Re: Bushing Size?
[ QUOTE ]
Then came the final, critical step — the step requiring a sensitive touch and #400 sandpaper — the “tuning” step. “The secret,” Virgil said, “is to get the neck tension — the grip of the brass on the bullet — exactly the same on every case. You do this by firing the case and then feeling the bullet slide in the case neck as you seat it. Here, a micrometer won’t do you any good. Feel is the whole thing. If any case grips the bullet harder than the others, you take three turns over the sandpaper and fire it again, until you get exactly the same amount of seating pressure. Until the necks were tuned, I didn’t feel I was ready to start tuning the gun.”
Virgil continued: “You can change the powder charge slightly, and it won’t really make any difference, but if you change the bullet seating depth or the grip on the bullet, you’re going to see bad things happen fast.”
After a case has been fired a couple of times, another condition is created in the neck that requires sensitive feel. A tiny groove pressed into the neck by the pressure ring on a flat-base bullet causes the bullet to “snap” into place when it’s seated. Virgil emphasized that feeling the bullet slide down the neck and then snap into place told him everything he needed to know about whether that round was going to go into the group or not.
To sense these critical events, Virgil seated bullets in a Wilson straight-line tool BY HAND — not arbor press. He estimated that the seating pressure on his hand was moderate — perhaps 15 pounds. If seating requires significantly more pressure, the operation damages the bullet’s fragile pressure ring, bulging your groups. If the seating pressure is too light, he said you’re assured a mediocre .250" rifle.
[/ QUOTE ]
The Smokin Fur Rifle Club