I think the biggest problem are a lot of guides and Texas hunters don’t understand ballistics and proper bullet construction for the job and don’t understand the difference in vital location. I’m willing to bet a large majority of their hunters use a cup & core type bullet, go cheap on ammo and/or use the same bullet they use for their Texas Whitetail. I’ve me more than one guide (including for nilgai) who doesn’t like an exit wound or finding the bullet under the off side hide and has suggested something that grenades like a ballistic tip/berger, or your std Corelokt and American Whitetail.
l’d suggest a heavy for caliber, premium bonded or mono-metal bullet. If you shoot your 7mag well, shoot a heavy 175gr bonded/mono metal bullet so you get an exit and break both shoulders when you punch for the vitals. I’m always an advocate of making additional holes until your animal is on the ground. I’ve double tapped more than a few animals and learned that lesson the hard way.
Personally, I’d grab my 300WM or 375 but I like both and am very confident with them. I have zero love for a 7mag. I sold my 338WM to a buddy specifically for a Nilgai hunt, but that would’ve been a good option.