Normally when I see innovations in the AR-15 market, they come in the form of a component that can be easily combined with others. Something like BCM’s KMR handguards that used a magnesium-aluminum alloy or Proof Research’s carbon-fiber-wrapped barrels. These are cool products, but they can still be used by enterprising homebuilders like yours truly. So I’m not usually impressed by a lot of the premium AR-15 builders out there, simply because I can do something similar, and I enjoy putting AR-15s together. Your mileage may vary of course. You may be happy to pay someone else for labor. However, there are some manufacturers making some innovations to Stoner’s design that are much less easily integrated into homebuilds. Something where they’re willing to push the envelope and offer something new. Let’s look at a couple.

Knight’s Armament E3 Bolt
A standard AR-15 bolt uses eight square lugs. The lugs are square because of manufacturing processes available at the time the rifle was originally designed, but any engineer will tell you that corners tend to focus stress.¹ As a result, the standard replacement interval for a bolt is 5,000 rounds (or so). Your bolt may last longer, but that’s the usual interval that the manufacturer suggests. Knights changed this by rounding all of the lugs, as seen in this picture. A standard bolt is on the left; the E3 bolt is on the right. Both have extractors removed.

Now, this has the downside of requiring a nonstandard barrel extension to work. So you’re stuck with Knights’ barrels. Not that those are bad barrels. On the other hand, the bolt life is expected to exceed that of the barrel. In Ballistics radio’s endurance test of an SR-15E3, they put 20,000 rounds through without cleaning or bolt breakage. The E3 bolt is available on all current Knights Armament rifle builds.

There are other proprietary things in the SR-15 design, like a nice ambi lower and an intermediate length (longer than midlength, shorter than rifle-length) gas system, but these can be had elsewhere, and have been done by others. The SR-15 is a pretty complete package but the coolest part is that nifty bolt.

Cobalt Kinetics C.A.R.S.
Cobalt Kinetics makes some really nice looking rifles. But lots of people have some CNC wizards to mill cool things out of billet aluminum, and if you choose handguards and receiver sets from the same manufacturer, you can get (or make) other cool looking rifles too. On some of their higher-end rifles, they have the C.A.R.S. system, which is aimed squarely at the competition shooter. When you’ve fired the last round from your magazine, the bolt locks open, just like on a regular AR-15. But the empty magazine also drops free automatically. No mag release press required. And when a fresh magazine is inserted, the bolt goes forward to chamber the next round automatically. This system can be disabled with a switch, and there are still the regular magazine catch and bolt release on the lower. This system requires some hand tuning during assembly, and is only offered on complete rifle builds. And yes, they’ll do custom colors if you like.

I love to see companies pushing the envelope and offering a product that stands out from the crowd.