Yes, a quality barrel fitted correctly to the bolt.
If you already have a rifle, and want to do service rifle/ 3 gun (and are short of funds), you don't need a half to 3/4 moa piece (although it's certainly nice to have). Most people can't hold this standard under the fire and movement stress anyway.
So, I would suggest getting (or upgrading to) quality sights. You can start competing right away. As your ability/comfort level rises go for a better trigger if you want (single stage/double stage, each has it's advantages). I found that practicing with standard/heavier triggers made a big difference when I then switched to a lighter (easier) trigger, as heavier triggers seemed to force me to concentrate more because they were more difficult to work with.
Free float your handguard, then at least you'll know that your sling tension won't be altering your impact points. For three gun competitions, I'm not sure this will make much difference as the ones I've seen were of relatively close range, but for service rifle it's a nice thing to have (if the rules allow it in your jurisdiction).
By now, your skill level (as well as shot count on your barrel) is increased. This would be a good time to have a quality barrel installed. Don't use premium ammo on short range matches--I think it's a waste of $$$$. Premium barrels and ammo for intermediate and long ranges only.
You can get all this work done at once, but saving some of the above expense for practice ammo/time first will ensure that you can develop the ability to take advantage of your premium components. Events like service rifle for example involve
positional shooting (no wussy bipods) so you'll need to work on your positions.
If you want a prone bipod varmint/target piece on the other hand, then it's probably best to get the work done all at once.
Clear as mud?
