It makes a helluva noise, and packs a helluva wallop."
The ad showed a close focus of a M70 muzzle, (hooded sight and all) with all else blurred in the background.
60's power-marketing at its finest.
"I have always disliked the words 'authority' and 'expert' when applied to those who write about guns, shooting,and hunting. I have never set myself up as either." Jack O'Connor
There are certain "must shoot in 1:8 or faster twist" bullets--e.g., 130 Gamechanger, 135 Berger--that will stabilize fine in 1:9 rifles assuming you check the appropriate boxes in the calculator, e.g., velocity, altitude, temp.