Had a 264 (can you say over-bore). When bbl got hot, I let it cool. We did not believe in much cleaning back then (1960's) but started cleaning regularly in 90's. Always got decent accuracy of an inch or so at 100 with handloaded ammo. Shot plenty enough for sighting-in and hunting including some ground squirrels. Heard all the "less than 1000 shots" stories but really didn't care. So, I can't imagine that 6.5-284 would be much different unless you shoot a lot or heat it up too much/often.
I’ve read it’s not overbore if you can find slow enough powder.
Even the 26 Nosler, with Vulcan cannon powders, may qualify as not being overbore.
That may take some selling.
DF
