Bushing Size?

[bailey1474]

Ok, I've got all my brass for my 6-250 trimmed, neck turned and sorted. Now all I need to do is size and prime. I have .265", .266", .267" and .268" bushings for my Redding die.

I measured the neck diameter of a loaded round and it measures .268". Obviously this leaves out one of the bushings but which one of the others should I use? From your experiences does more or less neck tension make a cartridge more accurate.

Keep in mind that this gun is primaraly a bench gun and the magazine will never be used. I don't mind a very light neck tension as long as I don't have to worry about the bullets settling or runout increasing due to normal hauling around.

Thanks in advance,
B.J.

 

[Bart B]

Less neck tension reduces the variable in release resistance which means muzzle velocity spread will be lower. But one has to get a compromise between too loose a fit which may let the bullet fall out and what produces best accuracy. A good compromise may well be using a bushing about .002-inch smaller than loaded round neck diameter.

 

[Buffalobob]

THE SECRET

[ 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 ]

 

[Varmint Hunter]

Brass spring-back is normally about .001" after sizing. With that in mind the .266" bushing should give you the .001" of neck tension that seems to be about the norm for many bench shooters.

Personally, I am much happier with .002" of neck tension and would go with the .265" bushing if it were me. Sometimes a little more neck tension reduces SD. Either way, i'm willing to bet that you would not be able to detect a difference in group size, but it would be an interesting experiment.

 

[Centre Punch]

Bill,
Try the .267 bushing and if you can twist the bullet easily between thumb and forefinger move on to the .266 and so on untill you cannot twist the bullet easily, in my opinion thats all the neck tension you need.

Ian.