[Hylander]

I would couterbore with a drill bit.
Or better yet start the counter bore with a drill bit and finish with a bottom cut end mill bit, this will give you a clean flat muzzle, you should only need to
go 1/2" to 3/4" deep.
Remove barreled action from stock, remove bolt.
Clamp the barrel in a bench top drill press hanging over floor or in a full size drill press. Place about a 10" peice of dowel in the chuck down the barrel to get the barrel lined up straight and clamp barrel tight. Now release the dowel from the chuck and lat it fall through the bore. Now place your drill bit in the chuck and drill slow, use plenty of oil. When about 1/4" or so remove drill bit and replace with end mill bit and go 1/2" - 3/4"
To finish off take a short peice of dowel and wrap it with some 0000 steel wool soaked in oil and run it on top of the new muzzle in your couterbore, just a little and very light pressure. Your done.
Done forget to push the reg out the bore from the chamber end and clean.

If accuracy is still not acceptable, rebarrel with a NOS .308 Norwegian barrel and call it a day. Only you will know the barrel is not Israeli