I'm familiar with the 1903 Springfield front-sight 'banded' base, barrel groove, key and cross pin.

IIRC - Some 1903 'banded' bases did not use a key and were held on with just the cross-pin and shallow groove across the top of the barrel (step).

A handy machinist can 'step' a barrel at the muzzle, 'easy-peasy'.

With a close fit, the front-base can be driven on and will stay in place by friction alone.

Some 'J B Weld' coating the inside of the sight 'band' and a shallow notch or countersink on the barrel step would definitely keep the band locked in place.

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