Should a 7mm Remington Magnum and a 280 Remington expander ball measure the same? The reason I am asking is my 280 Rem. expander ball is pretty scratched up and I was wondering if I could use a 7mm Rem. Magnum to replace it until I got another one.

If their out of the same brand they should be identical, other brands may not fit due to shaft size.

If it is out of an RCBS die they will fox them for free.

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If it's a Redding I highly recommend the carbide sizing button kit. I even managed to make the same kit work on a Lyman die as well.

RCBS will replace ANYTHING! No questions.

But my question is: How'd you scratch the sizing ball? This is a pretty critical aspect of the die. I clean my brass before it goes near a die. Scratches and dirt in a sizing die are death to the machine work.

The inside neck sizing button sizes on the out stroke. Ball fits into the neck, neck is sized and then the ball pulls the inside diameter to spec on the withdrawal.

Bullet diameter on both 7mm Rem. and 280 Rem. is identical. Sizing button should be the same for both. You could toss a micrometer on them.

Also, you may be able to polish out the scratches in your scratched button. 0000 steel wool and chuck the button in a drill. I polish mine with tripoli on a flannel cloth for a finish.

Slightly undersized button will result in more neck tension. This might improve accuracy. Burrs are a problem, but grooves in the button, should not be.

I won't say what kind of dies I have. I have a set of 260 Rem., 270 Win., 280 Rem., 7mm-08 and 7mm Rem. Mag. I took all of them apart and the 260 and 280 both had the ridges on them. The others were very slick. They were all the same brand of dies.