Re: .243 barrel life question.
Just plan for 2000 rounds of service life. Anything more, you got a winner. Don't waste time on a "setback". From my experience is velocity will slowly decline so, tick more powder here, tick more on OAL length you will be good.
I am still waiting on the Melonite crowd to report in, not just this one barrel or 2.
I don't like to clean, I would only guess that it could help marginally, some like to run the Tubbs coated bullets I hear.
I have shot with and OAL of 2.785 all the way to 2.965 I don't find much difference in the speed I can push a 105gr - 115gr bullet. I found that H4350 or H1000 suits my needs and the OAL I want to run can dictate what powder to use. Other powders work well and can give more velocity but stability is key for me.
I find (with a borescope) that H4350 torches the first 6-8" of the barrel where H1000 will do the same in about 18". I get close to the same lifespan with either.
I had a 5r barreled action that with H4350 looked comical that the lands were basically melted GONE in the first .150" of the chamber. Set the ol' DTAC out to the end of the mag length and back to 1/2-3/4" MOA gun for another 500 ish rounds. I had an AW that the OAL was so short I never thought it would work, still had room for more powder with H4350. And, it still shot at 2990fps.