Sheesh!! I am the 800 lb. RELOADING TROLL!! Where the hell did the gorilla label come from?? Do you have Alzheimer's, Oldman??
Point #1: 20mm is far from a n00b. as such, he will tough, stinky, smell like burning Retumbo, which actually smells exactly like a diaper pail of diapers with pee in them. This is actually a fact!! Touch off a round of .338 Ultramag or .338 Lapua and you will get that distinctive PEE smell.
Not sure about the 270 in the 7.62x51 or .308. IIRC, the 270 is the 30-06 (aka) 7.62x63 necked down to 270, and not sure how you gonna get that in a 7.62x51mm chamber. I call fraud on 20mm for coming up with silly BS that can't be real for different reasons than the bullet vs. bore mismatch.