Raimey,
I resize .264" bullets to .261" and .321-323" to .318" but this amounts to .005" reduction or less. It has been reported that reducing a normal "cup and core" bullet more than that can cause the core to loosen in the jacket. This is because the reduced jacket may "spring back" some, while the lead core won't. On the other hand, I have .228 bullets that a friend "bumped" up from .224" for use in the 5.6x61R vom Hofe. The difference between .243" (6mm bullet) and .228" is .015" reduction and 3 times the limit I have been using for resizing jacketed bullets. I don't know of a .233" (within .005" difference of .228") bullet I could resize to .228". On the other hand, the "bumping up" process my friend uses is not limited to .005" like resizing is, because the core is expanded against the jacket instead of the jacket being reduced against the core. Indeed, expanding the core against the jacket is the process used in making new bullets and is used without problem. Another acquaintance tried turning .243" monometal bullets to .228" but these resulted in high pressure problems and could have resulted in a damaged rifle. His basic idea is worth exploring, I believe, if grooves are added to reduce the pressure required to force the monometal bullet through the lands in the barrel. Some commercial manufacturers use this idea in their production of monometal bullets. I noted that number 1 wire gauge copper wire is nominally 0.228", but even though I have turrets for a couple lathes, given my age there is not enough time left to work out production details.
Mike