I have the .270 in 24 SST.
I had a devil of a time with the shots stringing high in a cold barrel. The first rounds were about 4 inches high at 100 yards. They grouped lower after the 3rd shot or so very nicely. After much cursing and belly aching, I ran about 80 rounds through it, cleaning often. Then I fired 5 rounds and left it dirty. I let the rifle rest for two days. Tried again from a dirty, cold barrel and now the sucker now shoots 3/4 inch groups without stringing as the barrel heats. Federal Premium 130 gr shot best and I tried all the "high dollar" stuff.
Lesson learned for this gun. Fire enough to break it and clean it good while breaking it in. After that, fire 10 rounds the day before season and then hunt with a dirty barrelfor that week.