When we last told you about the SureFire Advanced Rifle Operating Core and Optimized Bolt Carrier we weren’t sure when it would be available commercially. But SureFire had the OBC on display at SHOT Show and told us the first run are just finishing up production.
While the entire AROC consists of an enhanced Bolt Carrier Group, Barrel Extension, Buffer and Spring, the OBC is a drop-in Bolt Carrier Group which fits both piston and DI ARs.
The OBC features an internal weight which is spring loaded in both directions. This, along with the other elements, combine to offer additional travel time. 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 the OBC, it’s 38 milliseconds. That slight difference is signifigant, especially when firing full auto or suppressed, or both. You’ll also notice that the gas key has a single screw. It comes with a 2 oz H2S buffer and an included Action Spring offers additional tension.
Tags: Surefire
How comes this is not plagued by the exact same issue that affected Colt 9mm BCG, namely that it was reciprocating too far backward, which allowed it to gather up a whole head of steam and break the bolt catch on its return stroke? Colt eventually added a spacer to remove the excess travel.
I can’t really answer your question well enough but I can point you to the previous article which might be helpful. I think I understand the mechanism but not well enough to explain it.
https://ssdaily.tempurl.host/2017/09/20/mdm-17-surefire-advanced-rifle-operating-core/
That should have been in reply to Aono, sorry bout that!
I get how it works; they shaved off the rear carrier key bolt and shortened the buffer to allow the carrier to travel an extra ~1/4″ back into the buffer tube. The problem with that is that’s exactly how Colt designed its 9mm, then realized they would need to add length back to the buffer to PREVENT it from reciprocating too far back. The reason being that on the last round bolt hold open the carrier is slamming forward into the catch. If it slams too hard it will break. I can’t see how this doesn’t introduce exactly the same issue.
The 9mm guns typically have a much stronger return spring because they are direct blowback so the weight of the bolt and the spring is the only thing keeping the bolt closed long enough for pressure to drop. Hopefully surefire had the foresight to test their product against the failure that colt experienced with their longer stroke 9mm guns.
The SF BCG does include a longer spring but no word on its rate. I suspect it’s similar to the A5 in that regard, not “extra power” just longer. So that’s probably a good sign. Still, color me skeptical, even though I really want to like the idea of extra Sullivan goodness.
BCG has an internal counter weight which combats the problems you are describing.
I had considered that after I posted as well. The weight should lessen the initial blow and distribute it better then the entire weight of the carrier coming to an abrupt halt.
It’s Stoners design.
https://www.youtube.com/watch?v=gOUKXIrDE0I
***
-Stoner
+Sullivan
Looks like they’ve addressed the exposed extractor pin.
If the price is decent I’d try it out. An over gassed gun is a butt to deal with and if this helps it’s another option in the toolbox.