Thats the beauty of running below the sound barrier. As long as your velocity's std dev or spread is low (like 5-10fps) there is no limit of effective range until the bullet runs out of steam. Using a 240gr matchking with a bullistic Coef of over .6 starting out at 1086fps, you only go down to 900fps at 400 yards. Thats whats so great about high BC.

Your limit most likely will be your scope elevation adjustment. With 100 yard zero, you would have to raise elevation 50MOA to hit at 400 yards. Most target scopes run out of elevation adjustment at 56MOA. Thats using a 30MOA base.