If your rifle or handgun no longer shoots straight, the problem may nothing more serious than a worn muzzle crown. The only problem: It can be difficult to detect with the naked eye whether even a fresh from the factory crown is truly perpendicular to the axis of the bore. The good news: Re-crowning the barrel eliminates that possibility. In fact, right out of the box factory, firearms sometimes shoot more accurately after having the crown tweaked.
Besides factory new firearms, military surplus weapons often benefit from a refurbished muzzle crown. Consider the ubiquitous counter-bored Mausers and Mosin-Nagants currently being imported from Europe. Among their ranks, counter bores, which is where the first few inches of the rifling are opened up leaving clean sharp rifling, are common. There is no question they shoot more accurately than one suffering from a muzzle damaged due to a lifetime of whacks from a steel cleaning rod. Other than aesthetics though, muzzle crowning won't help counter-bored rifles.
Muzzle crown refacing toolkit, like those offered by Brownell's, are a quick and cost effective way to reface or completely form a precision, muzzle crown on rifle, shotgun and handgun barrel. No additional de-burring, lapping or polishing is required. Here's how it's done:
Safety first. Make sure the firearm is unloaded. Then secure the firearm in a vise in the vertical position with the muzzle pointing upwards. This because using a vise allows more precision cutting in a shorter amount of time. That said, without the availability of a vice, a partner can simply hold the barrel.
Heart and soul of this project is a pilot measuring the same diameter as a the bore. It keeps the cutter true to the centerline of the bore. Brownells offers a broad selection of different diameter pilots to fit different bore sizes.
If muzzle is rough, severely worn, or otherwise damaged, face the muzzle, making sure it is square with an L-square. Either true it to shape with a mill file, or a 0-degree cutter.
I you are bubba-ing a Mosin or Lee-Enfield by shortening the barrel, here's a tip: Place hose clamps on the barrel to guide the hacksaw so the cut is at least close to true. Then file the shape before proceeding with the Brownell's muzzle cutter.
Place the cutter on the pilot and secure it with the kit's included Allen wrench. Slowly lower the pilot into the muzzle. Maintaining downward pressure, slowly turn the cutter clockwise. Make several turns being sure to use a few drops of cutting coolant/lubricant while cutting. Periodically remove the cutter and inspect the muzzle. If more cuts need to be done, repeat until the muzzle is free of all imperfections.
Once faced and squared, make a few more turns of a cutter with light, downward pressure in order to lend a final finish without removing much material.