Probably 15 years ago at this point, but when I was a young man (i.e. dumber than I am today), I really wanted the biggest and baddest rifle that could "do it all", and the 300 RUM had just come out. I somehow managed to find a Remington 700 Sendero chambered in it on the shelf, and immediately grabbed it. 
I also thought it "unmanly" to put a brake on the gun; I should be able to handle it as is. What a horrible mistake that was. Shooting those 'no recoil pad having' HS stocks of the era with an ubraked 300 RUM off a bipod was profoundly stupid. That thing gave me a flinch that I'm still not entirely over. Even with my F-Class guns, and little 6mms I'll occasionally catch myself flinching. 
My advice: 
Double up on hearing protection. It works wonders. 
Avoid caffeine before shooting; I don't follow this advice, but when I don't have any, I'm WAY less jumpy. 
Go shoot a lot of .223
Dryfire. 
This will sound crazy, but it actually worked the best for me....When I still shot at public ranges I would get next to someone who was shooting with the nastiest brake. Get on your rifle and start dryfiring/concentrating like you're going to shoot, and just get peppered with blast...the more the better.  After 10-15 minutes of this, it was like you acclimated to the noise/blast and follow-through was much better. 
Good luck!