Need advice on a 308 AR build

[motox917]

I'm currently in the process of building a 308 AR. I've built some AR-15's already (2-5.56 and 1- 300 blackout), but I'm a complete novice when it comes to .308 AR's. So far I have:
Quentin Defense 80% lower
CMMG lower parts kit
buffer tube, buffer, and buffer spring
DPMS Upper receiver (with forward assist and ejection port cover)

I'm planning on getting the following for the upper:
Mega Arms 18" barrel (http://www.riflegear.com/p-1998-mega...08-barrel.aspx)
YHM low-pro gas block (http://www.riflegear.com/p-886-yanke...gas-block.aspx)
Mid-length gas tube (http://www.riflegear.com/p-440-gas-tube-mid-length.aspx)
Standard birdcage flash hider and crush washer

Will the gas block and gas tube work for a .308 AR?
How are the Mega Arms barrels in regards to quality and performance?

Thanks in advance

[FMJBT]

The YHM lo-pro block and standard mid length gas tube will work on that setup. The gas tube may require a slight amount of "tweeking" on the dogleg bend of it to get it to line up perfectly with the gas key, due to the larger diameter of the BCG on a 308 placing the gas key slightly higher. I haven't had to do this on the 308's I've built, but have read that it can be an issue on some.

Also, for the gas block I'd suggest going with an adjustable unit rather than the standard lo profile non-adjustable. Of the 3 AR 308's I've built, every single one of them has ended up being overgassed. On a 5.56, overgassing is not a huge deal, it just causes some components to wear a bit faster. On a 308 though, the heavier BCG coupled with an overgassed system results in significant increases in recoil. My 16" mid length 308 was absolutely brutal until I put an adjustable block on it.

I went with the SLR Rifleworks DA-7 adjustable block. It's design allows for adjusting it from the front without the need for a seperate locking screw to tighten down after adjusting, or the need for an extra tool to depress spring plungers during adjustment:

http://www.slrrifleworks.com/index.php?route=product/category&path=70

[bsumoba]

you could also go with a JP adjustable gas block. those seem to work well and they have so lo-pro versions as well.

Just curious if you're going with 18" for any reason. weight? I would recommend a 20" barrel if you can handle the length and slight added weight. it'll give you more options, especially if you're running this more as a SASS style rifle. Plus, I think with a 20", you can run a rifle length gas system, which from what I hear, is a little more reliable and in keeping with the original design of the Stoner AR-10.

With the DPMS upper, I would recommend NO forward assist. Go with a delrin plug. Saves a little weight, less "parts" to deal with and, in reality, who uses the forward assist?

CMMG LPK is gtg. I think this is what I have on my 308 build.

NO experience on the mega arms, but there are a lot of proven barrels out there and I am sure most of them are gtg. I chose a JP 20" supermatch barrel because it also comes with a headspace bolt, but was deciding between that, a Noveske or Fulton.

I don't see a BCG in there, and would urge you to look at JP or Fulton or DPMS.

[motox917]

Alright thanks for the info guys. I'll definitely go with an adjustable gas block. I planned on going with an 18" barrel/mid-length gas system to keep the rifle somewhat compact, but another member PM'ed me and recommended going with a 20" barrel/rifle-length system so I'll go with that. The only thing that's keeping me from getting a JP barrel is money. I want to get a good barrel but these 308 guns are so damn expensive to build haha

I'm currently going to school full time and only working 3 days a week at the most, so I'm trying to build this on a tight budget.

[97F1504RAD]

Get your barrel here and save some money, that's where I got mine. I also went with the 18" and they have them in stock.

http://www.jsesurplus.com/ar308.aspx

I have been in contact with Mega on this same topic and they recommend the Syrac Adj Low Profile gas block, which can be found at Rainer Arms

http://www.rainierarms.com/

[CCTFAS]

If you need we have these in stock now and to help you out on pricing here is discount code for 10% off. If you decide to go with one of our barrels just type tenpercent when it asks for any discount codes during checkout. Link is below for all the specs on the barrel.

http://www.cctdefense.com/store/pc/CCT-Defense-20-308-Rifle-Length-Match-Grade-Barrel-149p591.htm#.UnMB1Pm-1I4

[Cedone12]

Tagged! Lots of good info so far! Thank you OP for asking this question!

[Syds Grandpa]

Your not going to find a lot of 308 barrels in stock right now unless they're on the pricey side. We are buying 18 inch Black Hole Weaponry barrels and are real happy with them. These guys are great to deal with and they have inventory. It's a Polygonal Barrel. So do your research. We've achieved outstanding accuracy with them. And they are affordable. If you go direct right now their lead time is 12 weeks.

http://www.surplusammo.com/ar-308-parts/

[FMJBT]

I didn't realize that you didn't already have a barrel. I suggested the adjustable gas block based on the mid length system of the 18" Mega barrel. A rifle length system on an 18" barrel would largely negate the need for an adjustable block due to the lower port pressure and shorter dwell time. I would suggest this barrel for a good combination of long range capability and relatively light weight:

http://www.fulton-armory.com/barrelfatitan185nmmedss1x10936gasblock.aspx

[jbatzmaru]

18 mega barrel are gtg. check out my build in my signature. just took it out to angeles this past monday.