I would suspect that .001" difference has little to do with your issue. The original 7mm round that these were designed for was for a long heavy bullet with a rifling twist that was tailored for it. Modern 7x57 uses a lighter bullet with a different twist.
If you want to do a .285 bullet, casting would be the most logical step; but a long heavy bullet would still be necessary.
Another methodology is called "bumping up" the bullet diameter, here's a discussion: http://www.lasc.us/Brennan_4-1_BulletSizingBumping.htm
While bumping up is mainly for cast bullets, bullet swage dies from Corbin or CH4D should be sources, you would have to pay for a specialty die diameter and the jacket would tend to spring back, meaning that the die diameter would need to be bigger than .285".
HTH
Wiley