Can a Greek model 03/14 be re-barreled to 6.5x55 Swede without having major issues in regards to feeding from the rotary magazine?

Just no, 6,5x55 has so much bigger case that yours magazine will need quite a lot alternations i.e. rotary magazine is very sensitive of case dimensions.

My question is why? The 6.5x54 MS will from a practical standpoint do anything a 6.5x55 will. 6.5x54 brass, ammo, and reloading dies, while not as common as 6.5x55, are still easy to come by.

Yes, both the above posters are right; these mags are tricky and even getting them to feed with regular .473 head ammo is touchy. If you can, best to keep it in 6.5 MS.

The simple answer is NO!

If you read Ken Waters' Pet Load article on the 6.5X54MS you will get some useful info.

The simple basic issue is the magazine well & spindle. These rifles were hand made and a true craftsman's creation. Each rifle was scaled to the cartridge. The magazine spindle was made to hold the 160 gr RN bullet. You will get a real understanding of it if you take off the spindle and place any other case into the 5 grooves. The radius and taper will only fit the cartridge that the rifle is chambered for.

My 9.5 does not like the Sierra spire point bullets & I have to be very careful in seating the bullet if it has to work in the magazine.

The top round in the magazine also sits IN LINE with the chamber & not staggered like a Mauser M98.

You will need a NEW spindle that EXACTLY fits the new chamber / cartridge. Or the round will not feed correctly & the magazine will either jam or spew out the rounds.

Then you have the magazine well which is also made for each caliber. You might get away with a 260 Rem in the well as it is smaller than the 6.5X55 Swed. I have seen a rifle rebarreled to a 243 Win and the magazine crudely modified with a couple of steel prongs welded on to keep the rounds in the mag. Not the usual smooth feed but it worked. An ugly rifle though - lots of butchering to fit the 243 barrel to a 6.5 full stock!

My 6.5MS & 9.5MS rifles look very much alike at first glance except the obvious barrel size. But closer inspection shows a lot of subtle differences in the whole rifle. They were NOT made with a single drawing or template!

I had to measure my 9.5 in minute detail and put it on Auto CAD before I got the stock partially inletted on a CNC machine. Yes - the full barreled action.

The 1950s MCA models were different in that they were made for more high pressure rounds including the 6.5 Swed.

What Naki said.

My greek 6.5MS won't feed anything but 160rn. The barrel feed ramp is used to pop the round out of the magazine. If I load spire points the shoulder will get crushed in the magazine.

Back in the old days, McGowan barrels would re barrel your 6.5 X 54 MS to .224 X 54 or 6MM X 54 or .257 X 54 MS. Loading dies were available for the same. I don't know how much business he got in those wildcats but I always thought it was an interesting solution to the MS feeding issues.

Thanks to everyone for the responses it looks like this project will be chambered in 6.5x54 Mannlicher.

First, let me say I would leave it as a 6.5x54 MS.
I have converted a Greek MS to 7x57. It feeds just fine and the release button works and releases the rounds for unloading.
It's necessary to open up the rotor for the slightly larger case. Took hours and hours with a sized mandrel and various grit wet and dry paper to get the 7x57 rounds to fit properly. The shoulder was not actually a problem. Neck was done separately.
The other necessary work was on the well area. The flat surface that the rounds ride up against needs to be relieved. More hours and hours draw filing and polishing.
Why did I do it. Had a .284 barrel, reamer, pitted action that was given to me and lots of time.

Remember the original rifles often had .268 inch bore and all modern bores are .264. Lothar Walther will do an original profile barrel but the bore is .264.

Mir rifle is .268 & I use the Hornady Carcano bullets in 160 gr RN. They are more accurate.