Re: 175s for a Rem 5R?
more likely than not, you're going subsonic at that distance. Frankly, I'm surprised that it's working this well for you. Haven't used the Amax 168s much, but the Sierra 168 was originally designed as a 300 meter bullet, and was never intended for longer ranges. It'll work at 600, but it's running out of steam at that point. Most go transonic/subsonic at around the 900 yard mark. I can't picture the Amax as being that much better (a .230 vs a .218 BC) that it'd hang in there at these distances. The 175, on the other hand, was designed specifically to remain supersonic from a 308/7.62x51 at these distances, and with this length barrel. Not at all unreasonable to expect decent 1000 yard performance from that combination. Velocity of the Lake City M118 LR is up a bit over 2600 fps (2580 @ 78 ft), and it has no problems staying supersonic at the 1000 yard mark.
Give it a try, it'll work just fine.