shinny: I'm not knowledgable or skilled enough to know why, but after using a 6ppc with the .262" chamber neck, and when the barrel was due for replacement, I thought like you and had 2 barrels cut with .272" chamber necks. They are both very good. Then recently bought a used, like new 6ppc, also with 2 fitted barrels and chambered with .262" necks, so I'm back to outside neck turning to .0085". Comparing them side-by-side, the .262" vs .272", and the .262's always come out the winner, sometimes by only a very little, but still better. The .262's have been at the top since 1975, so their long time record speaks for itself.