I believe The Newtons last reincarnation (second series - the rights to mfg under the name were held by at least two, maybe three different companies after Newton designed it), the one with the reversed double set triggers, had 30 USG as an option for factory chamber. The 30 Newton would be the other option, but I suppose the propriety 30 Newton was too similar to the 30-06 to sell both options very well.
The .30 Newton has quite a bit more case capacity so it is, performance wise, more like the 300 WIN MAG than the 30-06,
