I have four of the old Hamilton 27s and it seems none of them are exactly alike. All, however, have the brass tube for the "inner bbl" and with a steel tubular piece covering the brass.
There are at least two bbl lengths in the group, and one of them has a different shaped forearm....storter and tapered to a smaller thickness. One has a buttplate and the others do not. I am probably wrong, but I would guess that Hamilton made the design changes rather than young owners.
I have several other Hamiltons including the Visible Loader, the model 51 and the model 15.....they facinate me!
I am glad to have found this forum.