I´m looking into a used Ruger Magnum Rifle in 375 H&H. As far as I know, the earlier version had a very heavy barrel wich was changed after some years of production to a bit slimmer profile.

This particular rifle is made in 1998/1999.
Will it have the new slimmer profile ?

( the seller lives quite a distant from where I live, so no change look it over at this stage )

I'm not sure they ever did lighten the barrels.
They may have.
However, I can say, that, as of right now, they are still a wee bit too heavy for the .375 in the current version.
For the .416 and .458, they are perfect.

I have noted casually over the years (dates approximate) the .416 Rigby Ruger RSM's barrel profile:

First Generation about 1990: 0.810" muzzle diameter, 24" barrel length, sling swivel on a barrel band projecting through the fore-end wood.

Second Generation about 1997: 0.810" muzzle, 24" barrel, and barrel band sling base out on the free barrel in traditional location. This rifle weighed about 10.75 lbs. bare/empty, .416 Rigby.

Third Generation about 2002: 0.750" muzzle diameter, and shortened to 23", traditional barrel band sling base. In .416 Rigby this rifle weighed 9.5 pounds, for the one I weighed.

The .375 H&H's might have the same profile variations, same as the .458's too.

23" barrel length instead of 24" is also a clue to the slimmer barrel, and this includes the threaded portion of the shank for overall barrel length, of course.

CZ made their .375, .416, and .458 all with the same barrel profile, .670" at the muzzle and 25" long.

What I like in sporter profiles, light to heavy depending on the plan:
.375: .625" to .675" muzzle (CZ O.K.)
.416: .675" to .725" muzzle (CZ O.K.)
.458: .700" to .750" muzzle (Ruger O.K.)

The SIGARMS Magnum Mauser 450 Dakota has a 25" barrel with a .670" muzzle diameter, a lot like a CZ .458 WinMag. I suspect they used the same barrel profile on the .375, .416, and 450, but I cannot confirm that.

Thanks for the answers guys.
I will contact the seller and get som more info about the barrel/length/barrelband.
Anyway a good working rifle i guess?
It´s ment to be a present to my son after sucessfully getting his PhD

You were wondering: The RSM's are the absolute best dangerous game rifle made by any high volume manufacturer, in my opinion. For the money, you cannot go wrong. Although they are not a H@H, or Westley Richards, they ARE for the "money", the closest attempt by any "large" American manufacturer at producing a Bond Street quality rifle.
I have a .458lott RSM, and love it so much, I carry it more than any of my higher priced rifles. The Ruger RSM's kind-of grow on you.
Yes, it would be a most fitting present for your son.