i'm watching this topic with interest . thinking of a 6mm for precision range work with occasional hunting uses. i prefer my 308 tikka as a all rounder out bush, but the 6mm has merits for target work , goats and the majority of pigs that i encounter. tikka make a 8 twist 243 now . with regards to dies i prefer decent quality hornady, RCBS or redding . i've used lee dies with no issues , but you get what you pay for quality wise . having said that i had a set of hornady 222 dies that tried to put a belted rim on my 222 brass . bought a set of rcbs dies problem solved . cartridge choice wise i'm on the fence between 243 vs 6mm man-bun . 243 has the runs on the board , but being OCD i can't fathom the short neck and shoulder angle that blow torches the barrel throat . the original warren page 240 super pooper used the long neck and shoulder angle of the 257 rob/6mm rem , which is close to the man-bun case neck and shoulder, creedmoor case is also a twin to the old 250 savage ackley case invented waaay back when . the wheel has been reinvented quite a few times now

winchester chose to stick with the shallow shoulder for ease of brass manufacture and smoother feeding with their 243 case. in a tikka t3 feeding would not be a issue with a single stack mag . am i overthinking the case differences , yes i am . i did mention i'm OCD ...

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30-06 guys once derided the 308 as some reinvented, new fangled upstart

, the 6mm man-bun is gaining ground in the USA for specific long range comps , particularly in AR platforms . we'll have to see if it takes hold in OZ, but i'm sceptical as the 243 has been doing sterling service for a long time now . component availability and ammo in the regions is a no-brainer in favour of the 243 , but the big C have stocks of hornady 6mm man-bun ammo, and cases aren't too hard to find in bigger gun shops .
i think twist rates are specific to application , 1-8 in 243 would suit you well wapiti for your intended uses/bullet weights . freebore chamber length might be a issue with case capacity and longer projectiles with a standard 243 chamber. from what i've seen and heard with 243's the 87 vmax is a really great projectile for general use and accuracy , which only requires a 10 twist . i've been told 90gn nosler bt's and 95gn sst's are good for deer and pigs , but i think this is starting to push the boundaries of the 243 in comparison to 308's . having said that , there was a fella on here years ago up in FNQ that only had a 243 and used it on everything up to scrub bulls with head shots . one of you other long time forum members might remember who that was. "daddy bang" i think ? loved 243's as a extremely accurate mild recoiling rifle that did every job he asked of it .
JMHO opinions , from my limited experience , perspective and intended uses

time for another coffee .....