7x57 Mauser brass

[Battis]

I'm forming 7x57 Mauser brass from .30-06 brass for my Remington Rolling Block. From what I've read, for proper headspacing, after cutting to length and sizing the case, you should expand the case neck with a .30 caliber expander button, then size the case down until it chambers (to move the shoulder forward.
So, is the expander button a specific die or can I use (for example) a 30-40 die that doesn't touch the case but does expand the case neck?

[Ben]

Why do all that.
When you're forming the case, that is your opportunity to set the shoulder to the correct position for ideal head space.

I form and shape the case to 7X57 dimensions, but I do it gradually ( .002 at a time ) until the case is a " snug " fit in my chamber. Once you've established the correct die setting for your particular rifle, you can lock the die down and make many of them. If I need to thin the neck a bit, I do it by outside neck turning. Works for me.

Ben

[Battis]

I think the problem I'm having in my brain is the length of the case. If I cut it to length before sizing, it will lengthen as I gradually size it (30-06) down to 7X57...right?

[EDG]

Try this in 5 parts.

1. Sacrifice 2 to 5 cases by trimming them shorter than necessary.
2. Push the shoulder back on your process development brass until you get your FL die set exactly right. Lock your die.
3. Push the shoulder back on your production brass with a trim die if you have one.
If you don't have a trim die rough trim all of the cases leaving them about .030 too long. Push the shoulder back with your FL die.
4. Trim to length.
5. The first time you FL size after firing in your rifle check the length and trim again if necessary. When the cases are blown out to fit the chamber they often get shorter.
Don't be surprised if your RRB chamber is not the same shape that comes out of your loading die. If your chamber is different just neck size your brass with a 7mm 08 or .284 Win die.

Don't focus on getting the length perfect before forming the brass because it will change some and it is not predictable for every case.
Once you have them formed plan on trimming to final length. Make sure the long necks are removed on the cases you use for setting up your die.
You do not want the neck of the set up cases hitting the end of the chamber.

If you don't have a .270 once fired .270 brass is excellent for the 7X57. The fired necks are already the right size. The shoulder just has to be pushed back.

I think the problem I'm having in my brain is the length of the case. If I cut it to length before sizing, it will lengthen as I gradually size it (30-06) down to 7X57...right?

[NoAngel]

Creating a false shoulder works, but you can just as easily use a good cast bullet and have it engage the rifling firmly to hold the case back when fireforming.

[leadman]

Size the case a little at a time, try it in the chamber, close the front breech block and then see if the hammer block will go under the front breech block and contact the firing pin. There should be no resistance to closing the front breech block as this may prevent the gun from firing. The RB has no camming effect like a bolt action so the case has to fit. Trim your cases to max length as they will probably shorten when fired. Also when you seat the bullets/boolits make sure the overall cartridge length is not too long and they are hitting the rifling as this will cause misfires also.

[ScotMc]

I make 7X 57 from 06 for a 7X57 Ackley Improved. I use a trim /form die- RCBS:
http://www.midwayusa.com/s?targetLoc...rsApplied=True
I lube the case body with Imperial sizing die wax below the shoulder using a 7x57 case as a guide as to where the reformed shoulder will be on the case to avoid dents/creases. I use graphite on the case neck inside and out with the Imperial cases lubing kit- small ceramic balls with graphite on them. I start with the trim die just touching the shell holder. When the cartridge is all the way into the die, I remove the excess neck with a fine tooth hack saw 32 TPI, then use a file to trim it flush with the top of the die. I check the case with a headspace gauge for a 7X57 and make the necessary changes by moving the trim form die up or down as needed. Once you get the form die correct, the process goes fairly fast. This is a quicker way to form up your brass and I have had little wasted 06 cases in the process. The cost of the trim form die is around $36.00 from Midway.
You can always use the 7x57 sizing die to bump your shoulders back a little bit after forming and trimming to achieve the proper head space for your rifle. Hope this is something you can use.