Crowning Improvments

[Boucher]

Steve Acker has an article on cutting a crown in the Dec/Jan issue of Machinist workshop. A little different technique taken from Grizzly’s Gordy Gritters chambering video is used.

There are many ways to cut a crown. The purpose is to help the bullet exit the bore in a uniform manner that releases the pressure from the bore without imparting unbalanced forces to the bullet. If the basics are accomplished the results are uniform enough that it is difficult to quantify the advantage of one method over another.

Surprisingly there are some really poor factory crowns. There are also crowns that are damaged in use by practices like setting the muzzle down on the floorboard of a vehicle. There are more barrels ruined by improper cleaning than are worn out from shooting. Many throats are ruined with the cleaning rod. The crown and muzzle are often abused similarly when cleaning from the muzzle.

These problems have been somewhat corrected with the introduction of bore guides and recessed or 11° crowns.

I would submit another technique for your consideration. Darrel Holland demonstrated this in some of his videos. It accomplishes some of what Steve is doing with his technique in a manner that is easier and helps with some of the cleaning problems. After what ever type crown you prefer is cut, Darrel uses the piloted center cutter to establish a small chamfer on the end of the barrel. This is only slightly deeper than the groove depth. This in turn assists the cleaning brush/patch to reenter the bore. I have had good results using this technique.

[rws]

Me too! I always pull a 60 degree chamfer in the crown. I think Obemyer (sp) was the one that kindof started this. I generally do the 11 degree, not because it's better or has an advantage, I just like it. You have to dial in the muzzle just as well as you do the breach end in doing this, but it makes a nice crown.

[Boucher]

Brownells sells these 11° piloted crowning tools made by Clymer.

Like the 60° piloted center tool they save the dialing in time. For several years that was my preferred style of crown. Over time I came to prefer the stepped recess with 60°chamfer shown below. The step tends to protect the actual crown and the simple facing cut was easier to do.

Stepped recess with 60 ° chamfer

[rbertalotto]

An 11 degree crown is nice, but it is difficult to do 100% perfect. The bore MUST be dialed in perfect to a depth of a couple inches or at least the length of the bullet you will be shooting, or the crown will be off center and accuracy will suffer. I've replaced a number of 11 degree crowns with a straight 90 degree crown and seen improved accuracy more than a few times. Lots of "gunsmiths" don't understand the relationship of that 11 degree angle and the last few inches of the muzzle bore.

A 90 degree crown is the easiest to do and the most precise as it does not require the bore to be dialed in perfectly. The last few inches of the bore simply needs to be running parallel to the center-line of the lathe. Since you are only cutting to a right angle, any slight misalignment is of no consequence.

But some of the best muzzle crowns I've ever looked at under a microscope did not even use a lathe!

Dave Manson make a hand operated crowning tool that does an amazing job. It indexes off the bore but it does not spin in the bore.' The secret are the cutters that were designed by Dave and some Russian aerospace guy.

It ain't cheap, but you could make a few $$ on a Saturday morning at the gun range charging $25 per crown!

http://www.mansonreamers.com/