how to state rifling depth

[RhodeHunter]

When someone says "typical round ball rifling is between .010 and .016", do they mean per side, or do they mean the difference between the bore diameter and the groove diameter?

My Deerstalker .54 has this in the book that came with it:
Bore: .542"
Groove: .558"
- the difference is .016

So do you say "the rifling depth is .016?" or do you say "the rifling depth is .008" per side?"

I always assumed the ".010 to .016" was per side.

Just looking for the proper way to speak about rifling depth.

[Naphtali]

Rifling depth, when stated as you illustrated, is depth per groove.

Hope this helps.

[405]

Agreed, there is much confusion on this. Don't assume anything. Always surprises me when folks even on this forum interchange or go fast and loose with the terminology "bore" and "groove" diameters. Just have to read the description with care. Or ask specifically about the numbers when talking to someone. When in doubt pin it down further and measure. For your example, the groove depth (not rifling depth) on your Deerstalker 54 is .008. Think of it this way: the word rifling is a general term that usually describes the spiral pattern of lands and grooves in a rifle barrel. The land to land diameter is the bore diameter

[oldracer]

I would suggest slugging the barrel and then measuring the larger diameter which is the rifling diameter and then measure the smaller diameter which would be the bore. At least that is what Doug told me to do as he said never to trust the dimensions that came with a gun or barrel.

This has proved true as my Hawken muzzle loader has a slight taper to the barrel at the muzzle which the documents said nothing about? My Leigh muzzle loader is straight as can be?

[405]

I would suggest slugging the barrel and then measuring the larger diameter which is the rifling diameter and then measure the smaller diameter which would be the bore. At least that is what Doug told me to do as he said never to trust the dimensions that came with a gun or barrel.

This has proved true as my Hawken muzzle loader has a slight taper to the barrel at the muzzle which the documents said nothing about? My Leigh muzzle loader is straight as can be?

The word "RIFLING" is a general term that describes the spiral pattern of the lands and grooves in a rifled bore. The land to land measurement is the bore diameter. The groove to groove measurement is the groove diameter.

[RhodeHunter]

I would suggest slugging the barrel

Yes, I recently slugged a barrel and that is what got me into this question, as I wanted to be able to interpret my results and compare with other figures I have been coming across, as well as to be able to speak about it properly.

[RhodeHunter]

405 and Naphtali, thank you. Or as Austin Powers would say, "Groovy baby".

[RhodeHunter]

I just read in "The Art of Building the Pennsylvania Longrifle" by Chuck Dixon, Dave Ehrig and Dave Miller, that...

"...good patched-round-ball barrels of today will have a groove depth of 8000ths to 12000ths of an inch." originally published in 1978

[405]

:) if that's a direct quote, looks like he mixes numeric notation and text. I suppose he really means to say groove depth of, .008" to .012"

[RhodeHunter]

I agree.