You make a good point. Increased case capacity is useless behind bullets too skinny to transfer the powder's energy efficiently. "Overbore" is as relative a term as "liberal" or "dangerous." All bullets make barrels cringe. Heat and friction eat steel. Big bullets throttled by modest charges of powder, as in, say, a .35 Remington, are easier on bores than smaller bullets driven faster. But shorter barrel life is a price willingly borne by shooters who want to hit at 1,000 yards. An automobile that gets 30 mpg is efficient, but it won't win at Daytona. The 6.5/284 is justly popular among long-range target shooters, as it can drive wind-cheating bullets flat enough for X-ring hits out yonder. I've used it on elk. The rebated case doesn't thrill me, but ballistically it's a .270 Winchester, and thus a worthy big game round. Irrationally, I also like the .264 Winchester Magnum, perhaps because it's been so roundly (and undeservedly) criticized and has responded beautifully to my handloading. If you like speed and reach, the full-length-magnum .26s shine. But they're the very definition of "overbore." Rate of throat erosion in barrels, by the way, depends on how fast you follow one shot with another (accrued heat) and the powder type and charge, as well as bullet diameter, type and bearing surface. .... WvZ
If the 6.5-284 Norma is "overbore", and potentially a 1000 rd. "barrel burner", what would we consider a 26 Nosler or a 6.5/300 Weatherby? I understand the utility of the "overbore" 7mm's for hunting but not the 6.5's. A 28 Nosler, 7mm Dakota, 7mmRUM, etc. can send a 180gn plus VLD bullet a 1000 yards with enough energy to reliably kill an elk. Just because a 140gn 6.5mm gets there at the same speed is it anywhere near as terminally effective? I am guessing that the "super overbore" 6.5's are the flattest shooting long range cartridges, but what niche do they fill?
I greatly enjoyed the article. It is a real treat to have detailed articles written by Wayne and John on this site.
