This is weight savings the hard way, considering that most of what’s cut away is 7075 or 6061 aluminum. You just can’t save that much weight that way.
There are FALs kicking around Latin America and Africa with a big borehole like that in the magazine well — that’s because they were supplied clandestinely by Cuba, and los Pollos Cubanos used the boring bar (or maybe a fly cutter, we defer to the machinists in the audience) to remove the Batistiano Cuban crest in hopes of concealing the guns’ origin. (Lotsa luck. Western intel agencies had the manifests of the deliveries, by serial number).
Aero Precision has gotten into the game with some gimmicky skeletonized lowers. This is not a production item, but was an experiment:
That’s also thanks to TFB. Structurally, it might hold up or it might not (really, most of the material in the sides of the lower is there to provide dust seal, and, to a limited extent, a shear web, so there’s no reason skeletonizing shouldn’t work, structurally). But the total weight savings is nominal: 0.169 lb or about 2.7 ounces. (About 0.08 Kg for those of you who roll that way). They could probably have saved almost as much by milling off the A2 reinforcements to the pivot pin lugs and buffer tower areas.
That gives you an idea of what Bubba’s Boring Bar Blaster actually saved: less than 2.7 oz, to be sure. That’s winning the game the hard way.
Aero Precision is not alone. Daytona Defense & Tactical sells a skeletonized “Reaper” lower for $85 bare and $90 anodized black. It looks like they took many of the same cuts Aero Precision did (we’re not going to guess who was first).
So what’s the game? As you might guess from all the discussion of weight, The Lightest AR Going. There’s a Tumblr where a guy aimed for 60 ounces (he overshot but not by much), and there are several other competitors around. So a new guy’s aiming below 60 ounces. Of course, his definition of a “fully-functional AR” may not gibe with yours — one of the first parts he sacrificed was the bolt catch, shortly followed by the magazine catch (he’s making a fixed-mag 10-round firearm). And we’ve got our doubts about the long-term viability of his aluminum bolt carrier (yes, really). But even he has said, he’s not drilling the thing full of holes.
It might be that X Products got the whole Gun of Skeletor thing started by, after a skeletonized drum magazine caught the public’s eye at SHOT, making a run of the things. (Not a short run, either. For 2015 they made 1200 Skeletonized mags for SR-25 pattern .308s, and sold ’em out). The silhouette of the skeletonized AR-15 drum has been used as a sort of trademark by the company ever since.
Hey, you want a light AR? Going to shoot it with irons? Get an old Colt SP1carbine. Yes, it will have some compromises: iron sights only, of the less precise (and slightly harder to adjust) A1 flavor. No rails or freefloated goodies. But it’s only 6 pounds and change. If you want to get to 4 pounds and below, you can only do it by accepting unpleasant recoil, shorter life, and compromised performance.
If that’s a good deal to you, or if you just want to experiment, have at it.