One of the few components of an AR-15 that can truly be called a work of art is the Bolt Carrier Group (BCG). A quality BCG and a beautiful thing to hold in your hand. It is a substantial piece of metal that (if made correctly) has been carefully machined from quality materials. Choosing a BCG with the latest exotic materials, high tech coatings and meticulous craftsmanship can hit your wallet where it counts. You can go the opposite route and try and spend as little as you can on a Bolt Carrier Group and wind up with inferior materials, coatings and workmanship. It is possible to get a BCG as little as $70 and as much as $350.
My individual sensibilities lie with getting as much quality where it counts as my budget will allow without overspending for a name brand, attention to details that don’t matter or unproven gimmicks. So, in applying my sensibilities to bolt carrier groups, I am always on the hunt for a quality BCG that strikes the right balance of materials, features, build quality and price. I think I may have just found the ideal combination in the St. Croix Tactical Nickel Boron Bolt Carrier Group (SCT NiB BCG).
I ordered the SCT NiB BCG directly from St. Croix Tactical’s web site. SCT offers a range of BCGs. Their least expensive is a phosphate coated BCG for $79.99 and their most expensive BCG that features a Ion coated titanium carrier and NiB coated 9310 bolt for $344.99. Keep in mind that I am looking for proven materials and coatings on a quality machined BCG. This led me to their NiB coated BCG that is selling for $99.98.
This BCG is for 5.56/.223 (which is also suitable for AAC 300BLK). The bolt is made from 9310 steel that has been shot peened and Magnetic particle inspected (MPI). The gas key has been secured with grade 8 hardened fasteners which are staked per mil-spec. The extractor uses a black extractor insert with a crane o-ring. The entire BCG is coated in Nickel Boron.
My first BCG was a WMD NiBx BCG that I purchased for $150. I have been very happy with the WMD BCG. I also have a Palmetto State Armory Premium BCG that is parkerized. Both are quality BCGs. I would probably have purchased another WMD, but I saw the deal on the SCT and the positive reviews. I love finding a god deal on quality parts, so I had to check it out.
I ordered directly from St. Croix Tactical’s web site for $99.98 with free shipping. The BCG arrived in under a week and I have to say I am very pleasantly surprised.
The NiB coating appears to be even and looks to bea nice Satin Grey. This looks more evenly applied then the NiBx treatment on the WMD BCG. I believe the NiBx treatment on the WMD is slightly harder then the NiB treatment on the SCT BCG. Nickel Boron and Nickel teflon treatments tend to achieve a rockwell hardness of 49-52. Magnesium phosphate is usually around 30 on the Rockwell scale. NiBx is 70-72 and Fail Zero’s Nickel Boron process is 82-85.
(Left to right: PSA Premium BCG, WMD NiBX BCG, SCT NiB BCG)
On first inspection, the machining on the SCT BCG is impressive. The exterior surfaces are all cleanly machined with no tooling marks. Upon closer inspection, there are some minor tooling marks on the inside of the BCG. I found tooling marks in the channel for the cam pin (picture 1); on the inside of the carrier on either side of where the hammer falls on the back of the firing pin (picture 2); On the inside of the very back of the carrier (where the carrier engages the buffer)(picture 4); inside the carrier just under the rear fastener (picture 5); on the carrier, just behind and below the gas key (picture 6); and in the hole that holds the cotter pin (picture 7). Of all these parts of the carrier that show tooling marks, the only spot that could possibly affect the operation or performance of the BCG would be (picture 1) in the channel for the cam pin. The cam pin rides in it’s channel to transfers some of the rearward kinetic energy, from the gasses returning from the barrel, into rotational force to unlock the bolt lugs from the barrel extension. The tooling marks may eventually cause wear on the cam pin and cause some issues with disengaging the bolt lugs. We will have to keep an eye on this part and follow up with a report after a few hundred and then a few thousand rounds. The rest of the tooling marks are in locations that do not engage any moving parts. It appears to me that SCT has put the time in to do an excellent job machining the vital parts of this BCG and have left minor tooling marks where it doesn’t matter. A case of putting your time and money into what matters and not being pragmatic about the rest. If I wanted a flawless piece of machining for my AR15 that is going to be a safe queen, I would go out and buy a flawless BCG for $350. That’s not what I am going for here. I want a quality BCG that is reliable, does the job, is easy to clean so I can keep it running.
(Minor tooling marks on inside surfaces)
This is a very minor nit pick of an otherwise excellent part. Bonus points to St. Croix Tactical for including a full auto profile bolt carrier instead of the lighter semi-auto profile bolt carrier. While the bolt is not marked with the MPI engraving, the web site claims that the bolt is in fact MPI tested.
People make a big deal over the staking of the gas key on the BCG. This is a big deal because this is the major point at which the genetic energy of the gas system is transferred to the BCG and cycles the weapon. The staking of the fasteners that keep the gas key firmly attached to the bolt carrier has to withstand high heat, vibration and strain. If the fasteners are not properly staked, they can work themselves loose and the gas key can develop slop in it’s interface with the bolt carrier. If this is to happen, it can cause a failure to cycle or even a failure to return to battery. While the SCT BCG is properly staked and I don’t have any immediate concerns about the gas key working loose, I would have liked to see the staking be a little more pronounced. Specifically, I don’t think the staking has engaged the fasteners aggressively enough. This is right on the line between good enough and almost not enough. Again, I am being picky. Most people would see that this is staked and the staking does engage the fasteners and call it a day. Take a look at the pictures and decide for yourself. Let me know what you think. Am I being too picky? Is there such a thing as too picky?
The bolt is made of 9310 steel. This is claimed to be better then 8620 steel or Carpenter 158 steel. SCT doesn’t list what the carrier is made of. The bolt is shot peened to increase the hardness of the bolt. They use Grade 8 fasteners, which is the industry standard. The entire BCG is coated with a very even treatment of Nickel Boron (NiB). This process isn’t a coating, but a treatment of the surface layer of the steel to harden the steel. This has three main advantages over the standard phosphate coating. It protects against corrosion, reduces wear and provides increased lubricity. Ultimately, the NiB coating allows easier cleaning of carbon from the BCG and makes it easier to keep the BCG lubricated. The Crane o-ring seems to be the premium o-rings and they even included the black extractor insert. Overall, the material selection is top of the line without going into exotic materials like Titanium.
This is a high quality BCG that is being sold at an amazing price. This BCG has the materials selection, build quality and coating of a top tier BCG. If this BCG had a name brand like Spikes, BCM, or Wilson Combat, it would easily fetch a price tag of $200 or more (plus shipping). I’m about paying for quality and not for a name. St. Croix Tactical has made a BCG that balances top notch materials and quality where it counts to deliver a very high value Bolt Carrier Group. If you are looking for a high quality BCG and you don’t mind knowing there are some minor tool marks, you should definitely make an SCT NiB BCG part of your next AR build!