Yesterday I took the Encore pistol in 6.5x55 to the range to shoot some metal targets.  I shot 52 rounds.  The cases are RP they have been loaded once before.  The loads are not hot- they are within the Hornady loading manual limits.  Out of 52 rounds there were 3 split necks.  It seems too much to me.  6% loss seems high, but I wanted to get your thoughts on what is too much.   
Thank you,
Tim