"Would this be the same as saying that the case is to big in reference to the caliber size?
"Does this have an adverce affect on accuracy? If so, Why?
"What I'm having trouble with is this...
"Many post here and on other sites say that the 6.5 WSM is overbored. If a 140 AMAX say at 3000 fps shoots accurately from a 6.5WSM and shoots equally well from a 6.5/284 though powder weights vary, and the WSM case has leftover room what does it matter? Why is the 6.5/284 more accurate according to many, a fact that I'm not disputing because I don't own either. In this example, is this one of those "inherently accurate" rule or is it really the case of the WSM being over bored?"
MAELTY
Yes, among other things "overbore" means that the ratio of the case to the caliber is too big to maximize efficency.
Accuracy depends on so many variables it is difficult to say if overbore is a factor. As Mikecr notes, the short range benchrest guys seem to maximize accuracy with small cases launching 6mms. However, both one mile and 1000 yard benchrest accuracy records seem to be set with overbore cases.
It is notable that the .243 Win, which is overbore seems to be inherently more accurate than the .308 Win -- same case different caliber. In terms of the 6.5, I have lots of experience with the 264 Winmag, the 6.5/06 the 6.5/284 Norma and the 6.5x55 Swede. All except the 6.5 Swede are overbore at different levels with the 264 Winmag being the most overbore. All are accurate in my experience with the 6.5/284 being the top performer both at 100 and 1000. The 6.5 WSM or its variants may be as accurate as the 6.5/284 but I doubt that the former is as efficient as the latter in terms of barrel life. The most accurate 100 yard rifle I've ever owned was a 220 swift which held five in 1/4 inch after the throat was almost completely eroded by 2,000 plus rounds. That said, the cone of dispersion did not hold accuracy much beyond 300 and at 500 it patterned like birdshot.
There are alot of super overbore rounds out there but most of them are marketing gimmicks in my opinion.
[ 10-14-2004: Message edited by: Crispin ]
[ 10-14-2004: Message edited by: Crispin ]
[ 10-14-2004: Message edited by: Crispin ]