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First Look – SI Defense .308 Ambi Rifle Build

Posted on February 17th, 2015 by ar15news

Over the past few months we’ve had the opportunity to work with the guys from SI-Defense in helping spread the word about their new products including their new .308 billet receiver set that features “mirrored ambi controls”. Remember that term as you’ll see what we mean soon. Now that the .308 Ambi receiver sets are hot off the machines, SI-Defense asked if we would want to build our own rifle using these receivers…and of course we’re not gonna turn that down. ūüôā So this is the start to our multipart article showing the rifle we built, what parts we used and then we’ll do additional articles once we’ve actually had some time to shoot it for a while.

The first thing that arrived were the SI-Defense .308 Ambi billet receivers. The mirrored ambi controls on the receivers are pretty mind blowing. When you push on the Bolt Catch, Bolt Release or Mag Release on one side the same button on the other side moves as well. It really is pretty amazing that the ambi controls are mirrored and not just an added lever that is completely different than the control on the right side. The dust cover is pretty cool too in that it is easy to remove/install even with the handguard installed because it snaps into place.

SI-Defense 308 Ambi Rifle 1

A few months ago Rainier Arms introduced their new .308 UltraMatch BCG. Once I knew this build was going down I promptly went on the Rainier Arms website and purchased one. The finish on this thing is a really nice deep Black Nitride that is super smooth. The angled cuts toward the front and fluting at the rear of the carrier look pretty sweet.

SI-Defense 308 Ambi Rifle 1

If you’re gonna build a gun you definitely need a barrel, right?! Right. I’ve posted about AERO Precision barrels many many times before whenever they have a new model to introduce or a special deal etc. but have never personally used one myself. So for this build I contacted my buddy Chad over at AERO Precision to see if I¬†could¬†get my hands on one of their 16″ Mid Length .308 barrels. They are made of 416 Stainless Steel and I’m really excited to see how well they perform. You might be thinking “A 16 inch .308 build? Most guys do 18¬†inches or more.” and you’re right but I just built an 18″ like everyone else and¬†wanted do something a bit different. Because I know big bore rifles can be a bit¬†ornery I installed a SLR Rifleworks Sentry Adjustable Low Profile Gas Block along¬†with¬†the Rainier Arms Nitride Mid Length gas tube.

SI-Defense 308 Ambi Rifle 1

Along¬†with the SLR Rifleworks Sentry Adjustable Gas Block, I also used the SLR Rifleworks SOLO 15″ KeyMod handguard, Hand Stop and their Synergy BCF muzzle device. It truly makes for one killer looking setup and can’t wait to see how well it performs.

SI-Defense 308 Ambi Rifle 10

SI-Defense 308 Ambi Rifle 1

Along with making some pretty amazing ambi receivers, SI-Defense also makes a mean looking ambi charging handle called the MACH10 which stands for Modular Ambi Charging Handle for AR10. This specific one has a neat feature where it latches on the inside of the receiver but they will also offer an outside latching MACH10 and a MACH15 charging handle as well.

SI-Defense 308 Ambi Rifle 1

As with all of my builds this one¬†includes a Battle Arms Development Ambi Safety. I don’t own a single AR that does not have one and no I don’t get them for free. Its one of those products that I have honestly grown to love and buy them for every build. ¬†

SI-Defense 308 Ambi Rifle 1

Along with upgrading the Safety I also upgraded the Trigger. I usually use either a Geissele or CMC Trigger and decided to try the Geissele S3G trigger in this build. The S3G is not really designed for a rifle with higher recoil as it has a very light trigger pull and could bump-fire easily so I used the heavier spring that comes with it. This is kind of a trial run and will be interesting to see how it performs in a .308.

SI-Defense 308 Ambi Rifle 1 SI-Defense 308 Ambi Rifle 1

Oooohhhh. Look at that sexy beast!! I also added a Trijicon VCOG, Magpul MBUS PRO sights, UBR stock and a MOE+ grip to finish off the build. I think it turned out to be an one of the best looking rifles I’ve built.¬†

SI-Defense 308 Ambi Rifle 1

These pics are hot off the press as I just finished this build over the¬†weekend. This week will be its maiden voyage to see how well she runs and get the gas system all dialed in. Will update you with an additional article detailing its performance at the range and hopefully some 100 yard groups. If we don’t get accuracy data on the .308 AERO¬†Precision barrel for that article it will be in an additional one for sure. Below is a list of links for the parts we used in this build.

AERO Precision
Battle Arms Development
Rainier Arms
SLR Rifleworks

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