Rockdoc,
I know of a Poli Anson Extra 2 barrel set in 24 and 32 gauges. Poli built the gun on a 20 gauge frame because of the firing pin hole spacing.
The 32 gauge barrels are widely spaced to line up the primers with the firing pin holes.
I guess if you had a 28 gauge that was originally based on a 20 gauge frame (and there are a lot of them), then over boring a 28 to 24 should work fine.
Another friend had Kirk Merrington work on his 24 chambers to correct a headspace problem. Kirk has the chamber reamers and should be able to do the conversion.
Joe
