The "oversize bullet thing" is greatly overemphasized. Old P. O. Ackley did a pressure gun test of grossly oversize bullets. He started with a barrel chamber for what he called "the .270 magnum". He fired a load with the 150 grain bullets and recorder pressures. He then rechambered the same barrel and fired 150 grain 7mm bullets down the .270 bore with the same powder charge and recorded the same pressures. He then went to .308, .311, .323 and finally up to .358" 150 grain bullets, rechambering the same .270 barrel over and over. His conclusion was that so long as the chamber neck and throat are large enough to allow the neck to expand, oversize bullets make no difference in pressure at all. I'd have it rechambered with a proper 8x57 reamer and shoot factory loads or comparable handloads with no fear. As is, I'd be concerned that the neck may be pinched in on a .323" bullet and that WILL raise pressure, perhaps disastrously, even with light loads. Perhaps a chamber cast will tell.
