I hear ya Sir!
The largest "sporting rifle" I've shot is my Ruger No.1 S.S. .458 Lott. I can shoot aroud 8-10 rnds off the bench with just a T shirt then the headaches start and my accuracy falls off!

I've shot numerous .50 BMG's but as you know their so heavy its just not the same as a sporting rifle of normal weight.

I would love some day to shoot someones .600 NE but I know of nooone in my general location of S.W. PA who owns one.

Thanks for adding to this topic Sir!!
Take care,
Chris