Lots of interesting error in the above posts, which I'm going to leave in place and shoot all down with this one.
The springback you are getting is real. Part of it is the bullet and part is from the dies expanding as the bullet is pushed in and brought back out. In other words. If you had the die out where you could measure it, pushed one of your hard bullets in, and measured the die, you'd find the dies outside diameter would be approximately the same amount larger as your bullets are oversize.
Ever hear of Newtons law? For every action there is an equal and opposite reaction. -- If a fly lights on a railroad track, the track will bend down where he is setting, an amount relitive to his weight vs the rail road tracks strength. When you drive your rig down a super expressway, the road sags under your rig then comes back up behind you. Ditto when you walk across a concrete floor of any thickness, or a wood floor. The amount of sag in any of those cases is easily measured with high precision instruments. Few machinest have a clue of how important this fact is to their livehood and skill, but it counted high to me during the 25 years which I rebuilt high precision metal working machinery. When I was working to real close tolerances, I had to wait for up to a half hour after handling metal for the hand temperature to stabalize so any warp would come out of the part before taking measurements.
Newtons law applies to your bullets and dies, your reolading press frame, and your firearms, which stretch and bulge every time you drop the hammer. The cylinders in your auto engine bulge and shrink back with every ignition of the gas, even if you are punching it up to 100 MPH.
Lino comes to full hardness quite a bit quicker than quenched WW alloy, with both reaching about the same hardness in their appropriate times. With either though, when you have this problem, cast for only about an hour at a time. If you are quenching to improve hardness, pull your bullets from the water immediately, dry them well and size while they are soft. While soft, bullet diameter will be very close to ACTUAL sizer diameter, which certainly isn't as stamped on many dies..
I have have measured this spirng back thing going well over .002 thousandsth of an inch. It will be worse with large diameter bullets, whcih mean the sizer die walls are thinner and weaker, and less with smaller diameter bullets which leave a thicker sizer die wall. The most severe springback I've had is with heat treated high speed babbit metal which reached a hardness of close to 40 bhn, and would CLEANLY penetrate 1/2 inch steel out at 100 yards when shot from a 30-06 at full power, by the way.
