Rick
if your gun is a Chaparral, then yes it's brass plated.
if it's a Uberti, it's gun metal an alloy of Brass simlar to Bronze cannon forgings.
The weak link in the guns Circa 2001-2006-7 was the loading gate tab...Uberti of late don't seem to have the issue.
I had one made in 1978 in 38 cal. I must have put 1500 + rounds through it, sold in 85 and the new owner still uses it
about twice a month in SASS sytle shoots. Lord knows how many he's shot throught it.
OH BTW it's a SR Carbine...
I have a Henry about the same Frame less the loading gate, up until about Feb, of this year it was my main long gun.
many, many rounds fired ( I also have steel frame Henry )
I'm sure they are different in tensil strenght, but your gun metal 66 will serve you just fine.