A good .243 bullet, one that weighs between 85 and 100 grs can be counted on to expand to .45 caliber, and will probably penetrate a foot or slightly more. As such it will easily kill a deer, but switch to a cup and core bullet, and I am of the opinion that the .243 tops out at 100 pound game. A .30/30 doesn't need as good a bullet to perform well due to its slower impact velocity. While 170 gr is the most common, 125s, 130s, and 150 have proven to be viable choices in applications where pointed bullets can be used, and cast bullets from 180-200 grs are not unheard of. If the .30/30 slug expands, it will likely end up between .45 and .60 caliber depending on the choice of bullet and the range at impact. The less the bullet expands, the deeper it will penetrate; but given a .60 caliber frontal diameter, the .30/30 bullet will typically make a foot of penetration. IMHO, if the bullet can't be counted on to penetrate more than a foot, a 200 pound game animal is about its limit. Clearly a 6mm bullet won't do the larger game any good, but in this business of cartridge choice for big game, why is it necessary or even reasonable to choose the lowest common denominator? Despite my opinion, a million moose have been done in with .30/30s; but could that comes down to a lack of options rather than the .30/30 being the ideal moose cartridge? But Sheep's comparison between a 6.5 and the 6mm is curious, considering a typical moderate capacity 6.5 bullet weighs 25% more, expands 20% larger, and penetrates 30% deeper.