Hello all,
I'm sitting here looking at some fired cases and a chamber cast from a .338 LM that I'm playing with, and trying to figure out why the numbers don't add up.
Fired neck outside diameter of .370 at the case mouth, and .373 at the neck/shoulder junction. Measured neck thickness averages out to 0.014 (measured with a Mitutoyo ball mic) so by my math, 0.370 - 2(0.014) = 0.342. Fired case neck ID measures 0.338?!? A bullet (.338 SMK) will not drop into the case mouth, but can be pushed through with mild finger pressure - so I tend to believe the ID measurement. It acts and feels about like if one were to try for 0.001 or less neck tension and soft seat the bullets - but this is *fired* brass.
The chamber casting measures 0.3737-0.3739 right at the end of the chamber mouth, as best I can tell with a Starrett mic.
What am I missing here? The casting seems to indicate the case should be expanding more than it is. The fired OD and thickness of the neck don't seem to agree with the measured ID. Either I suddenly forgot how to use a set of calipers and a micrometer, or something very odd is going on here.
Brass is Hornady, from factory ammo fired in this gun. Counting the initial loading as 1x, this brass been fired 6x in this gun, and I've been scratching my head over the apparent disconnect in the measurements the entire time - i.e. it doesn't seem to be something related to the brass work hardening through sizing/firing repeatedly. Most recent firing was some fairly light loads, but I've also fired some pretty warm stuff down it to (both the original factory loading, and some during load development since). No appreciable difference there either.
Any help would be very welcome.
Monte
I'm sitting here looking at some fired cases and a chamber cast from a .338 LM that I'm playing with, and trying to figure out why the numbers don't add up.
Fired neck outside diameter of .370 at the case mouth, and .373 at the neck/shoulder junction. Measured neck thickness averages out to 0.014 (measured with a Mitutoyo ball mic) so by my math, 0.370 - 2(0.014) = 0.342. Fired case neck ID measures 0.338?!? A bullet (.338 SMK) will not drop into the case mouth, but can be pushed through with mild finger pressure - so I tend to believe the ID measurement. It acts and feels about like if one were to try for 0.001 or less neck tension and soft seat the bullets - but this is *fired* brass.
The chamber casting measures 0.3737-0.3739 right at the end of the chamber mouth, as best I can tell with a Starrett mic.
What am I missing here? The casting seems to indicate the case should be expanding more than it is. The fired OD and thickness of the neck don't seem to agree with the measured ID. Either I suddenly forgot how to use a set of calipers and a micrometer, or something very odd is going on here.
Brass is Hornady, from factory ammo fired in this gun. Counting the initial loading as 1x, this brass been fired 6x in this gun, and I've been scratching my head over the apparent disconnect in the measurements the entire time - i.e. it doesn't seem to be something related to the brass work hardening through sizing/firing repeatedly. Most recent firing was some fairly light loads, but I've also fired some pretty warm stuff down it to (both the original factory loading, and some during load development since). No appreciable difference there either.
Any help would be very welcome.
Monte
