Having a heck of a time getting an accurate load for the 6.5x55 Tikka. The loads for my M96 just isn't as good in the Tikka. Been using WW brass, Fed 210, RL22, or H4831SC, Hornady 140gr AMAX and 140 gr Hornady Interlocs. The best groups are right around 1". The rifles been bedded etc. Pretty sure it should do better.

When I could still get it, I used a max charge of H450 in my 6.5x55 Tikka and it would print one hole/100 yds. all day. So far, I haven't found any other powder that will do as well.

What bullet weight did you use, 120 or 140?

I've used 47gr. IMR4350 and 120gr. bullets.

You could try Varget and 210match primers. This combo worked great in my old 260rem witch is pretty much the same as the 6.5X55.
Tikka makes a great gun and is known to shoot well. The 140Hornady A-Max should do real well at 300yd and beyond. Have you had any problem with over all lingth and fitting the rounds into the clip?

CainR, Sorry I didn't get back sooner. I was using Sierra 120gr. match bullets. I was getting about 2950fps clocked and, no kidding, one hole @ 100yds. Believe it or not, I got good results, as far as accuracy, with Federal Classic 140gr. crap as well! The 6.5x55 seems to like the slower stuff. Damn I wish I could get more H450!