Para Bellum Arms Enhanced AR-15 Bolt Carrier Groups
Manganese Phosphate
While our Enhanced Mil-Spec BCG shares the same finishes as a Mil-Spec BCG, it is so much more. Enhancements include:
- Michiguns O.C.K.S.
- Sprinco Gas Rings
- Sprinco Ejector Spring
- Sprinco 5-coil Extractor Spring
- Sprinco Viton O-ring
Hard Chrome
Our Enhanced Chrome BCG shares the same core features as the base model, but with an upgrade to a hard chrome finish for the bolt head, bolt carrier, and cam pin. This finish offers improved durability and lubricity.
Diamond-Like Carbon
Our Enhanced DLC BCG shares the same core features as the base model, but with an upgrade to a diamond-like carbon finish for the bolt head, bolt carrier, gas key, and cam pin. This finish offers ultimate durability and lubricity.
Meet the PBA Enhanced BCG Family
The bolt carrier group is the heart of the AR weapon system. Arguably, it is the most important moving part of the gun. Because of this, we spent a little extra time and effort searching for the right BCGs for our guns.
Our Enhanced AR-15 BCGs are purpose built from the ground up to ensure absolute reliability and top-level performance. The story of how we got there is one of stubborn determination and uncompromising expectations. And it almost didn’t happen (several times). In the end, we are very please with how it turned out.
We like to know everything about everything in our guns. We are weird like that.
We want you to know everything about everything in our guns. We are transparent like that.
For our BCGs, we wanted to make sure that every part was fit for purpose. Each sub-component experiences different conditions/stresses and not every material or finish is best for every condition/stress. So, we agonized over the materials and finishes for each sub-component. Where there were differences of opinion, we went to the industry experts for their take.
Below, you will find the final specs of each sub-component in our BCGs. Below that, you will find some of the highlights of our BCGs. If you still have questions about our BCGs, just ask.
We Inspect/Gauge the Crap Out of Every BCG
The BCG is such an important part of the AR platform. Proper function, efficiency, and safety rely on dimensional tolerances (check out our Gas System Deep Dive series in Para Bellum University for more information). Accordingly, we gauge and inspect every single sub-component of the BCG when it arrives to us. In fact, the BCG accounts for half (41) of the 82 points of inspection and gauging on a full firearm (39 points for incoming inventory and 2 points at final receiver assembly). Visit our Quality Promise page for our inspection specifications. We are not aware of any other manufacturer who goes through this effort for every BCG.
Every BCG Test Fired
We have a lot of faith in our BCGs, before they even end up in a gun. Microbest, Sprinco, and Michiguns make phenomenal quality components. We gauge critical components when they arrive. And everything is assembled properly. However, we like to have the highest degree of confidence in our products. So, we live fire test every single BCG. We will never ship a product that doesn’t work, because every single product needs to work before we ship it.
Please note this means that every BCG could show corresponding signs of use. Rest assured: if it is sealed in the package, it has only been fired by Microbest (for HPT) and Para Bellum Arms (for BCG and Upper Receiver Assembly QC, as applicable).
Permatex Aviation Gasket
Microbest manufactures to phenomenal tolerances, to the point that their BCGs don’t actually need gas key sealant. We still have them use Permatex to seal the gas key to the carrier. It is the Mil-Spec and it provides an added level of assurance that your gas system is sealed and efficient. It is worth noting that most consumer manufacturers don’t seal their gas keys.
Michiguns O.C.K.S.
Gas key screws have a very important job and are subject to extreme stresses. While grade 8 gas key screws are good enough for the Military, we went out of our way to use Michiguns’ Optimized Carrier Key Screws (O.C.K.S.) in all of our builds. The full height knurling and crown notches deliver bombproof security of the gas key when properly staked, as of course ours are.
Sprinco Springs
Standard extractor and ejector springs are fine. But they are not good enough for us. We put Sprinco 5-coil extractor springs and Sprinco ejector springs in all of our builds for ultimate reliability. Sprinco chrome silicon spring wire is heat treated (for strength), stress relieved (for reliability), cryogenically processed post-winding (for longevity), and impregnated with a micronized molybdenum disulfide compound (for lubricity). That may seem like a lot of effort for a tiny spring, but the result is a more consistent, more reliable, and longer-lasting spring and bolt assembly.
