Anyone know what the minimum outside diameter might be?

I have a 1917 that has had it's original barrel cut to 18.5", and being a handy little bugger, but me also having a surplus of 30-06's, I've had the idea of reboring it to a 9.3x62 or possibly a 400 Whelen.

I am not positive, but I believe the barrel was turned down somewhat to mimic a sporter contour, as the barrel seems thinner at the muzzle than a standard issue 1917 barrel would be at that distance from the muzzle.

It's sure not a pencil barrel...just not sure if it's got enough "meat" to allow a rebore.

If not, it can stay a 30-06 happily enough. Just figured my pre64 M70 in 30-06 has that cartridge covered. No need for two.

I would say about .615" with a Stainless barrel and .600" with a CM barrel would be about as thin as you would want.

.600 would be about perfect. I have a .375 that mics at .615. It is an absolute dream to carry and shoot.

Muzzle diameter guidelines:

Lightweight sporter = bore dia. + .250"
Medium sporter = bore dia. + .300"

Less than .250 ( meaning a wall thickness of .125 ) can be fussy

Minimum would be .566". This, on carbon steel, per Cliff LaBounty when he was doing my rebores.

I just measured it at the muzzle, which from a glance appears to be the thinnest point, and it is 0.602".

Sounds like there maybe some room to do something....but it may not be the easiest rifle to get shooting well?

Shooting well on skinny barrels can leade to brain damage.

JES Reboring recommends at least .200 over bore diameter. Sounds like you have room for a 9.3 or 375. A 400 Whelen would require a .611 diameter muzzle.

The Zastava factory barrels on the 9.3x62 rifles are very thin at the muzzle...

That is 14mm or .551" for the metrically challenged.

I have tried to blow up guns. They are hard to blow up with walls .1" thick.

The way hoop stress works is that it is proportional to inside diameter times pressure divided by wall thickness.

So the higher the pressure, the thicker the walls need to be.
So the larger the inside diameter, the thicker the walls need to be.

In general, rifles have wall thickness 5 or 10 times thicker than needed for pressure.
Handguns are sometimes right on the edge.
You may have a 357 mag with 0.050" chamber wall.

The reason we have thick walls in rifles is to make them heavy.

Some will tell you we need thick for stiffness, but skinny barrels well bedded to super heavy stocks are fairly accurate.