Hi mate,
In answer to your question (if i have it right) is that its not so much a case of having one barrel 'looser' or 'tighter' than the other, as such. If you were to look at a springer barrel, and a pcp barrel - both of which, lets say,have a 1 in 12 rifling pitch, this means that a pellet fired out of both would have the same rate of twist. The distances (ie edge to edge, within the barrel) between the lands (raised parts), and the grooves (lowered parts) would obviously be increased with larger calibres, but also bear in mind that each calibre's barrel can also be manufactured so