Sniper Country Duty Roster collective wisdom


Technical - Muzzle crown:


Looking for a little help. After cutting a barrel to the length desired what is the big deal between a step type crown and having a target type crown. The rifle is a 24" long 1-8 twist Hart barreled .223 and will see mostly field use and a little bench use in an informal league. Any advantage or disadvantage to either???
Todd <duckman@eznet.net>
Andover, NY, USA - Thursday, February 25, 1999 at 00:59:24 (ZULU) 


Re: target type crowns

Todd,
When someone says "target type crown" they really mean a crown machined with precision in mind. It really does not mean a particular type, although two types are normally used. One is the 11° cone crown and the other is stepped (two 90° planes separated by a small distance). This is hard to describe in a few words.

As long as the gases escape evenly around the base of the bullet, then any type will work fine. It is said that with boattail bullets that the crown in not as important as it is with flat base bullets. I know of no study one way or the other on this.

I've crowned my barrels at 11, 12, and 13 degrees and also the two step design. All seem to work equally well. The stepped type crowns are not as critical as far as centering the barrel as the cone type demands. I've read this and can picture it in my mind.

When "indicating in" a barrel for crowning, I key of off the grooves, and want to see no more than .0005" (.0127mm) of runout, and .0002" (.00508mm) is much better and is what I strive for. If one looks closely enough, it will be found that the grooves and the lands have their own centerlines, Now for chambering I key off of the lands. This keeps the "push" fit pilot running true and not orbiting. Working at "tenths" (.0001" or .00254mm) is tedious and the better part of an hour can be used in just dialing in just one end of the barrel. This is not a hurry up job.

Although some chamber and crown between centers, but this is not the way I do it. I prefer the rigidity of the headstock to hold the barrel. Both methods have their advantages and disadvantages. Both techniques can build winning rifles.

Some gunsmiths break the crown's interior sharp edge with cutting tools or a little lapping compound on a brass ball. This strengthens the corner and may be important for tactical use. I prefer to leave all my crowns sharp and they are very easy to inspect for wear or damage. If the corner edge reflects any light at all, then something is suspect. This is just like checking the sharpness of a kitchen knife.

Some people cut towards the bore, but I always pull my tool away from the bore. The cutting tool is hand honed and has a large amount of rake and relief. It cuts the barrel material like butter and no burrs are raised in the bore. This is checked by dragging a Q-tip across the barrel exit while watching closely for any fiber snagging.

This is more than you wanted to know, but I'll bet each paragraph could be expanded into a page without too much trouble. Much has been left unsaid.
Ron N.

Ron N. <rcn8@accnorwalk.com>
USA - Sunday, February 28, 1999 at 01:16:18 (ZULU) 


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