Forming 6mmAI cases from 7x57 Mauser

The Norma 7x57 brass is far better than the 500 Remington cases I ordered when starting my 6mm Ackley project.   Neck thickness was very inconsistent on the R-P cases.   If you decide to put up with the extra work of necking the Norma cases down, you won't be disappointed.  Here is my procedure for making 6mmAI brass from 7x57.

1.  Lube the case necks, then run the case into a standard .243 Winchester die with the expander removed.  This will only neck down about 80% of the length of the neck, then the die shoulder hits the case shoulder.  The sloping 20deg shoulder of the .243 die acts like a funnel, starting the reduction easily.

2.  Switch to a 6mm Remington FL die, no expander.  Re-lube the case.  Run the case fully into the die.  This will get that last 20% or so of the neck length reduced, and shape the shoulder. Note: You can start the whole process with the 6mm die and skip the .243, but it sure makes it easier for me.

3.  Try to close the case in your rifle action.  If it will not close, screw the die down a little more and try again.  You may need to repeat this step several times.  The action must close tightly, in order to insure proper headspace.  Make sure your lugs are lubed good.  I have also used a Redding 6mm Ackley shoulder bump die to get the shoulder back.  The case will look a bit odd - having a bit of rounding in the shoulder.  This will easily assume the proper shape upon firing.

4.  You will almost certainly have to neck turn the cases.  There is a definate thickening of the brass in the neck when reducing from 7 to 6mm.  Use an expander to neck the cases up if they won't fit the mandrel on your neck turner.  My rifle has a standard 6mm neck, .276", and I have to turn.  You could end up with very dangerous pressures if you don't turn them.  You should have .003" of total clearance with a bullet loaded, for release & safety.  When you measure the total with a bullet seated, be sure to try all the bullet brands you intend to shoot.  The boxes may be all marked .243, but you will notice that some of the custom bullets will be 1/2 of a thousandth (.0005) larger at the base.  The BR guys may use less clearance, but two smiths and several shooters recommended three thousandths to me.  If you have the standard neck size, you can almost equate the effect of having a "tight neck" gun.  I now have three in the clear.  When using the Remington brass, I was getting anywhere from 6 to 10 thousandths in the clear.  Not good for accuracy.

5.  The last step is to fire form. If your gun has a custom barrel, you should probably just load up and go hunting. Mine has not shown much accuracy fire forming with bullets.   Having too many rounds through the barrel as it is, I now fire form using Cream of Wheat. Click here if you want to read about that.

This rifle has proved to be a learning experience.  I may have expected too much from a factory barrel.  It will now consistently shoot in the .low to mid .4's, with the occasional two and three's thrown in to keep my hopes up.  It sure did not start out that good. The two things that helped my accuracy the most was switching to Redding Competition dies and Norma brass.  Get a set of the bushing dies, even if you don't want to fool with the Norma brass.  Those dies cut down on my run-out considerably, but don't plan on using them until after fireforming.

Read the Loads from Henry Bruns page for his case forming info.

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