My father in law has a real itch for a stainless 6mm Remington.  I was telling him that all he had to do was run a 6mm reamer in a stainless 243 and he'd be good to go.  

Is it really that easy?  I don't have my reloading manuals with me (not at home) so i was unable to check the rim size.  If I'm not mistaken they are the same, and the 6mm is a slightly longer round with a sharper neck.  

What do yall think?  Jim

You're right about the head size.  The only possible problem w/the conversion would be to make sure the magazine length is sufficient to handle the longer 6mm round.  If that's no problem, get the piece to a 'smith with a 6mm chambering reamer and go for it.

I doubt a 'Smith will want to touch this job.
There's too great a chance that the reamer will not bore straight due to the size of the 243 chamber already there. If he "needs" a new rig (Totally understandable) I'd steer him to a 243 Ackley. I assume he has a 24 or greater length barrel otherwise the gain would be negligable.
I had a 243 ackley for a while built on a long action with an 8" twist 28" barrel.

I didn't think about the difficulty associated with using a reamer that is so close in size to the current caliber.  

At least logistically the conversion will work.

I know there are many better calibers but he loves his 6mm.  I think it was one of the first calibers he hunted deer with.  He was wanted to get an action and rebarrel it, I was just trying to find a less expensive alternative for him.  Jim

I'd call a couple gunsmiths and ask if they have a 6mm take-off.
Try www.varminthunters.com as well.
If I had one it would be his for postage.
I'm sure he could find a even swap as the 243 brass and ammo are more plentiful.
Spending even more of his hard earned:
There's a resurgence in interest in the 6mm Rem. reamed short to use 22-250 brass.