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This is the .309 diameter steel neck sizing bushing from L.E. Wilson, part number B-309. It's the interchangeable insert that drops into a Wilson bushing neck sizing die body and sizes the outside of your case neck down to a precise diameter. That precision is the whole point here. Instead of over-squeezing the neck and then dragging an expander ball back through it, a bushing sizes only what you want to a set dimension, which keeps the brass concentric and extends its usable life.
Neck tension is the interference fit between your sized neck and the bullet, and it's one of the biggest levers you have for consistency. The way most reloaders land on a bushing is to measure the outside neck diameter of a loaded round with a good micrometer, then subtract the tension they want, usually around .002 to .003 inch, to account for brass spring-back. The bushing that gets you to that final number is the one you grab. A .309 fits a specific window of loaded-neck measurements and desired grip, so make sure your math points you here before ordering.
These bushings interchange freely across Wilson bushing-type neck dies, so you can keep a small set on the bench and switch between cartridges or brass lots in seconds. Different brass brands and even different production runs vary in neck wall thickness, which shifts the bushing you need, so a lot of handloaders keep one size above and one below their target on hand. That makes chasing the perfect tension a quick swap rather than a guessing game.
Machined and ground from polished steel, the B-309 is built to hold its dimension through plenty of sizing cycles. It's a small part that punches well above its size when it comes to repeatable chambering and tighter groups at distance. If you're already running a Wilson neck die, this is the kind of tuning piece that earns its spot in the kit.
Measure the outside neck diameter of a loaded round with a micrometer, then subtract the neck tension you want, usually about .002 to .003 inch. The number you land on is your bushing size. If that math points you to .309, this is your bushing. Keep in mind that brass brand and lot can shift the result, since neck wall thickness varies.
It's designed to drop into L.E. Wilson bushing-type neck sizing die bodies and interchanges freely among them. It is not intended for other brands of bushing dies, which often use different bushing dimensions. If you already run a Wilson neck die, the B-309 seats right in.
A bushing sizes only the outside of the neck to a set diameter, so you don't over-work the brass or drag an expander ball back through it. That means better concentricity, more consistent bullet grip, and longer brass life. For precision rifle shooters, that consistency often translates into tighter groups.
A lot of handloaders keep one size above and one below their target on the bench. Because different brass can call for a slightly different bushing, having a couple of neighboring sizes lets you fine-tune neck tension without waiting on another order. It's a cheap way to stay flexible across brass lots and cartridges.
| UPC | 815145024992 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | B-309 |
| Shipping Weight | 0.02 |
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