A few years ago, I was at a gun show and an older gentleman was divesting himself of his M95 rifle and all associated supplies. Since the prices were reasonable, I bought his entire rig. Included were a number of boxes of bullets. One such was a box of Barnes XBT bullets. These are the solid copper bullets. Since Barnes does not make a .330 bullet for loading 8x56R, the old gentleman had carefully taken each of these .338 bullets and turned it down to .330 on a lathe. Back when a box of 100 Sierra or Speer bullets cost $14 a box of 100, these cost $35 for a box of 50. The XBT is no longer made, but its replacement costs over $41 a box now. Actually, the percentage of increase of Barnes bullets has been less than other brands. Perhaps this is because they were so high-priced to begin with, they figure if they raise the price much higher, sales will suffer.
The blue coloration on most of these bullets is due to the fact that they used to be teflon coated. The teflon on the bullet shanks of course got turned off in the re-sizing process. These started out as 185 grain bullets and now weigh 176 grains.
Because copper is less dense than lead, Barnes bullets tend to be longer than their conventional lead core jacketed counterparts in corresponding weights. This makes the lighter weight in a line more accurate. The longer the bullet is the better its ballistic coefficient is, up to a point. Supposedly, a longer mass will have a lower ballistic coefficient which should result in greater accuracy. Now that these bullets have .008 shaved off, they theoretically have an even lower b/c.
Some other thoughts come to mind with this fancy bullet. These solids were made to be driven hard in a .338 magnum. Obviously that kind of power behind the bullet isn't going to be there with the 8x56R. There's another coefficient to think of with this solid bullet, and that is the coefficient of friction. It is assumed that the solid copper bullet would have less give than a conventional lead core jacketed bullet, and therefore a higher level of friction. Going on that assumption, when I have used these bullets, I loaded them at medium levels of slow-burning propellants. The slow burners have a more gentle pressure curve, kind of easing them into motion instead of slapping them as a faster powder might.
Of course the whole idea behind the solid copper bullet is to provide maximum penetration with minimum deformity to the bullet and retention of bullet mass.