Chamfering Bore

[58weasel]

Some folks apparently chamfer the edges of the bore (say 30 degrees on the lands) as a finishing touch on the crown, after squaring the crown to the center line of the bore. Apparently as an alternative to a 11 degree crown. Is this a common practice? Is a special reamer or some sort required for this final touch? As this last operation on the crown is so slight, is it something that can be done with a hand tools?

 

[Erik Cortina]

It does not need to be done. It creates a recessed crown to protect the crown.

If your crown is good, leave it alone. They sell hand crowning tools, but I have never used them.

 

[Dans40X]

A "Q" Tip run around the bore at the crown will eliminate any doubt if there is a burr present.

A slight break can be cut to preserve a hunting rifle crown whether a sportsmans an 11degree or c'bored crown.

Accomplishing the task is easier in a lathe compared to using hand tools.

 

[WayneShaw]

I do it, whether the rest of the crown is 11 degrees, recessed or flat. I reach in and pull out a 30 degree to break the edge down to the bottom of the grooves. If you use a brush to clean, to me it makes sense pulling the brush back through. Never seen an issue with accuracy. And a razor sharp crown won't stay razor sharp anyway.

 

[58weasel]

Wayne
What specific technique do you use to get the 30 degree chamfer?
Thanks

 

[WayneShaw]

Always done in the lathe, bore dialed in just as close is if it were the chamber in, and use a razor sharp positive rake tool. Go in the bore, and use compound to cut pulling the tool out, never pushing the tool in.

I don't believe in these "lapping"methods for a crown. Anything you do to lap/polish a crown is pushing the edge back into the bore.