Ever seen one of these?

[barretcreek]

Friend was going through a box of M-16 barrels, all in G.I. wrappers, gauging them. Gauge went all the way in, no resistance. Looks at it, sees it is marked

6-45. Figures it's a contract barrel and just poorly marked. Nope, it is a 6mm barrel, A1 contour with an issue front sight but no handguard metal.

Any ideas?

[Tuna]

6mm TC maybe? The 5.56 case necked up to 6mm.

[DaveL]

6x45 is a legit wildcat caliber. It's a 223 necked up to 6mm with no other changes. I have one myself. It allows you to shot 85 and 90 grain bullets that fit in the mag. Mine is a real tack driver.
HTH
Dave

[lyman]

6x45 is a legit wildcat caliber. It's a 223 necked up to 6mm with no other changes. I have one myself. It allows you to shot 85 and 90 grain bullets that fit in the mag. Mine is a real tack driver.
HTH
Dave

mine also shoots well, and was made by SGW/Oly back in the 80's, (low round count)

not a GI looking FSB on it, and it is marked 6x45 just in front of the sight base

mine is a heavy barrel, or rather what they called a heavy barrel back then, not sure if they offered any other contour then