I like the 300 TSX for the 375HH as well. I have used it on a few big game or PG critters including deer, Blue WB and Kudu as well as Cape Buffalo all with reasonable success. But, one thing has always nagged at me.
All the other PG that I have hunted was done with a 308 or a smaller 7mm/08. And both rifles seemed to kill the thin skinned game more effectively than the big boomer does. Why is that? I cannot say that I know. My 375 gets great MV from the factory Barnes ammo. I chrono it at about 2580fps which is faster than the box claims (I have a 26" bbl on one and a 24" bbl on the other). I have only captured two bullets and both were from the Blue WB which are tough critters. They expanded to 2.0x and 2.2x at 180y and 10y range. So, I know they open up. They penetrate well also.
I cannot claim that the higher recoil is spoiling my accuracy as my 375's are some of my most accurate hunting rifles. My theory is that all DG ammo is designed with tougher projectiles to drive into and thru large tough animals such as Cape Buffalo or Elephant, etc and as such they must be able to plow thru large bones without breaking up. As such they tend to expand more slowly in thin skinned game and do less damage than some of the smaller 7mm and 30cal bullets which would never be called upon to stop a buffalo. My 308 with 180g Fusions was not really much faster than the 375. Runs about 2650ish fps. So, it is hard to say that velocity or energy is much of a factor. But, what it is doing with the available energy might be part of the difference. The 308 seems to do a lot of damage in the first 12-18" of penetration. All of the animals shot with it either dropped in their tracks or fall after running 40-60y max. 7mm was not as effective but many of those shots were a bit longer.
My long winded point is only that I am not a fan of using the DG calibers for deer or plains game unless you also specifically choose a proper bullet. The big bullets will kill them but there seems to be better options.
Notice that you never see a 375HH loaded with Hornady SST bullets or Nosler Ballistic Tips for example. Sadly nearly all of the factory ammo is optimized for DG if only to protect the mfg from repercussions should some nimrod try to kill an Elephant with a varmint bullet, lol.
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