Just for clarification, the 175 was designed at the request of LCAAP when they were developing the M118LR ammo some years back. The weight was set by them, with (as I recall) a limitation of the finished bullet to be between 150-175 grains. The old style 180SMK was an excellent Long Range bullet that was much favored by USAMU when their teams were still shooting M14s in 1,000 yard competition. Since it was redesigned with the short boat tail (same one used on the 168), it became essentially useless. The AMU continued to use the old style 180 SMK for some time afterwards, and there were special runs of the old style bullets run specifically for AMU contract orders. The 175 was basically an attempt to match the ballistic properties of the original M72/M118 bullet, the 173 grain FMJBT. Very good bullet out to 1,000 yards, but didn't have the accuracy of the OTM designs. The finished product pretty well accomplished that goal, and has been the standard bullet in the M118LR bullet ever since.
While the 155 Palmas do have a similar BC, they can be a bit more problematic than the 175s. They (Sierra) had to violate several of their basic guidelines of bullet design to arrive at this bullet. The bearing surface of less than 1 caliber is a primary example. These bullets shoot very well in barrels, chambers and throats that are specifically set up for them. This usually entails a tight bored (.2985" is common) barrel, with a short throat and a 1x13" twist, normally finished at about 29"-30". They need this to achieve the 2950 fps that is required to reliably keep these bullets supersonic at 1K. In shorter barrels, or conventional .300" bore guns with somewhat faster twists, they may, or may not shoot as well as the heavier bullets. But chefcam864 is perfectly correct here; we don't use 155s because they're the best bullets for this job (they aren't) but because that's what the rules require for this game. Note that most US shooters who build "Palma" guns that they don't intend to use in matches governed by International Palma rules, usually go with faster twists, and use heavier, higher BC projectiles. Like I said, they're what the rules require, but not what is necessarily best.
