like tim said..... case sizing difference.
look at one of the spent casings from a previous reload, do you see a line about 1/4'' up from rim ?
your tikka has fire formed the casings to its chamber.
full length size'n dies will only go down so far, and thats the line i'm talk'n bout.
i've experianced it the hard way. bolt gun left-overs are not a healthy diet for the handi's.
thats just my onion----

proly others will chime in....