Does your battle rifle rattle? No I don’t mean in a good way, but the bad way with wiggle room and play between the receivers. X-Shim is designed to snug everything up again for peak performance.
Some shooters say a little play between the upper and lower doesn’t matter, some say it can make a huge difference in accuracy. I haven’t experimented with it scientifically enough to know for certain, but I’d lean towards the side that it does make a difference. In precision shooting every slight movement makes a difference, and wobble in the rifle’s fit will definitely degrade consistency.
The X-Shim is designed to be an inexpensive way to eliminate unwanted play in your rifle. It’s simply 4 tiny sheets of thin plastic material that fit around your front and rear lugs on your rifle. The shims will snug up the receivers and remove most of that play.
I use a few lowers for several uppers so I definitely run across some play in my rifles at times. The X-Shim proved easy enough to install, especially with the help of the included gauges. You first fit the rear shim, then the front. The instructions tell you to make sure you can still take out your takedown pins with your fingers but I did play around with mine to see how tight I could get it. When I could still take the pins out with my fingers I still had a slight bit of play in the rifle, but it was reduced. To get all the play out I stacked a .002” on top of the .005” shim but it was difficult and required a plastic punch to remove the takedown pin so I won’t be keeping it that thick.
I can’t honestly say it improves accuracy because I feel that would take several hundred rounds in a scientific test procedure. However I will tell you I shot the best group ever out of my LaRue OBR 7.62 with the shim installed. For $12.99 I don’t see why anyone who works with AR15s wouldn’t have a set on hand for a rifle with a little wobble between the receivers. You can find them here: http://varmintlight.com/x-shim-ar-15-m16/
Story by Dustin Ellermann