While the BATFE figures out new ways to infringe upon our fun, the RECOIL team was having an idle discussion about their continued flip-flopping on pistol braces. Yours truly quipped that, if braces do ever go the way of the bumpstock, pinned and welded AR builds will get popular pretty quick in the spirit of maintaining the shortest, handiest barrel possible while still meeting the 16.1-inch minimum for non-NFA rifles.
Aside from the trending retro style of pinning an extended XM177-style flash hider on an 11.5-inch barrel, the 13.7-inch barrel provides a good answer to keeping total “barrel length” within required parameters while still ending up with a rifle that handles more like a 12.5-inch gun than a 16-inch one.
Regardless of what happens to braces, if anything, the 13.7 class of AR has held a cult following for nearly a decade and is seeming to gain steady ground as more manufacturers dip their toes into this unique configuration. At the risk of getting too meta, there’s a splinter faction within the 13.7 subculture for 13.9-inch barrels as well. Adding two tenths of an inch lets home-builders squeeze a couple more muzzle devices into the “just long enough” category but adds no ballistic or mechanical benefit that we’re aware of.
ORIGINS
As best we can tell, the commercial market genesis of the 13.7 AR came about with Noveske’s Infidel rifle — the first rifle we know of offered in this length. So we reached out to them directly to ask for some background. As they tell it, John Noveske filed the patent for the original KX-3 flash hider in September of 2006. Once they had this, he did a little bit of backward math to figure out how short he could make a rifle with this muzzle device permanently attached. When accounting for the permanent length (minus the removable cone) of the KX-3 and the back-threading to attach it, the result was 13.7 inches — producing a barrel totaling 16.2
