What is Concentricity?

If you’re going to attach anything to your muzzle, having straight and concentric threads is crucial. Simply put, concentricity means the outside of the barrel lines up with the bore. Why does this matter? Let’s see.

The Wobble Factor

When setting up a barrel in a lathe for threading, more than half the time the bore is centered, but the outside diameter of the barrel wobbles. This means the distance from the bore center to the barrel surface isn’t consistent. Another way to say this is the bore was drilled off-center.

Not getting too deep into barrel manufacturing processes, this isn’t a big deal—until you thread.

Why Concentricity Matters

Should you care? Yes. Here’s why:

“A bullet traveling down the barrel exits the muzzle and continues in a straight line from the bore. Any attachment off-center could not only ruin accuracy but also be dangerous.”

Off-center threads could put uneven pressure on attachments and be dangerous.

The Solution: Proper Lathe Setup

The solution is proper lathe setup:

1. Indicate off the bore: First, center the bore so it spins perfect in the lathe.

2. Cut the outside diameter: Next, cut the outside of the barrel to match the bore evenly all around. At this point the barrel is concentric.

Threading and Final Steps

Once the barrel is concentric, then determine the correct outside diameter to match the threads. From there you can thread. Read more about thread pitch here.

Concentricity in a Nutshell

In the end, concentricity means the bore of the barrel lines up with the outside surface. When you thread it, it lines up with the bore too.

“Does it matter? By now you should know the answer: Yes, it does. Concentricity is key to performance, safety and accuracy.”

And that’s concentricity in a nutshell.