Remington will be more than happy to sell you a new barrel.
I'm not so sure about that. Because the barrel is sold only as an assembly (or so says my 17 year-old owner's manual) you will likely have to send the rifle back to the factory. (This process may have changed in the interim.)
From all the reading that I have done over the years, I have been told that a carbine barrel is more accurate than a long rifle barrel due to the harmonics.
This is the usual slick magazine over-simplification, and as usual is not true. Rifles used in 1000 yard competition with 30" barrels are just as accurate as those used in 100 yard competiton with 21" barrels. This myth started when some slick writer miss-quoted a benchrest gunsmith who actually said that for the
same weight (which matters in BR as the gun weight is limited) a short barrel can be more accurate than a long barrel. What really matters to all of us is the quality of the barrel and its chambering/installation, not its length.
The quicker the bullet gets out of the barrel the more accurate it could be in theory.
Actually the opposite is probably true. The shorter the barrel the higher the muzzle pressure, which can upset the bullet as it leaves the muzzle. But since 14" handgun barrels can be
extremely accurate it is probably another theory that doesn't work in the real world.
It's not like changing the barrel on a shotgun....
Actually, it is
exactly like changing the barrel on a shotgun, since the M7600 is derived from the M870 shotgun. You can remove the barrel assembly by yourself rather easily with simple tools. The issue would be getting another assembly from the factory so you could do the interchange...
Is changing the barrel worth it? Probably not, as there is a lot of data showing that the velocity difference between an 18" and 22" .30-06 barrel is on the order of 100 fps. I'd not change it unless I:
1 - wanted a different chambering, or
2 - wanted a higher quality barrel to achieve better accuracy.
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