Yea a 10 twist will stabilize the 240 SMK until around the 1500 yard mark as Bill Baily reported here on LRH.
The higher twist barrels do not affect BC and according to Brain Litz (Berger Ballistician) the only advers affect tp overstabilization is extra spin drift, nothing more. I agree with Brian
Here is Brain's post on Snioers Hide
Bryan Litz
Sergeant
Registered: 24-08-2008
Posts: 90
Loc: Ohio Ratbert,
Thanks for your comments. Fortunately we're all on the same page at Berger as far as doing what it takes to enhance the shooting experience, regardless of brand.
DB,
Actually the window of proper stability is quite large. On the low end, you have to use at least the minimum recommended twist. On the high end, well, most of the adverse affects cited for over stability are myths. The most adverse effect of very high stability levels is extra spin drift. Other than that, elevation is not affected and BC is not affected.
I think most of the myths about over stability stem from imperfect understanding of the sights including: imperfect zero, click adjustments not being true, canted reticle, etc.
I occasionally see cases of extremely high (and low) BC's being reported by those conducting tests. You'll find that in most of those cases, the non-physical results are caused by oversights in the test.
It's a comfort to know that most of the smoke and mirrors surrounding BC is just that; smoke and mirrors. At the end of the day, actual BC's are very well behaved and constant from all rifles across a large range of stability levels. If two bullets have the same shape and one is heavier, the heavier one has a higher BC. If two bullets are the same weight, and one is more streamlined, the more streamlined one has a higher BC. This is common sense but many 'advertised' numbers contradict these basic trends and it causes unnecessary confusion.
Take care and good shooting,
-Bryan
_________________________
Ballistician
Berger Bullets
Testing for ballistic coefficients - Sniper's Hide Forums