I am getting ready to start playing with a 300 H&H and I have about 130 of the 165 Gr GMX on hand. I know they discontinued them in favor of the CX but like I said I have them on hand and figure they would be a good deer/pronghorn bullet. Loading data for the GMX is a little hard to get since they discontinued them so I'm seeing if anyone has a pet load or even a starting load? I have nearly 4 lbs of IMR 4831 on hand so would like to use that powder but I also have 4350, RL-22 and several others that I use in my 7mm Mag and 375 H&H Mag. I have been told that you can use CX load data but don't know if that is valid. Any info anybody can provide would be appreciated.

I am also curious if the Barnes data would be comparable enough to use as a starting point?

That is what I would do. Just start low and you should be ok. Also look at Nosler they show a few different powders that you may have.

I loaded the 165’s in my 300 wby. Shot good. If you hit bone they do great if you don’t hit bone I never got much expansion. I used Barnes data for a starting point if I remember correctly.

Nosler though a different bullet is geared toward the bullet of that gr weight with the toughest construction so good point for data. Barnes can be another good source if the bullet maker makes one similar. Compare data from several sources and start with the lower or average is what I have done in the past.

Deer and pronghorns do not really call for that tough a bullet IMO unless running very fast but when you have them go for it if you want

I load for 2x 300 H&H's (a Rem 721 and an Enfield P14 custom build). I have gotten excellent performance shooting 168gr Barnes TTSX and 180gr Barnes TTSX. The CX and TTSX are pretty comparable, and even going to the max barnes manual loadings I havent seen any pressure signs or had any performance problems at all.. I think youd be safe using the barnes data as a starting point..

Do the Hornady bullets have the pressure relief grooves like the Barnes bullets do? that can make a difference. I think Hornady and Nosler use a gilding metal bullet as opposed to just copper as well. Just thought about that.

The old Barnes bullets before the TSX bullets load data for was lower. I remember loading the old Barnes bullets hack when and they reached pressure at lower charges than cup &core bullets or Partitions.

If I remember right the gm had 2 pressure groves.

CX does too, and both have two to be exact. I looked because i was curious if it was same as barnes

I hunt alot w a .300 H&H, have hunted w 150, 180, and 200 gr Barnes TSX. My best loads for each:
150 RL -15 61.0 gr
180 RL-19 69.0
200 IMR 4350 62.0