See post by Luckus....

He knows

I neck size all used brass until it won't chamber up comfortably. Then, I full length size them & the process starts all over again.
The nice thing about neck sizing is you can get more use out of your brass.

Bullet length seating can make considerable differences in your accuracy. Try .005" at a time. Just remember where you started just in case.....

For something as simple as COAL, it's amazing the difference a few thousandths in length can make.

Frank in Fla