The 300 H&H is one with which I've had a long standing love affair. I've always been drawn to classic cartridges and the 300 H&H was my first sort of custom rifle. I asked Remington's custom shop if they'd do one of their left handed KS Mountain rifles in 300 H&H. They said sure and about 8 months later, 4 days before deer season, it arrived. I grabbed some loads from my previous 300 and they shot great. A few days later I killed a decent little mule deer buck. Since then many deer, elk, pronghorn and caribou have fallen to the 300.
I used to use 150 and 165 grain bullets but as I've gotten older have come to appreciate the heavy bullets in any caliber. I shoot 220 grain Nosler Partitions in mine and am quite satisfied with their performance.
One of my old friends who hunted Africa many times owned two centerfire rifles, both pre-64 model 70s, one in 300 H&H and the other in 375 H&H. On one Africa hunt he and the guide were after kudu with the 300 when they stumbled onto a particularly nice cape buffalo. The guide asked if my friend wanted the buffalo. He said yes and took the shot with the 300 and a 180 grain Partition. The bull went about ten yards and fell over, its heart destroyed. The guide said he'd not seen one die that easy in a long time. I'm aware of the caliber restrictions in most areas, but this happened many years ago. I don't recall the country or if there were caliber restrictions there. The guide was well equipped with a stopping rifle in case things went sideways.
I could imagine life without many of my guns. Two that are staying with me as long as I can still draw breath are the 300 H&H and the 400 Whelen.