Are the new CX bullets just a refined model of the GMX,or something altogether new..

More refined I think. The CX has less drag. They have (had?) a pretty good video about the CX and how wonderful it is on their site. I asked Horn. about not having any load data for the CX and they told me to just use the GMX data that was in their last reloading manual.

I am using the 180-grain CX bullets in a .300 Win Mag and the 90-grain .257 CX bullets in a .250 Savage. The 180s are by far the most accurate bullets I have used in the .300, and the .257 90-grain bullets equal or beat everything else I have tried in the .250 Savage. I have only shot one animal with the CX, a big cow elk with the .300 at just over 300 yards. The bullet entered just in front of the left hip and was found under the skin just under the right shoulder. Weight retention was about 97% and the bullet had expanded to just over 1/2-inch. Based on the two guns I have tried them in, I bought a box of the .308 165-grain I plan to try for my daughter's .30-06 and a box if the 250-grain .375 bullets to try in a .375 H&H Magnum

Glad to hear the 180 CX are shooting so well.

I just got some 165 gr,and will try them in my 300 Win "weather permitting" (as shooting in the cold and snow is not much fun).

I just finished working up a load in my 6.5x55 with the 120 grain CX. I am getting half inch groups at 100 metres. Not too shabby.

I suspect poor accuracy in GMX is why the CX was developed. My R8 Blaser 300 Winmag shoots 180 grain GMX very accurately. My friend's R8, same caliber, same barrel profile is very inaccurate with them. CX shoots well in both barrels.

Resurrecting this thread.
Just how tough are these CX bullets?
GMX is not known as being particularly tough, but is the CX an improvement?
In the league of the Barnes TTSX?

I have no experience of these.

It both seem to be made of copper with a plastic tip.

Should be tough enough!