Yeah ... that would have been metal.

The sidelocks look to still show some case hardening.

The only thing that I could find was this .. for the "f" denotation ... Three different Quality/Grade F shotgun barrel steels were used, (damascus, Best English Stub Twist, and Royal fluid steel). Are the barrels twisted steel?

That means, don't fire any modern smokeless stuff through 'em.

Are you certain that the date of manufacture is 1920? If so, there should also be the demarcation of "Hunter Arms".

I'm gittin' all confused, as the switch to "Nitro Steel' commenced in the eighteen nineties.