Why You Should Use the BCM AR15 Bolt Assembly

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Last Updated on January 12, 2021.

So far, I’ve only purchased one complete AR-15 rifle. That was over ten years ago. All my other AR-15 rifles were built from parts. I’ve used at least one BCM AR15 Bolt Assembly in all of them, as the primary bolt or as a backup.

I’ve shot thousands of rounds (maybe tens of thousands, at this point) with my BCM bolts. And I’ve never had an issue with any of them. That’s why this is one of my favorite AR-15 bolts.

This isn’t the only bolt I’ve used. And I’m not a BCM fanboy who thinks that everything BCM makes is amazing. Some BCM parts seem to be weak links in BCM’s product line.

But I find the BCM AR15 bolt to be basic and reliable. That makes it easy to recommend to just about everyone, so long as they don’t need anything special.

With that in mind, here’s my experience with the BCM AR15 bolt assembly, featuring the bolt from my primary 14.5 rifle.


The first selling point of this bolt, for me, is the steel. This bolt is machined from Carpenter 158 steel. I know that’s not a selling point for some people. But I prefer Carpenter 158 steel bolts. Here’s why.

I’m aware that there are plenty of high quality 9310 steel bolts out there. I also know that it’s possible for high grade 9310 steel to be stronger than Carpenter 158 steel, if it’s heat treated properly.

However, there are many suppliers of 9310 steel. And there’s some variation in the composition specifications for 9310 steel. Most notably, a common composition spec for 9310 steel is that the steel has 0.08% and 0.13% carbon.

Based on my reading of metallurgical engineering books (which is admittedly not enough for a metallurgical engineering degree), more than 0.10% carbon starts turning the steel into some grade of carbon steel, which is more brittle than steel with less carbon.

So it’s possible that a 9310 steel bolt could be too brittle, depending on the supplier, the production batch, and the heat treatment.

On the other hand, Carpenter 158 steel is proprietary steel that only Carpenter produces. And the carbon value is set at 0.10%.

Carpenter also specifies the percentage of other elements like manganese and silicon. Many 9310 steel suppliers have acceptable ranges for these elements as well, rather than set values.

Basically, all of this comes down to fewer variables. There are fewer variables that affect quality in Carpenter 158 steel bolts. So I prefer them over 9310 steel bolts.

However, it’s worth noting that there are plenty of companies that make very strong 9310 steel bolts. And I’m not saying you should never buy a 9310 steel bolt.

It’s just that I feel more confident in Carpenter 158 steel bolts because there’s less variation in the production process. And the BCM bolt is Carpenter 158 steel. So I like it.

And, the lifespan of my BCM bolts seems to indicate that Carpenter 158 steel works pretty well.


This bolt sports a phosphate finish, which is the mil-spec coating. It’s good enough for government work. And, as it turns out, the phosphate finish is good enough for a lot of other work as well.

But seriously, the finish on this bolt is pretty solid.

Yes, it’s got the usual splotchy sort of look that most phosphate finishes have. However, it takes quite a bit of shooting to wear through to the silver metal. And I’ve never found any rust or corrosion on my BCM bolts.

The finish might not be the prettiest. But it works the way it should. And that’s the important part.

Quality Control

BCM is known for excellent quality control. No, it’s not perfect. And, BCM’s customer service department was recently caught delivering poor customer service. That’s not a good look, I know.

However, BCM customer service gripes aside, this bolt is both high pressure tested (HPT) and magnetic particle inspected (MPI).

Essentially that means that they fire a high pressure 5.56mm round (M855 or M193) with the bolt, then they perform the magnetic particle inspection.

This function checks the bolt, then magnetically inspects the bolt for deformation and cracks. It’s the standard quality control procedure for mil-spec bolts.

Many AR-15 bolts are only magnetic particle inspected. A bolt that’s only magnetic particle inspected is usually less expensive. It’s not cheap to do the high pressure test.

The magnetic particle inspection is probably adequate. But I feel more confident in a bolt that’s been through both HPT and MPI. An added layer of quality control is better, in my mind.

Maybe I’m just paranoid. But I find the quality control behind the BCM AR15 bolt to be comforting.

Broken Bolts

As I mentioned earlier, I’m not a BCM fanboy who thinks everything BCM makes is great.

One BCM component that I think is not so great is their bolt carrier. I’ve mostly purchased all my BCM bolts as a standalone bolt assembly.

Whenever customers bring BCM bolt carrier groups into the shop with problems, it’s usually the bolt carrier that’s causing the problem.

Also, I find the BCM bolt carrier to be kind of expensive. The bolt carrier alone costs about $100. That seems a little steep when you can get a complete bolt and bolt carrier for less than $100, and it will probably work just as well.

Unfortunately, it can be tricky to find the BCM bolt without the bolt carrier, since they’re often sold together.

But, rest assured that it’s a small number of BCM bolt carriers that cause an issue. And, if you need to replace the bolt carrier, there are plenty of affordable options.

Releasing the Bolt

In conclusion, I’ll reiterate my initial statement: the BCM bolt is basic and reliable.

Yes, that means there aren’t any bonus features or performance enhancing drugs in this bolt. But it will run reliably for many thousands of rounds. And it’s pretty well priced for a C158 steel bolt that’s been high pressure tested and magnetic particle inspected.

Ultimately, I’ve shot a lot of bullets with this BCM AR15 Bolt Assembly. And it lives up to the BCM reputation, whether that reputation is well deserved or not.