Daniel-
Without knowing what type of bullet he was running it's tough to evaluate his comments.
My guess is that he was running gas check cast bullets, sizing them in a lubrisizer die.
What bullet shape, velocity, load, brass etc was this guy running?
Was he trying to get a light bullet to run at high velocity?
Was he trying to get spitzers to cloverleaf at 300 yards?
What else do you know about his load development process that led to the .266?
Folks get all sorts of ideas of how to run a rifle, what the 'perfect load' could be per caliber...
What you've shown us is a cool old classic rifle in relatively original condition. It was built to go out and explore the world and perform consistently everywhere it went, with a specific piece of ammunition -- which was to be available all around the 'British Empire' where it likely enjoyed the bulk of it's glorious chases.
I maintain that you should try what the rifle was built for, the 160gr .264 diameter SNRN jacketed bullet, running your load development over a chronograph, looking for your best velocity at somewhere in the '100 or so FPS slower than period suggested velocity' in your rifle, while paying careful attention to pressure signs along the way.
I'm guessing your rifle will do it's best, and shoot to the sights with the .264" 160gr SNRN Hornady bullet in the ~2200++FPS range. You might even see 'factory spec' velocity out of it, but I wouldn't count on the 'best' load being the hottest, or necessarily the one that gets you the old stated performance.
Those old little 6.5mm rifles earned the reputation of being handy and light, great little game killing machines. The bullet had a lot to do with it.
The 'Factory Ammunition Velocity' claims of the old cartridges was rarely seen when shot through real rifles over real chronographs.
Your rifle was built, shot and sighted, and delivered to run Vintage Period Factory Ammunition - likely Kynoch soft points of similar weight and design to the Hornady.
In conversations with numerous owners of old rifles just like these shown here in the thread, I've heard time and time again that they can be sensitive to powder choice. We don't have the old cordite anymore, but guys the world over keep finding good loads for the 6.5x53r and 6.5x54MS running the 160gr bullet that they were built for.
Give it a try.
Or, give that guy another call and ask him for his load recipe, his bullet mould, lubrisizer, and his sizing die.
That could be the quickest road to success after all...
Still, I'd genuinely like to hear what the bullet design was, and if it was a cast bullet, what alloy he was using and what bullet lube he was running in the lubrisizer.
That 'best bullet for the rifle' in his world might not be the 'best hunting bullet' for that rifle for your world.
--Tinker
