Click adjustment for Forster Benchrest seating dies.

[Heath Robinson]

I have Forster Benchrest seating dies in two different calibers.

For those that don't know them, these are similar to their competition dies in that they have a floating "chamber" that align the case with the bullet before the seating process starts, but they do not have the micrometer adjustment feature.

I have found that they give me reasonably good concentricity (although I suspect that has more to do with case quality and condition than die design) and excellent seating depth consistency, but they are rather difficult to set to the desired depth.

One can buy the micrometer heads but they are (by my standards) relatively expensive. And my experience is that once I have a load I tend not to fiddle with seating depth that much.

I did some measuring and found that the OD of the die body and the thread of the adjusting spindle of the two dies is the same. So I made a setup that bolts/clamps onto the existing die and gives me adjustment inciments of very nearly 0.0005" per click.

Once the die is set I can lock the spindle using the original lock nut and remove the adjuster mechanism.

Attachment 35489

Attachment 35490

[Skaaphaas]

0.0005”? Geez louise. With what do you measure that?

I have the same dies. Chose it over the micrometer specifically because, as you point out, they’re expensive and I don’t fiddle with seating depth once it’s set. But going through a seating depth exercise with these have proved hard.

[Heath Robinson]

0.0005”? Geez louise. With what do you measure that?.

That's a calculated value based on the measured thread pitch and the number of clicks per revolution. It's not exact because the thread pitch doesn't divide into a whole number.
The thread on the stem is 0.25" - 28TPI
I settled for 72 increments on the adjusting ring, which should in theory give me increments of 0.012599mm (assuming the thread pitch is perfect which is unlikely). So it's not perfect, but it's close enough that I can measure a cartridge and calculate an adjustment and be reasonably sure of ending up within a thou of where I wanted to be, which is more than good enough for me.

[Heath Robinson]

0.0005”? Geez louise. With what do you measure that?

I don't. And as I said, it's not exact anyway. It's not possible to get it "perfect" because the thread pitch (28TPI) does not divide into a whole number once converted to a linear increment. All I am after is to be able to measure a loaded round and calculate an adjustment that will get me to within 1 thou, and it does that well enough.

I have the same dies. Chose it over the micrometer specifically because, as you point out, they’re expensive and I don’t fiddle with seating depth once it’s set. But going through a seating depth exercise with these have proved hard.

If you have somebody who could machine one up for you, I would be happy to give you the drawings.

[Skaaphaas]

I don't. And as I said, it's not exact anyway. It's not possible to get it "perfect" because the thread pitch (28TPI) does not divide into a whole number once converted to a linear increment. All I am after is to be able to measure a loaded round and calculate an adjustment that will get me to within 1 thou, and it does that well enough.


If you have somebody who could machine one up for you, I would be happy to give you the drawings.

Ah I see. Makes sense.

Thanks for the offer, I’m likely not going to go through this exercise again but will keep the possibility in mind!