I shoot a .6mm Rem. in a Steyr Model L and it will nock a deer down with the best of them !

This gun was given to me and I actually had never heard of the caliber before........so I did a little research ! I basically found out what Jagmagman said......the .6mm came out first and is a necked down .257 Roberts shooting a .6mm bullet ! The first rifles were not very accurate over 100 yrds due to the twist rate ! Win. came out with the .243 which I believe is a necked down .308 and had a better twist rate and was a lot more accurate ! So the .243 jumped out way ahead and by the time the .6mm guns twist rate was changed ........they were left in the dust !

The .6mm has a little better ballistics and I can vouch for their nockdown capabilities ! But also I can vouch for the fact that ammo is much more limited and harder to find ! And it has a longer action.......if that bothers you !

Personally .......if I was buying new......I like the 25-06 better than both !! It is just as flat shooting......has a little more energy and range .........and plenty of ammo variety and availablity !! Good luck !!