I do the same as tinker,,straight into the 6.5 M/S sizer then trim them. I use some HXP 303 brass and with that I have to inside neck ream,,I use a drill for that. It's a common letter or number size,,don't recall which it is now. I just keep one in the die box for that purpose. Sounds crude but I see no difference at the range. It just removes a slight ledge at the bottom of the neck inside where it meets the shoulder on a freshly formed HXP military case.
Commercial 303 or 30-40Krag brass seems not to need any inside neck reaming,,at least none that I've used so far.

Don't be skimpy on the case lube when you do the sizing operation, just avoid excess on the neck so you don't end up with dents in the newly formed 6.5 neck.

Neck size only after the first firing. They last quite a while for me, but I use minimum or near min loads anyway.

I've had good luck using 220 Swift brass.
Not that 220Swift is all that common but you never know who has what lying around.
I was fortunate to have a 100 or so cases given to me.
Expands easily in one step, definetly easier to do than the 303 neck down process. The slight semi-rim of the 220 works in my rifle as well as the full rimmed variety case. Might not work in others though.
They make good 6.5 M/S cases if you turn the rim down.