We also pair the Sprinco 5-coil ejector springs with Sprinco CRANE Viton O-rings, because that is what the experts at Sprinco have advised us to do. Per their guidance, while you should use both the O-ring and the insert for a standard extractor spring, you want either the O-ring or the insert with the 5-coil springs (you can use both, but installation would be a bitch). Most other companies pair the 5-coil extractor spring with the insert, instead of the O-ring. We asked Sprinco for their advice, instead of blindly following the trend. The advice we received was observational, based on real life experience with the 5-coil spring, and was contrary to common practice: Sprinco advised us that, while the O-ring will have the same effect as the insert on function of the extractor spring, the O-ring/5-coil combination will far outlive the insert/5-coil combination (they have documented evidence of several hundred thousand rounds through an O-ring/5-coil combination without signs of wear or degradation).
Note that while the 5-coil extractor springs will work extra hard to tear a stubborn spent case out of the chamber, they may not be kind to your brass. If you reload, this may be a problem for you. That is why we include a standard 4-coil extractor spring and the recommended extractor insert with each BCG, just in case you want to swap it out for a gentler (albeit less persuasive) alternative.
Sprinco Gas Rings
As a consumable component, standard gas rings are fine. But we wanted more. Again, we turned to Sprinco’s superb quality for gas rings. And the market tells us that their cryogenically processed gas rings last much longer than standard rings. In pursuit of ultimate quality, reliability, and longevity, we insisted on Sprinco gas rings.
Nitride? No thank you.
Finally, we want to acknowledge a specific finish that we did NOT use in any of our BCGs, just so you understand that it was a conscious choice. We knew, out of the gate, that we didn’t want nitride in our BCGs, by any name (salt bath, QPQ, melonite, etc.).
Before we discuss “why not nitride?”, we have to acknowledge that the BCG lives in a very inhospitable environment. When a round is fired, the powder in the cartridge explodes, generating thousands of pounds of pressure, which puts stress on everything containing it (including the bolt head). The hot gas from the burning powder flows down the barrel, through the gas block, down the gas tube, and into the BCG. This blazing hot, high pressure gas flows through the gas key and into the carrier. The force from the expanding gas pushes the carrier rearward, pulling the bolt out of battery. As the bolt is pulled rearward, it rotates as the cam pin is forced along the groove in the carrier. As the bolt rotates, shear stress is applied to the locking lugs on the bolt head as they grind against the corresponding lugs on the barrel extension. As the bolt slides in the carrier, the metal gas rings scrape against the bore of the carrier to seal in the gas. As the BCG returns to battery, a few violent stress rock the assembly: 1) the gas key impales itself on the gas tube, 2) the bolt slams into the barrel extension, 3) the brick wall forces the the cam pin to grind along the groove in the carrier, 4) the movement of the cam pin forces forces the bolt head to rotate, and 5) the locking lugs shear against the lugs of the barrel extension. Everything about the BCG’s routine is violent and stressful.
Nitride is a conversion finish that results from infusing nitrogen into the surface of the metal. The result is a superficial modification that increases the surface hardness. However, this hardness comes at a cost.
While the nitride layer is harder than the bare metal, it is also brittle. This precludes it from a few place on our BCGs:
- The gas key features a relatively thin tube of metal. As mentioned, this tube experiences high temperatures and is impaled on the gas tube with every cycling of the BCG. When you weaken the inside and outside of a thin tube of metal by nitriding it, and you then subject it to extreme temperatures and impact stresses, you will see fracture long before you need to.
- The extractor is one of the most abused components of the AR. As the bolt strips a round from the magazine and slams into battery, the extractor pops over the rim of the case. Some finishes are particularly susceptible to chipping on this component. Beyond that, you don’t want a slick finish on this component (friction helps the extractor to hold on to the case rim).
- The bolt lugs are subject to significant impact and shear stresses during the camming action that results in the locking and unlocking of the bolt head into the barrel extension. The brittle nitride layer is more likely to chip than some other finishes.
Another problem that nitride presents for us is that it is typically used as a substitute for hard chrome. Why is that important?
Hard chrome is the Mil-Spec finish for the bore of the carrier and the lining of the gas key. The Mil-Spec calls for hard chrome for good reason. We walked through all of the stresses that are experienced by the BCG. A few of these are relevant to this chrome lining: the scorching hot gas, the high pressure, the friction of metal-on-metal, the impact of the gas key on the gas tube. So why chrome?
Hard chrome is an electroplated finish that is deposited on the surface of the metal. Is is extremely hard and durable, and (importantly) is temperature stable.
Conversely, the nitride finish becomes soft above around 900 degrees Fahrenheit. This is a relatively low temperature for the path of hot gas in an AR. While most shooters won’t shoot enough to get the BCG hot enough to soften the nitride, we don’t like the limitation.
In summary, we refused to compromise the durability and longevity of our BCGs with nitride, just because it is cheap and looks nice. Nitride may find a good home in some places on the AR; but our BCG is not one of them.