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.