05-14-2014, 02:58 PM
bwaites Wrote:Generally speaking, all other things being equal, the larger the powder capacity vs the barrel bore diameter (called "overbore") the faster erosion takes place. A Grendel with 35 grains of powder capacity will last longer than a 6.5x47 which will last longer than a .260 Rem, which will last longer than a 6.5x284.
[/url]
The reason that I asked is that General Dynamics reports improved machinegun barrel life with the .338 Norma (over the .338 Lapua) even though the difference in the volume of the two cases is small. If the loadings match those in the NDIA presentation above, the propellant difference is only 1%
Only one article that I have read suggests that other factors come into play. In this article (from the same site you referenced) one shooter expressed his thoughts that a long case neck could reduce barrel wear. He postulated possible reasons:
- Reduced blow-by since the front of the bullet shank could be fully engraved before the back exits the case.
- The longer case neck helps align the unburnt particulates leaving the case. This in turn reduces the amount of particulates laterally impacting the barrel throat.
I have never seen a confirmation of either of these effects, but the author claims that the relatively long-necked 6mmBR demonstrates them.