Jump to content
308AR.com Community
  • Visit Aero Precision
  • Visit Brownells
  • Visit EuroOptic
  • Visit Site
  • Visit Beachin Tactical
  • Visit Rainier Arms
  • Visit Ballistic Advantage
  • Visit Palmetto State Armory
  • Visit Cabelas
  • Visit Sportsmans Guide

SI Defense Build


Recommended Posts

Finally, after over 14 months of planning, and gathering parts, I got my AR308 built. The whole project was a positive experience and I plan to do it again. There were so many people on this forum who helped with advice and an enthusiastic willingness to help me spend money. Thank you all.


The parts list is:

SI-Defense matched upper/lower


DPMS standard buffer and buffer spring

Bison Armory 20” black Cerekoted barrel

Bison Armory Intermediate length gas tube

Syrac clamp on adjustable gas block

Magpul MOE buttstock

Magpul MOE Plus pistolgrip

Apex 15” freefloat handguard

Shadow Ops NiB BCG

Knight’s Armament BUIS

Tac Ops Ambi charging handle

Griffin Armament 7.62 Tactical compensator


I had a couple design criteria for this my first AR308 build. First, accuracy and reliability: required. It better go bang on each trigger pull and give me <1.5MOA with the iron sights. To that end, I kept it pretty much off-the-shelf for the majority of the parts. Second, I wanted a clean, uncluttered look. I’ve seen too many gaudy ARs that look like they were built by the Transformers on LSD. Third, I was shooting for 8 lbs total weight. Didn’t make it, but more on that later. Lastly, I was aiming for a total cost of $1500-$2000. Came in at the top end of that, but quality costs especially with these rifles.


I really wanted an 18” barrel, but they weren’t available at the time, and Bison offered such a deal on their 20” barrels ($225!) that I couldn’t turn it down. Beautifully custom Cerekoted black (after all, it is a black rifle) they guarantee 1MOA. The choice of handguard presented a problem. I wanted a monorail style, not quad, and it had to accommodate a clamp-on, adjustable gas block. A lot of freefloat handguards won’t accommodate a clamp-on, only those held in place by set screws. I really liked the new Midwest Industries rail and it will take a clamp-on gas block, but their new handguard only fits the newer “low profile” DPMS uppers. The fly in the ointment is my upper receiver is the older “high profile” DPMS style from SI. This really limits some of the components you can get. For those of you considering the SI receivers, specify the newer “low profile” DPMS style. You’ll have a few more choices available to you. Still, nothing wrong with the Apex handguards, so I went with that.


The weight is an issue, as I wanted to keep it down. Adding up the manufacturers’ listed weights for their products, I calculated 8.2 lbs for the finished product. That would have been acceptable, but when I actually weighed the finished rifle it came up to 9.5 lbs. That was disappointing, but it’s endurable. M1s and M14s weigh about that much. I think the manufacturers need to be more honest on their products’ weights.


Finally got it together with the help of a friend who had an AR barrel wrench. It went together easily and I took it to the range. First outing wasn’t good. The rifle acted undergassed, and accuracy got progressively worse. I took it home broke it down and found the barrel nut had come loose. We retightened, carefully reinstalled the Apex and went back to the range. This time was fantastic. 39.5 grains of TAC under a Sierra 168 BTHP easily got well under 2MOA with the iron sights. I adjusted the Syrac as per their instruction, easily done. Function was flawless. Cases are thrown out about 4 o’clock in a neat little pile. And the Griffin compensator, oh my! This thing shoots easier than a 5.56 and no one nearby even noticed the report. I can shoot this all day without a shoulder pad. The only problem I encountered was that the BCG wouldn’t lock back on either my second ACS mag, or the Pmag. This was bothersome, but after about 120 rounds everything seemed to break in. It locks back on all mags now. Future plans? Shoot it some more, try out some different handloads. The accuracy of this rifle begs for a scope to be fitted. I have a Leupold 3x9 Vari II sitting unused. Anyone have a recommendation for a quick release mount for the Picatinney rail?


This has turned out so well I’m planning a second AR308 build. SI has said they are coming out with some new models this year. I can’t wait.





Edited by mineralman55
Link to comment
Share on other sites

Wow. Sweet build. I got some SI receivers and am looking at doing a similar build. What are the specs on that barrel? (Twist, rifling, contour, materials)



1:10 twist, it weighs 2.5lbs, just looks like a standard contour. Go to the Bison Armory website and take a look. If you call Ben he may even give you the discount still.


Yah, I need to get some more pics of this. It's a good looking build.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...