No, this is not a pro-monarchy article. The crown is the area at which a bullet leaves the muzzle of a barrel. Protecting the crown is important for accurate shooting.

Caveat: I’m not writing from a position of authority. I picked up a new hobby, and writing short articles is a way to document my learning, and encourage further study.

At the moment the bullet leaves the crown immense pressure is released (the rapidly expanding gas that has been driving the bullet through the barrel). If the crown is less than perfect, this pressure will not escape in a clean, uniform manner. Any asymmetric spike in pressure will shove the bullet, causing a significant deflection from the desired trajectory.

Damaging the crown

Accidental damage

Obviously, accidents are one way a crown may be damaged. If you watch any halfway-decent marksman or sniper movie, you can expect a scene where they display how much they care about their rifle: going to lengths to protect their rifle during a fall, or berating someone for carelessly handling a rifle.

If a rifle is dropped, and the muzzle strikes something hard, the crown may be damaged. Even a small dent or bur can negatively affect precision to a significant degree. It’s not uncommon for a rifle barrel to have a slightly recessed crown to help protect it from unintentional knock damage.

Inattentive cleaning

To continue to produce precise shots, a rifle barrel requires maintenance. One cleaning technique involves using a long cleaning rod, with various attachments, to brush and treat the bore. If care is not taken, as the end of the cleaning rod exits the muzzle, it may wear a small patch of the crown at the six o’clock position. Over time, and habitual cleaning, this wear may harm the crown’s integrity.

Making my own crown guard

As mentioned above, a gunsmith or rifle manufacturer may slightly recess the crown to help protect it. However, there is a less common variation to rifle barrels called a deep hole crown. A longer barrel has a wide, smoothbore section at the muzzle, which recesses the crown up to a few inches inside the end of the barrel - the crown is inside a deep hole.

There are multiple theories why this style of crown may be desired, but I’ll focus on the side effect that it makes it more challenging to be mindful of the crown when cleaning with a rod. To help manage this issue I dusted off some CAD skills I hadn’t used since high school, learnt about 3D printing, and made a small plastic piece to help protect the crown during cleaning.

I used some in-browser CAD software, Onshape, to draft the piece. Then used the impressive facilities at my nearby library to slice and print the design (slicing is where software takes the 3D model and turns it into layered instructions for the 3D printer). I use this insert when cleaning to provide a little extra guidance to the cleaning rod as it exits the crown. I’ll likely iterate on the design as continued use gives me ideas for improvements.

deep hole crown guard