Welcome to the Voodoo of reloading where changing one single component can drive you nuts. In this case, the internal ballistics of your combination translates to poor accuracy no matter what OAL length you try. Just note that this bullet style and brand is no good in your particular weapon and move along. Simply changing to another manufacturers bullet of the same style could change your groups dramatically. If you have a bunch of these projectiles, relegate them to plinking, tin can, rapid fire, burning through the ammo loads. Sometimes you get the same kind of results with premium bullets or one type of primer in a particular weapon.
I learned my lesson with a M96 Swede. It shoots like a dream when you feed it something it likes. It patterns worse than a spreader choke shotgun when you feed it something it doesn't like; there isn't much middle ground either.