Fab Defense GL-Core: Solving Milspec Vs Commercial

The GL-Core stock from Fab Defense uses a novel system of polymer inserts to change the stock between milspec and commercial diameter buffer tubes.

If you’re like me, you’ve built a few ARs. One of those was probably a budget AR, and maybe you had some parts in the bin to use up. This happens to me all the time: I’ll find a trigger assembly or a barrel or a fancy charging handle and suddenly I’m shopping for lowers.

Somewhere in the mix I hit a snag, and realize I’ve got a commercial spec buffer tube. Lord only knows why they continue to exist, but they do, and they seem to be breeding in by gear-bin.

The incompatibility between Milspec or Commercial stocks and their buffer tubes is a ridiculous lack of standardization, but it doesn’t appear to be going away any time soon.

I’ve tried a few different “swings both ways” stocks in the past, and have generally been disappointed. The fit is either ridiculously tight or rattling and loose.

That was until I started playing with the GL-Core.

The GL-Core is a new stock design from the established injection polymer molded manufacturer, which updates their AR-15 stock design to a more modern aesthetic. You’ve got a curved toe, rubberized buttpad, three sling mounting points and a pair of QD cups.

Those I think are all pretty much a requirement for a decent stock design on the modern market. Magpul has set the bar high, and any modern manufacturer looking to build these things has got to hit the major check boxes, or why would anyone bother buying?

But what sets the GL-Core apart is the insert system that allows the user to convert the stock from Milspec to Commercial diameter.

At the front of the stock, right under your cheek, are two removable tabs, left and right. With a flat nose screwdriver (or a knife tip if you’re a heathen) you can compress the tab and slide out the insert. Then grab the left and right replacement inserts that fit the actual buffer tube you’re working with, and slide them in. The whole thing takes about a minute.

Author’s shooting buddy Wally F begrudgingly tries the GL-core on a Matador Arms SKS instead of his standard issue C7.

It’s such a simple concept, I’m amazed I haven’t seen it done elsewhere before. That 2 inch segment of surface contact on either side of the tube keeps the stock freely moving, but still firm and without rattle. I don’t feel like there’s a lot new happening in the world of stocks, we’ve reached a level of refinement over the past 15 years that has pretty much peaked. But this system stood out to me as addressing a long standing irritation.

Edward O

Edward is a Canadian gun owner and target shooter with a Bachelor’s Degree in Journalism. Crawling over mountains with tactical gear is his idea of fun. He blogs at TV-Presspass and tweets @TV_PressPass.


  • Maybe it’s a Canada Thing and I just ain’t gonna know from over here on the other side of the map where our dopey gun laws are a different flavor of stupid, but it had honestly never occurred to me that Commercial buffers were still a problem anyone had in [CURRENT YEAR]. Good on Fab Defense for takin’ care of the neighbors, anyway.

    • Juggernaut

      A lot of rifles come stock (pun intended) with commercial buffer tubes

  • noob

    that’s actually a lot nicer looking than I thought a shim kit would be.

  • BS

    That stock has a perfect buttpad and MIL-SPEC and comertial capability in same stock, i like it.

  • Richard Douglas

    The Rogers Super-Stoc has been doing that for over 5 years. It is missing the derpy angled foot, is insanely light, and rock solid when locked in place. It even came stock (no pun intended) on Colt 6920s for a while. Yes, Colt stopped using it, because the early model had issues with soft plastic allowing QD swivels to pull right out, but that has long since been corrected. Invented by the same Bill Rogers that invented the Wilson 47D 1911 magazine.

  • Marcus D.

    For one, I don’t know why there are two different specs, and two, most manufacturers don’t tell you one way or the other which spec it is. That is both frustrating and needlessly expensive.

  • mazkact

    Mylar or Kadex sheet material (usually.010″ to .015″)cut to fit the full length around the buffer tube accept for the flat), superglue it in the butt stock and Viola no more rattle.