Hi Nick,
No mystery at all here; the 155s were designed for 1000 yard performance, where the 167s (and the 168s) were designed for 300 meters. The 155s actually have a better BC than the heavier bullets, and can be driven considerably faster. As a result, they can deliver far superior performance at long ranges as compared to the 167s or 168s.
In general, the rifles set up to use the Palma bullets (the 155s) are at their best with a 1x13" twist, a somewhat tighter than normal bore and groove dimension, and a shorter throat, such as those cut by a Palma reamer. Most of these rifles also run 29"-30" barrels to maximize performance and velocity. Generally speaking, you'll need something on the order of 2,925-2,950 fps at the muzzle to ensure that the 155s stay supersonic all the way to 1,000 yards.
The 168s were the odds on favorite for HP-XC competitors for many decades, but they were never very good much past 600 yards. In bolt guns, most shooters used the 168s at 200 and 300 yards, and then switched to 190s at 600 and 1,000 yards. Those Service Rifle shooters using the M14s (M1As) generally went with 168s at 200 and 300, with some staying with them at 600 as well. Many of us switched to the 180s (old style; the new 180 SMKs are garbage) at 600, while virtually everyone (shooting service rilfes)shot them at 1,000.
Hope that helps.
