7x57 Mauser case length

[Battis]

I formed 7x57 Mauser cases from 30-06 cases (for a 1903 Remington Rolling Block). After firing, the overall length of the cases had shrunk. The distance from the head to the shoulder/neck is the same in each case, but the neck lengths vary. So, should I pick a length and trim the cases, or just neck size and move on.

[leadman]

The RB has a chamber that is not of the same SAAMI approved dimensions we are used to. Usually the headspace measurement is longer. The chamber may also be worn in the body so material has to take up that space when fired.
That said it is not uncommon for reformed cases to shorten when fired. My 7.65X53 Arg. reformed cases do this every time.
I fireform my cases with a fast powder in a small amount, fill the case to the top of the shoulder with Cream of Wheat cereal, put a wax plug in the mouth to keep everything in place and then fire them. An example of the charge I would use in the 7X57 would be 13grs of Unique. Load a couple and see if they fully form, if not increase the charge a little and try again.
I would neck size the cases you have already fired with a stout load to make sure they are fully formed then trim to length after firing.

[Battis]

I've seen that the case length should be from 2.235 (new brass) to 2.244 (older brass). The older brass that I fired, head stamped 7mm, remained at 2.244 but the 30-06 brass that I formed shrunk down to 2.222, 2.219, etc, all below the 2.235 listed for new brass. So, should I just neck size them and load them, or trim to a common length? Is there a point where they're too short?
Thanks.

[claude]

This will put your brass in a better light, Trim length 2.225, which leaves your "short" brass well within usable limits, trim to a common length and shoot away. Open the page and scroll and scroll.... all the way to the bottom and there are the spec.s I quoted.

Source: http://www.ballisticstudies.com/Knowledgebase/7x57.html

[Battis]

Great info. Thanks.

[EDG]

Use once fired .270 cases if you have some to make 7X57 brass. Expand the mouth a little so it drags when shoved into the chamber. Form a test case to the proper headspace length then trim the case mouth until you can get the over length case to chamber. Make several test cases until you know the shoulder is in the right position and the case mouth just clears the front edge of the chamber. These cases will be your pattern going forward.

When they are fired they will get a little shorter when they expand to fill the chamber. When resized they will get a little longer but probably not enough to touch the chamber front edge. Just keep shooting them until they are about .003 shorter than chamber when resized. When they get longer trim them back .002 or .003.

Tuning your brass like this gives you a good fit on the shoulder and a maximum safe case length based on that rifle. Do not use the cases in any other 7X57.
The manuals are fine for making ammo that fits everything. But you can fit your brass to one of these old antiques if you can measure.
Don't be surprised if your chamber has a longer shoulder and looks like an Ackley Improved chamber.

The Lee Collet neck die mentioned in the next post is an excellent idea for one of these rifles.

[opos]

I have always trimmed to 2.225 and then I use Lee Collet dies to neck size...I'm on my 4th batch of loads and the length is not growing requiring more trimming....I do "pre fit every case after neck sizing to make sure it fits the rifle The initial trim I did was after the first neck sizing

[Battis]

The 30-06 cases that I formed shrunk a lot. The fired (old) 7mm cases (FL sized before using) stayed the same length. I did a chamber cast but I think I'll do it again.

[blackthorn]

My book on cartridge conversions gives a trim-to length of 2.234 on cases formed from 30-06. The diagram in my copy of Nosler #6 manual shows a case length of 2.235. Good advice above on fitting the case to your chamber.

[leadman]

I form all the brass for my four 1891 Argentine Mausers and keep them in plastic ammo boxes with the label having the serial number of the gun they are made to fit. I am in the process of doing this for the six different 30-06 rifles I own.
I use one of my Lee Turret presses to load on most of the time so I may buy some more turrets and sizing dies and keep them loaded with the serial number of the gun on the turret. This will cost a bit but will cut down on having to readjust the dies.