Making 257 wby brass from 7mm wby brass

Put a very heavy chamfer on the outside of the case mouth as an aid for the neck entering the smaller dimension.

I used Lee Sizing wax in the tooth paste container, which worked much better than the Imperial sizing wax. Cases should be formed perfectly, necks slightly longer, do not use expander mandrel in the process.

As someone else mentioned, check neck thickness.

I had a reamer ground by PTG so I could neck down Winchester 264 Win mag brass and have the correct neck length in the formed cases. The reamer was also ground with only .030 freebore. I shot 100's at 3850 on 10T, 26" barrels producing 3/8" groups with 6x24 scope.
 
Can you just size the 7mm brass with the techniques stated above, and load them with a healthy powder charge? Or do they have to be fire formed first? Sorry for the ignorance, I am new to fire forming.
I am not sure if you mean 7mm rem mag or 7mm weatherby.

When I was making cases from 7mm rem mag brass, I would just size the brass in the 257 weatherby die, and then load a light load to fire form it. The shoulder needs to be fire formed.

When I did 270 weatherby brass to 257 weatherby, I just sized and loaded as normal because it was already a weatherby shoulder.
 
I am going to use 7mm rem brass, sorry being unclear.
How light of a load? 4-5 grains or so under max?
I have formed 7 Rem Mag brass, you should have the Weatherby Radius shoulder after sizing. It doesn't need to be fire formed. Look at the picture of the 460 Bee brass I necked down to 338-378 that I posted earlier. Both the first stage at 378 and the final stage at 338-378 have the radius shoulder. That wasn't on the 460 brass I started with. On top of that belted cartridges head space on the Belt. Yes the shoulder will form a bit on firing but it is not critical nor will the re-sized 7 Rem Mag brass change much anywhere else.

Use your newly formed brass with a mid point load and test different COAL for best groups. This will give you fire formed brass. Once you find the best COAL, work up in powder charge till you find the highest velocity node, that produces good groups. This way you aren't wasting powder and barrel life.

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Ok, I would like to clear up some confusion on the forming 257 Weatherby brass from 7 mag brass, and I would only use NEW Winchester, PMC, or AGD....NO federal or Remington as they are softer in the case head.

Use Lee Sizing wax in the tooth paste type of container, and let it sit on the cases for a few minutes before running the brass through the die. For this application, Lee was far superior to the Imperial.

If you will put a heavy chamfer, not a deburr on the outside of the case mouth, then gently run the brass into the 257 Weatherby full-length sizer(I used Forster), you will have a 100% perfectly formed case with ZERO bulges, etc. you want the chamfer to just about go through the entire thickness of the brass neck wall, and I consider this critical.

My method is to size the brass down in small increments. Size a little, back off, size a little back off, perhaps 4 small steps instead of just one large step putting a lot of stress on the tensile strength of the brass.

If you have dents in the case, the die ring is covering up the vent hole, move that die ring location.

I never lost a case with the above method, never. I credit this to the heavy chamfer and the use of Lee Sizing lube in the toothpaste container.

The neck will be shorter on the formed brass, with the result of carbon in front of the case mouth in the neck of the rifle chamber. The carbon in front of the case mouth is an important issue if you are mixing factory and formed 7 Mag or 264 Win brass. The carbon ring in the chamber will act as a Crimp at some point on the case neck as that dimension will be smaller. I use a Bronze bristle brush/good bore solvent to get the carbon out of the neck and inspect with a Teslong bore scope. If you do not use regular maintenance on the carbon, you may have to use a brush on a rod, spun by a slow speed 1/2" drill.

I found 250 once-fired 264 win cases from a guy over on 24hr campfire. The web dia was larger in the test rifle those cases were fired in, compared to my reamer. So, I ran the 264 cases through a 7 Mag small base sizer without the expander ball where the neck was not touched.

Then I formed those 250 cases with the 257 Weatherby Forster full-length sizer, with the lee sizing wax on the outside and wax applied to the inside of the neck to ease the trip for the expander ball. Brother and nephew are killing deer and hogs with that brass now.

Their rifles are nothing real fancy, just hunting rifles on non-trued 700's, Boyd's laminate stock, #5 taper, X caliber 9 Twist barrel, a chamber with .030 freebore. They shoot 110g Accubonds and 115g Berger vld hunting at 3600 on 25.5" barrels with a Gentry muzzle break. Recoil is so little, they see the bullet impact on the animal with water flying off the hide, and the bullet impact after it exits. They are ready to get rid of a bunch of their heavier kicking rifles.

Note: the formed brass as it comes out of the Forster Full Lenth sizer with the Lee Sizing wax being used looks like brand new factory-formed brass. They worked up a load with the brass as it came out of the die with groups 3/8" and smaller, then hunted.

None in the family has had a deer do anything but fold up on the spot with the 257 Weatherby, and all of our rifles have either zero to .030 freebore, using R#22 with fed 215's in all guns. I shoot 100g Hornady and 100g Partitions and have killed quite a few with the newer 100g Nosler ballistic tips(3850 fps on a 26" bbl).

I hope to try the Speer 100g Hot Cores next...hogs.
 
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So I just did my first batch of ADG 7mm mag today. Some very interesting results to say the least. I shot 2 groups, one with turned necks and one without. Both groups were single digit SD, unturned was 7.6, turned was 3.6. Used 62 grains of H4831 with a 110 eldx to fire form just to see where I am at, Hornady book says 65.2 is max charge at 3300ish. My average on the unturned neck group was 3280, my average on the turned necks were 3300. Which is where the book says I should be at 65.2 grains, ADG is great brass and is going to save me some powder.
 
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I tried some virgin 7mm brass through my die, and this is how it turned out compared to the factory Weatherby case on the left. Pretty normal? Or not so good?
 
Mine were fully formed. The case on the right looks like it has longer headspace than the case on the left, ?

Also, what brand of brass are you forming? I used Winchester.

My die was set to full length size the 257 Weatherby brass for my chamber, I lubed the winchester brass, neck and shoulder with Lee Sizing wax that comes in the tooth paste tube.

Love to hear your comments.
 
It was virgin Norma. I used a Redding .257 Bee full length die. I just tried to run it through the die with one shot lube. They went through the die smoothly. I also tried to rotate them and do a little press at a time, and got the same result
 
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