Currently wrestling with this exact decision for my next rifle and watching this thread with much interest. I currently have a Tikka CTR 6.5cm in a KRG bravo with a SWFA 3-15 and while I love it, I’ve realized it’s quite heavy for mountain hunting. My next rifle will be a lightweight Tikka specifically for hunting, most likely with an 18” barrel, suppressor, Stockys ROK-stock and an SWFA 3-9. So with all that in mind, I’ll try and summarize what I’ve learned in the process of researching for this build.
I think we can all agree that the 6.5cm and 6cm will both effectively take any game in North America with proper bullets at appropriate distances. This is well demonstrated by the 6mm and 6.5mm threads showing numerous kills with multiple bullets for each.
For me, I think there are 3 main points to wrestle with when considering 6mm vs 6.5mm
1) Difference in recoil and the effect this has on hit rates as well as ability to spot impacts.
2) Maximum effective range based on impact velocity for desired bullet.
3) Availability of factory rifles, factory ammo and if desired, good reloading components.
*Some may also highlight the difference in barrel life, but as I look to shoot more in the future, I’ve changed to an attitude that barrels are consumable and meant to be replaced, so this is not a factor for me.
To point 1: Form and others on this website often highlight the relationship of lower recoil and higher hit-rates. Form recently shared a great scale in another thread (see link below) and reviewed the hit rates associated with them, providing a strong argument that 6.5mm will be more challenging to shoot well than 6mm due to recoil. Adding a suppressor will help with both calibers but the 6mm still wins here.
To point 2: When I use a ballistic calculator with 108 ELD-M for the 6cm and 130 TMK for the 6.5cm with estimated velocities for an 18” barrel I find the 6cm is hitting 1800 FPS around 800 yards and the 6.5cm is hitting 1800 FPS around 650 yards. There are lots of variables that could skew this one way or the other but on average it seems the 6cm will reach minimal impact velocity with these bullets about 150 yards further than the 6.5cm. These distances are further than most (myself included) will likely ever shoot at an animal but it still seems worth mentioning as it is a significant difference.
To point 3: Prior to the new fast twist 1:8” .243 Tikkas, I think most would agree that the 6.5CM was the better factory option if you want to use a Tikka. Now the fast twist .243 has made this less true, though you’ll likely need to reload to take full advantage of the faster twist. If looking at a custom barrel or offerings from brands other than Tikka, then there are a number of other 6mm calibers to consider, the most obvious of which would be the 6cm. For me, I’d prefer to stick with a factory Tikka offering and I do reload, so I’m mostly torn between the new fast twist .243 and the 6.5cm.
Link to post discussing recoil and hit rates for those interested:
Post in thread '16" suppressed elk gun'
https://rokslide.com/forums/threads/16-suppressed-elk-gun.323809/post-3270621