It is good to see people that make barrels advise against fluting after the barrel is installed because
it is a crap shoot and very hard to predict the outcome .
The best smith in the world cannot guarantee 100% success every time because he has no control
over the effects of stress left in the barrel after final stress relieving. The barrel maker has quality
standards that he has to meet and if the barrel does not meet them after he is completely through
it is rejected and does not end up on someone's rifle.
You can get away with it most of the time but not 100% of the time so that is the reason it is
not recommended. Besides, you can save more weight by changing scopes and bases if weight is an issue.