Bullet RPMs and barrel life

Stealeded this from a discussion on FB. Fascinated for those of us who shoot. If you do not shoot, this is incredibly boring.

The final statement by John is a mind-blower.

Expected barrel life, 3 shots.

BILL: Worthless Info # 3,225! 

Has anyone ever wondered what the RPM of your bullets are coming out of you 45/70’s for example???

405 gr slug for example:

Well, let’s figure a 1 in 20 twist rate. 

That means for every 12” of barrel your Bullet twists .6 revolutions. 

. 6 x 1,600 feet per second = 960revolutions per SECOND. 

960 x 60 seconds = 55,296 RPM!!!!

That, my friends, is SMOKIN for that size slug. 

Now imagine a 3k FPS round with a 1/10 twist rate????!! Wow

GARY: Of course the bullet is only in the bbl a very short time, not minutes and as soon as it leaves the bbl it slows down, all are aware of that.

SAM: The spinning won’t slow down as fast as the forward speed. When Hatcher did his experiments of shooting bullets straight up in the air they returned base first.

MICHAEL: Also, watch this video on shooting at ice to stop the forward movement of the bullet, but it does very little to slow the rotational velocity. It sits and spins like a top for over a minute. If it takes this long with direct contact with a solid to lose its rotational velocity, the short flight time of a bullet only contacting a gas has essentially no effect. https://youtu.be/UwIpv94GPt4

JOHN: Interesting, Next time someone asks you "What's the life of this barrel?" Instead of telling them something like 10,000 rounds tell them the life of the barrel is "about 7.5 seconds." After all, a round going 2,000 ft/sec only spends .00075 seconds traveling through the barrel so 10,000 rounds would only add up to 7.5 secs. Puts things into perspective doesn't it?