B5 Systems

MDM 17 – SureFire Advanced Rifle Operating Core

SureFire’s new Advanced Rifle Operating Core is a system consisting of an enhanced Bolt Carrier Group, Barrel Extension, Buffer and Spring.

Because AROC requires a new Barrel Extension, they’ve also developed a Drop-In BCG called the Optimized Bolt Carrier. It includes Buffer and Spring. Although it’s not fully optimized like AROC, it is backward compatible with existing Mil-Spec AR pattern rifles.

Below, you can see (top to bottom) the AROC, OBC and standard AR BCGs.

The AROC Bolt offers 30% longer bolt lugs. Naturally, this means it requires a longer Barrel Extension. This was done to eliminate bolt lug breakage.

Additionally, the Buffer is longer than the Mil-Spec version. The H8S comes with AROC and is 8 oz. The 2 oz H2S comes with the OBC. The included Action Spring offers additional tension.

Regardless of which SureFire BCG, the Gas Key features a single screw which SureFire’s Barry Dueck related is stronger than the standard two screw model.

The BCG features an internal weight which is spring loaded in both directions. This, along with the other elements, combine to offer additional travel time. This also affects the angle from the bolt to the feed ramp. With a standard M4, the angle is 52 Deg. For an M16A4, it’s 45 Deg. But with AROC, it’s 37 Deg.

When the Bolt is at the end of its stroke while using a Mil-Spec BCG, it takes 28 milliseconds for the bolt to travel back into battery. With AROC, it’s 38 milliseconds. That slight difference is signifigant, especially when firing full auto or suppressed, or both.

On the range, AROC was demonstrated successfully with both Piston and Direct Impingement rifles. Although we previewed a version of this at 2016 SOFIC, SureFire has been working with suppliers to bring the cost down signifigantly from the initial estimates. At this point, Bolt Carrier Groups are a commodity item. Prices are so low that even specialized versions, such as this, have to be price competitive as possible.

No word yet in when this will be released commercially.



19 Responses to “MDM 17 – SureFire Advanced Rifle Operating Core”

  1. Joglee says:

    Few issues.

    First is changing a barrel extension is hard, like really hard. Especially considering gas port timing is done after a barrel extension is installed. Taking one off and getting it to properly time with a pre existing gas port will be hard.

    Second unless there is a spring or they staked that extractor pin in, that’s going to fall out with recoil.

    There’s a reason the extractor pin doesn’t extend past the bottom carrier, and why LMT extended the lip of that section of the carrier. Also why the KAC E3 bolt has a spring to retain the pin.

    Lastly why go from two bolts securing the gas key to one? Those bolts are the most common failure on a bolt carrier.(not saying it’s common, but the bolts holding the key will fail before any other Bolt carrier part.)

    • Alex says:

      I reckon that’s why SF came out with both options. A Drop-in upgrade in the shape of the OBC as opposed to the AROC which is an almost complete redesign akin to what KAC did with their e3 bolt.

      Also, context. This is presented at an industry show, so I’m going to venture that commercial consumers aren’t the primary target market for the AROC.

    • Jordan Bowles says:

      Generally one big bolt is better than 2 smaller ones, it does seem like it might be a bigger screw. It also looks like the key might be contained by 3 sided pocket rather than the normal slot, allowing the bolt carrier to directly absorb any rearward force on the key instead of that force going threw the key screws first, I suspect aside for loose and over tightened screws that’s what breaks them.

    • Rob says:

      They use one bolt on the carrier key so that they could shorten the back end of the key. This, along with the shorter buffer allows for a longer stroke. This allows for a slower cyclic rate and gives the magazine more time to properly present a round.

  2. jbgleason says:

    I ho-hum lot of “improvements” I see offered because they are designed to “fix” something that isn’t a real problem. But in this case I am interested. Sheared bolt lugs are absolutely something I have encountered multiple times with high round count weapons. Now what I really want to see is some testing data convincingly showing a longer product life.

    Then show me data that says the juice is worth the squeeze. BCG’s (good ones) are readily available for under $100 right now. That means this can’t be $300 for 20% more product life.

    • d says:

      I agree, but is it just product life we’re getting out of these, or is there something else going on?

      • straps says:

        The poster you replied to said that bolt carriers are cheap and easily replaced when keys or lugs fail. Which us fine if you shoot paper. Not so much if you shoot movers that shoot back. So there’s that.

        These improvements are designed to address malfunctions and failures exacerbated by shortening barrels and affixing suppressors to them while firing modern ammunition at full-auto through a 60-year-old mechanism.

  3. EzGoingKev says:

    OMG I cannot wait until they melt down over at M4carbine.net over the staking job.

    As far as bolt lugs go, KAC’s rounded and radiused lugs are the way to go.

  4. Paul says:

    This was designed by James Sullivan at Armswest, designer of the Surefire 60 & 100 round mags, but probably more well known for scaling down the AR10 to the AR15. He probably knows the intricacies of the platform.

    • justacivilian says:

      If that’s true I wonder if there’s any chance of seeing a surefire rifle one day.

  5. Jamie Wiedeman says:

    Thanks Eric for the coverage of the AROC and OBC on SSD.

    The AROC is more of a complete upper parts and barrel replacement.

    The Optimized Bolt Carrier (OBC) is a drop in operating system for the M4 and MK18 with a complete bolt carrier group, buffer, and recoil spring. These kits will be a nice upgrade for any AR15, especially effective on short barrel rifles, or over gassed weapons.

    • d says:

      What are the chances of seeing the OBC in Mk18s in the next few years? I could see it as part of an updated suppressor kit.

  6. Nick M says:

    Holy cow, I need sleep. I thought I read receiver extension (buffer tube). Notbarrel extension. Yikes.

  7. SGT Rock says:

    Everybody is ignoring the huge elephant in the room… wherein the problem lies with the buffer and spring.

    That damn thing has one of the worst characteristics upon return to battery/firing w/wobble and friction. What can be done?

    How about implementing a captive buffer spring? Not only would it help mitigate recoil, but also help w/feed and cycling issues.

    • James says:

      There is a captive spring system out there already. The Silent Spring System from JP Enterprises.

      • AlexC says:

        Could you use the JP Enterprises spring with the surefire OBC?

        • Rob says:

          The 308 silent capture spring might have the correct stroke length. I have never tested the silent capture springs myself so I cant say how well they work.