Just right offhand, I can't immediately recall any round that has a bullet diameter greater than the case diameter....
Very funny. I meant to type “greatly less than” or “significantly less than”.
You're thinking of the idea that such a design, frequently including a taper to the overall case dimension, is more easily guided into the chamber during the feeding cycle. But that may work against reliable feeding within the magazine body, [or belt link] in that the space between rounds offers a place for dust/sand/mud to collect and de-lubricate the cartridges during the feed cycle. I'm waiting to see how a pal's .450 Hornady [.450 Bushmaster, .450 Thumper]conversion for his M4 works out, but the reduction of magazine capacity is not exactly what I'm after.
