Sounds like a good idea. I hope the build goes well and would like to see some pics. Good luck!
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I would recommend against fluting it for a couple of reasons. First, fluting is best done by the barrel maker during the barrel making process and next, it will decrease the stiffness of your barrel which is probably a #3 or #2 countour from the factory. Just my $.02
To be honest, having an ultra light rig and having a dedicated long range rig are two different rifles. I am not a gunsmith, but I would be leery of having fluting cut in a featherweight rifle barrel if you want the ultimate accuracy. I too have a 300wsm Tikka w/ a 23.75" barrel and a plastic stock. The rifle weighs just over 6lbs w/o scope and I wouldn't want the rifle any lighter because then I may need a Muzzle brake. You may wish to ask a question about fluting affecting the accuracy of the barrel on the Gunsmithing forum. Guys like JE custom, 50 driver and other gunsmiths or dedicated lrh'ers will give you good advice.
I shoot 180 gr NAB's and H 4350, CCI BR2's and Win brass with the shoulders bumped and bullets seated to fit the magazine. It shoots .75 MOA out to 500 pretty consistantly and many are in the .5 MOA. As good as I could hope for from a Factory rifle with a lightweight barrel. I don't advertize the powder charge but I am able to get 2945 fps and it does flatten primers a little.
I used to re-load but now I "hand-load".
-- Well, at least I try --
So far, everyone has parroted what I would have suggested too. Having a barrel fluted after the fact is not a good idea. Too many variables, none of which are condusive to accuracy. Also, the fluting buys you very little in weight savings.
The single best thing you can do to reduce the weight is change your stock. My suggestion is to look at the Bell & Carlson "Medalist" stock (full aluminum bedding block) which is very lightweight and reasonably priced. For additional weight savings, you can look at the McMillan stocks, any one of which can be produced in their "Edge" technology which produces a stock that weighs in at about 23-24 oz. The McMillans cost considerably more than the B&C (probably in the $600 range in the "Edge" version) and will take about 5 months to get, but you would have the ultimate, light weight stock. And probably have no more tied up in it as you would paying a smithy to do the barrel work you were considering anyway.
Bottom line is don't mess with the barrel. Save weight in your stock selection.
Something else to keep in mind, significant reductions in weight mean increase in felt recoil and the balance of the rifle is affected. There is such a thing as "too light". Just things to consider along the way.
Again, I am so pleased with the respose to my question and the imput that you all have made. I am having the barrel ported and the trigger honed on Tuesday. Our buyers are going to the show durring the first week of February and will be keeping an eye out for a quality stock to use. I have purchased some Barnes 180 triple shock and Nosler AccuBond 180 to load to start with. I have ordered some 168 Berger and Barnes 168 to see how the rifle likes them. As this developes I will try to share the steps along the way. I belive I can have a pretty good shooter with all your help and imput. I have a load that shot one hole for a friend in his Tika and I will be trying it in the rifle first off. Thanks again.... Dave