D.Camilleri,
Please understand that I in no way want to undermine your smiths comment to you but I have to respectfully disagree with quite a bit of what you have been told.
I will start at the top.
First off, Rem will do nothing if you just send them the barrel. They require that the entire rifle be sent back and then they will decide what to do. Generally, they will not contact youeither way, if they warrantee or charge for replace so your kind of at their will.
Personally, as an extreme accuraacy gunsmith, I love Rem rifles but this is only because I am looking at the action as the componant I want to use in my rifles.
27" is a great length for this round if you will be in relatively open country which is what this round is designed for. No point taking a 338 RUM into the dark timber after elk.
That would be like taking a NASCAR down a gravel road.
With a brake installed a 27" barrel makes for a long rifle, not overly long in my book but some do not like the length.
Also, do yourself a favor and get a barrel with a muzzle diameter in the .700" range. At 27", in a round like this that can drive long bullets to high speeds, the added weight will help with the rigidity of the barrel and greatly increase accuracy over a #3 or #4 contour which is generally used on these rifles.
YOu will be looking at around another 1/2 lb of weight but the accuracy benefits are well worth it.
This is a big case, the 225 gr bullets are a VERY good balance of velocity and penetration for North American game, even the big stuff like elk and moose.
If I were hunting Alaska for the big bears(browns, Polar or Grizzlies) go up to a 250 gr premium bullet but for everything else the 225 is a much better choice in my mind.
I have several customers using the 225 gr Nosler Accubond with very impressive results.
As far as this bullet weight saving on throat life, well, it has more to do with heat, pressure and time then it does with bullet weight and velocity.
Generally the lighter bullets use heavier charges of faster burning powders then the heavy bullets,
But then the heavier bullets use much slower burning powders which hold the temp higher in the bore for a longer period of time.
In the end, it is really a wash as to which will erode the throat faster if both are loaded to correct pressures.
IF you rebarrel with a custom barrel, make sure your throat is cut at no mor ethen 0.0005" over bullet diameter, this tight throat will save on your throat as much as anything because it greatly reduces the gas blow-by that acts as a blow torch on your throat.
Just ask your smith for the dimensions of the throat on his reamer and if it is SAAMI spec, ask him to get a better dimensioned reamer.
As for the 300 RUM, I had one of the very first Rem 700's that came to Montana and have put well over 1500 rounds through the barrel.
After accuraizing the rifle it would hold three shots in the 1/2 to 5/8 moa range in the beginning.
Now, the throat is severly eroded, in fact, I will be rebarreling the rifle here soon but all I have to do is seat the bullets out a little more to chase the erodong rifling and I still get 3/4 moa grouping.
I will say that I have lost around 50-75 fps compared to the beginning but it still has more power then needed.
I also load this rifle full tilt, 3400 fps with the 180 gr partitions.
Throat erosion is a funny thing, in a big game rifle, it rarely means the barrel is ready for retirement, especially if your a handloader.
It is generally a sales pitch that gunsmiths use to get a rebarreling job instead of getting all the useful big game hunting life accuracy out of a barrel.
The difference you will see rechambering to a custom barrel has more to do with the barrel and custom throat then it does with the old barrel.
Good Shooting!!
Kirby Allen(50)
