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TripleBravo
14 July 2012, 21:08
In 2012, Seekins Precision brought two unique new rail designs for the AR to market. The first caters to a community of AR shooters Glen Seekins is passionate about – the “three gunners.” Our own zero7one showed us the triangular SP3R here: http://www.weaponevolution.com/forum/showthread.php?3916-Seekins-Precision-iMRT-Billet-Upper-amp-3-Gun-Rail

Recently, I was given the opportunity to build an upper assembly with the second new rail design – the Modular Combat/Competition Suppressor Rail, or MCSR – by pairing it with the Seekins Precision iMRT-R. The billet iMRT-R receiver is designed to work with the MCSR for a superbly rigid rail/receiver interface. What follows is a photo essay of how the build went together.

The MCSR comes shipped with everything you need to mount it to a standard upper receiver.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/SP-MCSR01-onwhite01-crop1500-B3.jpg

When used with a standard upper receiver, the MCSR attaches to the same aluminum barrel nut used with the Seekins BAR quad rail. While this nut is proprietary, it can be mounted with a standard AR barrel nut wrench.

The iMRT-R ships with a titanium barrel nut.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/SP-iRMT-R-right01-onwhite01-crop1500-B3.jpg

The iMRT-R is a solid piece machined from billet aluminum, so the MCSR actually mounts directly to the upper receiver rather than the barrel nut.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/iMRT-MCSR-together01-onwhite-crop1500-B3.jpg


The iMRT-R barrel nut, like the first generation of Seekins SAR quad rails is attached using a 1 and 1/8 inch wrench.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/SnapOn-1-1-8-crop1500-B3.jpg

I used a crow’s foot wrench so that I could then use my torque wrench to tighten the barrel nut to 50 foot lbs.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/50FtLbs01-crop1500-B3.jpg

For this build, I had an opportunity to use Seekins new adjustable low profile gas block.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/SP-AdjustableGB01-onwhite01-crop1500-B3.jpg

I used it because I decided to make this build “all Seekins”, but the adjustable gas block is much more suited for an upper that’s likely to see suppressor use. Since this one is not, I decided to skip my usual practice of pinning the gas block in place – in case I decide to swap it out and use it for it’s intended purpose.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/SP-GBmounted01-crop1500-B3.jpg

While its up to the end user whether or not to utilize the top rail, it’s a decision best made prior to mounting the MCSR to the iMRT-R. Once mounted, the top rail cannot be removed or installed without removing the MCSR from the iMRT-R. Installation of the top rail is simple enough though.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/TopRailFit01-crop1500-B3.jpg

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/TopRail-Tighten01-crop1500-B3.jpg
(Once the top rail is in place you must tighten the screws by using a torx driver through the bottom of the MCSR.)


The MCSR has two anti-rotational tabs that run along the side of the upper receiver. It’s then secured to the iMRT-R (or the barrel nut when used with a standard receiver) with eight screws. When they are all tightened, the MCSR is rock solid.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/AntiRotationTabs01-crop1500-B3.jpg

The accessory rails can be added or removed once the MCSR is installed. They can also be mounted in the angled slots that run between the three, six, and nine o’clock positions. Note that the attachment screw is recessed so that it does not prevent a rail slot from being used.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/Rail-top01-crop1500-B3.jpg
(Top of accessory rail.)

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/Rail-Back01-crop1500-B3.jpg
(Underside of accessory rail.)


I chose to use only one along the bottom so that I could mount a Gear Sector hand stop to the MCSR.

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/SP-MCSR01-crop1500-02-B3.jpg

There ya have it…one awesomely rigid tubular upper assembly!

http://i718.photobucket.com/albums/ww189/wjt1169/Seekins%20Precision%20MCSR%20and%20iMRT-R/Holding-SeekinsMCSRbuild01-crop1500-B3.jpg

As its name implies, the MCSR design works equally well over a short barrel with a suppressor attached. I hope to bring you more details on that in the near future, so stay tuned!

In the mean time check out all the great stuff available from Seekins Precision here:
www.seekinsprecision.com (http://www.seekinsprecision.com)

Ask any questions or discuss in this thread: http://www.weaponevolution.com/forum/showthread.php?4033-Seekins-Precision-MCSR-amp-iMRT-R-Discussion.&p=36978#post36978