I think Varget is the best allround powder in .308. My Remington M40 just loves it as did my PSS. 44grs is about perfect. In my M1A I like 45grs of R15 with the Sierra 175 Match King, super accurate. I found that at least in recent lots of the two powders that R15 is much slower burning than Varget at least in one application even though burn rate charts have them usually side by side. Varget has become the powder of choice in my Win 1895 .405 Win. Similar doses of R15 ran 150fps slower which really surprised me. But I do own a chronograph and have since the mid 1980's. Your Tikka should be 22 inches no? But remember also there is such a thing as "fast" barrels and "slow" barrels. I had a Douglas barreled .280 Rem that my friends improved version could not equal in speed. Burned the hell out of him!