The 20 mm caliber is a specific size of cannon or autocannon ammunition.
There are few weapons (aside from shotguns and large game hunting rifles) which have been built that fire projectiles between .50 caliber (0.50 inches/12.7 mm, roughly 13 mm caliber) and 20 mm caliber, though the 14.5 mm caliber is used by some Soviet machineguns such as the KPV and anti-tank rifles such as PTRS, PTRD, and NTW-20.
A very small number of anti-tank rifles have been produced in 20 mm and larger calibers.
20 mm caliber cartridges have an outside bullet diameter and inside barrel diameter of 0.787 inches (20.0 mm). Projectiles or bullets are typically 75 to 127 mm (3–5 in) long. Cartridge cases are typically 75 to 152 mm (3–6 in) long. Many but not all 20 mm rounds have an explosive filling and detonating fuze.
As an example, the 20×102mm has a 100-gram bullet fired at a muzzle velocity of 1,035 m/s (3,396 ft/s). For a simple slug round this is a muzzle energy of 53,567 joules (39,509 ft·lbf).
I looked at faith
I almost walked away
But I looked again
I found the nerve to close my eyes and say the words
To ask you in
And I heard no heavenly choir
No angels in whit attire
i got no amazing super hum omnipresent pow but....
CHORUS
I know You now
I know You now
I know You're in my heart
I know You now
Beyond the shadow of a doubt
I know You now
I look at peace, that once was out of reach
And now it's here
i read Your word that some believe is so absurd
But I hold dear, yea
'Cause You loved me with your dying breath
You saved me when You conquered death