Beautiful, rigid, strong, customizable, easy to install and a well thought out design are just some of the adjectives that come to mind when I think of the Geissele SMR (Super Modular Rail) Mk3 that I installed on my newest AR-15 build.

Several months ago, when I was deciding what my newest man-Barbie would be wearing, I was browsing various forums for ideas and came across a particular photo that ended up being the inspiration for my entire AR-15 build. After contacting the photographer and discovering that his AR-15 was sporting a Geissele rail, my research began.

I had already made the decision that I didn’t want my AR-15 to have a free floating handguard that everyone else had. I wanted it to have integrated QD mounts, to be modular and allow me to choose where to put picatinny rail sections, not overly difficult to install and most of all, strong. I was happy to find all of these features with the Geissele SMR Mk3.

Features

I suppose it may be odd to some that upon receiving it, one of the features that excited me the most about the SMR Mk3 was the barrel nut (weird, right?). Unlike all of the others I have installed, the Geissele barrel nut does not need to be indexed or timed for proper gas tube alignment or alignment to the upper receiver. Insert the barrel into the upper, grease the threads, use the included barrel nut wrench–which includes a bottle opener, by the way–to torque the nut to a value of 40ft/lbs and the barrel is installed. It is that easy.

Specifically, almost every feature that I like about this rail has to do with the way the barrel nut was designed. I will break it down for you:

Easy installation and removal of the rail: There are two milled channels around the entire circumference of the barrel nut. After the barrel and barrel nut are installed, the Mk3 rail is then slid over the barrel nut and leveled (I clamped a rear sight onto both my upper receiver and the rail to align them). There are two bolts that pass through the rail, along the channels and then screw into the other side of the rail. These bolts are to be torqued to no more than 5ft/lbs.

Lastly, gently tightening the two rubber tipped set screws on each side of the rail to come in contact with the upper receiver completes the installation. To remove the rail, just do everything I just listed in reverse order. Take a look at the video above to see me demonstrate this process.

Rigid and strong: The Mk3 is rigid and strong due to the length of the barrel nut. Because the barrel nut is longer, it supports more of the handguard from the inside, once the handguard is slid over it. Geissele left little-to-no wiggle room with this element. The fit between the outer diameter of the barrel nut and the inner diameter of the rail is almost perfect.

To better describe how the length of the barrel nut can affect the overall strength of the Geissele SMR, imagine this scenario: hold out your arm and pretend you are sticking only your closed fist inside of a large hollow pipe. With your arm extended and only your fist supporting the pipe, lift the pipe off of the ground. Now, this time, think of doing the same thing again, only instead of using your fist, using your entire forearm inside the pipe. It makes sense that the latter method is the easier. The same concept applies to the fit of the barrel nut within the handguard.

Anti-rotation and movement: Arguably, this could fall into the “rigid and strong” category, but I feel that it is significant enough to discuss separately. I know that a weakness of free floating forends is the possibility of rotation and forward movement. Once again, the barrel nut plays a major role with aiding and almost completely removing the possibility of any movement of the Geissele SMR rail.

Because the rail is installed with the cross bolts as described above, I see no plausible way for the rail to move forward unless the bolts are removed completely.

With the two set screws making contact with each side of the upper receiver and the cross bolts installed straight through the rail and barrel nut, it would take a tremendous amount of torque to get the rail to twist. When I held my AR-15 after installing the Mk3, I thought “this thing isn’t going anywhere.”

Modular customization: This is one feature of the Mk3 that does not rely on the barrel nut. Modular rails are nothing new on the market, but, it has been my experience that Geissele has one of the sturdiest modular systems available.

My Mk3 came with three modular picatinny rail sections and three corresponding attachment pieces–two short and one long. What stood out to me the most when looking at the sections (using my Wilson Combat TRIM rail on another AR-15 build of mine as a comparison) was the way they fit into the rail.

Each modular picatinny section had raised circles on the back that matched up with the cutouts on the rail, which prohibited me from being able to twist the section when setting it in place–once again, strong and rigid.

There are a number of different locations to place rail sections, so the configuration is entirely up to the user, which makes the Mk3 quite customizable. So far, I have attached a Magpul AFG on the bottom of the rail, using the long rail section, and I have not experienced any issues with it coming loose or moving on me.

Final Thoughts

I experienced only one hiccup during my installation process of my Geissele Mk3. Turns out, it was a case of “operator error.” My Mk3 rail did not initially fit my upper receiver because my AR-15 upper receiver was a billet receiver.

Geissele designed these rails to fit typical mil-spec forged receivers and even mentions on their website that a billet upper receiver may not be compatible (way to miss that, Nate). This was quickly resolved by Geissele when they offered to try and machine my rail to fit my upper receiver it if I were to send it to them. Talk about great customer service, no?

With a Geissele SMR Mk3 coming in at around $300, price may be an issue for some. However, it is of my opinion that it is an appropriate price with all the above features considered. If you are in the market for a rail for a new build or looking to upgrade from your existing one, then you may want to consider taking a look at what Geissele has to offer.

Featured image courtesy of Geissele.com