Do you, or have you used IMR 4320?
 

What caliber/load do you use it for? And what works good?

Many years ago, I tried IMR 4320 for loads in my .30-06 and .308 Win. Velocity and accuracy wasn't good enough so I didn't pursue it.

I use 4320 in my daughters Rem Model 7 .260 with the Sierra 120gr Pro Hunter. It's very accurate and consistent in her rifle and has become our go to powder for the 260. I also have a friend who uses it in his 7mm08 with good results.

IMR 4320 is one of my favorite powders. I use it in .220 Swift, 22-250, .243, and I even use it for practice loads in my g/f's .270. It seems to be very accurate and meters very well. It is not terribly popular, but these days it seems to be just as difficult to find as the more popular powders.