Re: 6.5 155 MK
I used a lot of the 155s up until '97 or so. At that time the lots were going down in QC as compared to the previous lots. The first lot was an excellant bullet BTW. The 142s are still a very very good quality bullet and the BC isn't that far behind the 155 anyway. I still use my 155s once in awhile in my 6.5-300 for hunting for a little more energy, but nothing serious in regard to accuracy.
I can't speak for any of the newer lots than '97 though. They might be better than what I have, but it would take a damn godd bullet to out perform the 142s IMO.
Also you need an 8" twist for these bullets. A 9" will not cut it. I've fired 5" groups at 100yds with them in a 9 twist. Never tried a 8.5" so that may work. Not sure what you already have for twist. And because these bullet are so long if you are not throated long they suck up a lot of boiler room space and keep your velocity down and pressure up because of that. My 6.5-300 is throated for the 155 and I can't seat a 140gr class bullet to touch the lands.
My thoughts only. FYI: if you and WyoWhisper aren't doing anything out there the weekend of Sept 25,26,and 27 I'll be competing at the Colorado Rifle Club that weekend in Byers, CO. It's the NBRSA National Championships. Come on over and say hey if your around. You can see a lot of different rifles and optics at one time. There will be shooters there from all 3 santioning bodies. A beautiful range to fire at also.