the info. So if I understand correctly this barrel and BCG would be OK together.

Rainer Arms 16" barrel
https://www.rainierarms.com/?page=shop/detail&product_id=2688

DPMS .308 BCG
http://www.brownells.com/rifle-parts/bolt-parts/bolts/ar-308-bolt-carrier-assembly-parkerized-prod43843.aspx


Correct.




As for the buffer system...I was leaning towards this:

CAR 10 buffer
http://www.heavybuffers.com/ar10carbine.html

308 carbine buffer spring
http://www.heavybuffers.com/springs.html

*With this setup I believe I can use my standard AR mil-spec 6 pos. carbine buffer tube. I then plan to install either a Magpul or my B5 Sopmod stock.

Yes, that setup is LR308 pattern and is for use in an AR-15 carbine receiver extension. I still recommend going with the AR-10 pattern though since it's cheaper, uses standard AR-15 carbine format buffers, and, according to Knight's, is better for the action spring (the LR308 pattern practically binds the spring upon compression). Knight's, Armalite, LMT all use AR-10 pattern buffer systems.




Now as far as LPK, are there differences between 308 and 5.56? I have a couple CMMG LPKs sitting around from my AR15 builds. I heard the bolt catch is different.

They're not quite the same. The differences are receiver pins, magazine catch, and bolt catch. You'll want the AR-10 specific bolt catch (better than the LR308 one and compatible with all formats). You also may want a spacer if your grip has a beaver tail.

[jamesbern]

Thoughts? PSA AR-15 on left and Armalite AR-10 on right.

I can't cycle the DMPS BCG with the Armalite catch in. Angle is too steep. Options:

1. Grind/sand it down so it isn't as tall (the "ramp" would end up being slightly round)
2. Install AR-15 catch
3. Order and install DPMS LR-308 catch and hope it works.

http://i78.photobucket.com/albums/j98/jamesbernatchez/866a7592-d2d0-4ff6-8a98-a03c65c64221_zps841be31a.jpg


On another note, I got the lower complete. Just waiting on the Knights trigger guard.

http://i78.photobucket.com/albums/j98/jamesbernatchez/2E4634BA-16FC-495A-B71A-20CE1BE972FF_zps0thutrog.jpg (http://s78.photobucket.com/user/jamesbernatchez/media/2E4634BA-16FC-495A-B71A-20CE1BE972FF_zps0thutrog.jpg.html)