6mm remington from 7x57

[fg-machine]

it seems new 6mm brass has become impossible to find , excepting a few gougers on gunbroker .

with spring nearly here and summer around the corner i need some new cases or else my trusty 788 is going to miss yet another summers groundhog hunting .
so it looks like forming cases from 7x57 is on my plate , so a nice simple question from those in the know .

what worked out best for you ... inside reaming or turning the outside of the neck ?

[EDG]

Measure your chamber neck to find out how large it is.

Try forming a few pieces in one pass.

If that does not work form the neck of a few cases with a 6.5X55. Set the 6.5X55 die with a 6mm case and back up the die about .010 to stay off of the shoulder. Then try a 6mm die.

If that does not work you can try a 257 Roberts after the 6.5X55.

It is an easy process but you will have to learn what works with your brass.

I recently tested this with a new die just for the learning process. I have a good die selection so I made a pass with a number of dies just to measure the head to datum length.
My process started with .270 brass that was originally intended to be formed to 7x57. The fired .270 neck is almost exactly the same size as a loaded 7X57 neck.
I have the neck diameters of the FL , form and trim dies that I used. You can pick the various sizes if you have other dies to make the steps from one step to the next.
You may be able to do your forming in one pass. About 1972 I formed 100 30-06 Match cases to 25-06. I had no intermediate dies so I just formed the necks about .100 per pass.

To test this on a 7X57 case I dug out a 40 year old WW 7X57 case that I refused to reload because it had a very bad bulge from being fired in an old Spanish Mauser with an oversize chamber. I used a little bit of Imperial lube on the case. I did not have enough leverage to size the neck without tipping my work table so I backed the die up and formed the neck about .100 per pass. The case took 4 passes to form in my RCBS 6mm trim die. It looked ok. If you chose this method it may vary some depending on the temper of the brass. After forming be sure to anneal the case neck and verify that the brass will safely fit your chamber.
I do not ream any cases without a reamer die. Since my case form is a not for profit activity I avoid investing in reamers and reamer dies at the current retail prices when I have beau coup neck turning tools. I do not have a reaming set up for the 6mm Rem so I would turn the brass if it is too thick. Then I would anneal. Hard brass is much easier to machine with a nice finish so anneal after the neck machining. Then make sure your cases will fit your chamber necks.

Here are some 7X57, .257 and 6mm Rem die neck diameters. Note the trim dies are about .010 larger than FL dies and because of this if you have both die types, you will see some duplicate or overlapping diameters from one caliber to the next.







7x57-.257- 6mm die family neck diameters




























necks
Deltas 1 step
Deltas 2 Step





7X57
CH Form
.323









7X57
RCBS Trim
.315
.008


End of 7x57 forming



7X57
RCBS FL
.306
.009
.0170





.2570
Pacific Trim
.291
.015
.0240





.2570
RCBS Trim
.287
.004
.0188
End of forming for .257



.2570
RCBS FL
.278
.009
.0130





6mm
RCBSTrim
.277
.001
.0102





6mm
RCBS FL
.266
.011
.0120
























A RCBS 6.5X55 FL die is about .284 to .286.














A RCBS 6.5X55 trim die is about .010 larger.

[Mauser48]

If you have a 257 roberts die run the 7x57 through that then into your 6mm and trim. If you do not have a 257 die run it straight through your 6mm die then trim. Use a good case lube like imperial sizing wax. After its trimmed put it in your gun to see if it fits nice. If its too tight you will need to neck ream or turn. Im not sure if you would need to aneal after. It couldnt hurt though. Good luck, im in the process using 7x57 to make 257 roberts. I found that i dont need to neck ream. You could make the 6mm out of 257 a little easier but 257 is pretty hard to find too and its exoensive.

[C. Latch]

Based on my very little experience with case forming, you might not need to ream or turn. Especially if you are using Winchester or Remington brass.

YMMV.