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I'm forming 6.5 Remington Mag from 300 Winchester mag. Steps are: 1st step run into 350 Rem Mag trim die, 2nd step run into 6.5 Rem Mag trim die, 3rd step full length size with de-capping pin removed. No annealing required. Necks need turning/reaming. If I ream after 3rd step, neck tension is inadequate. I could outside turn after expanding neck, but to what size? Is this trial and error, or do you use the outside neck dimension as listed for the 6.5 Rem Mag after expanding neck?
Aim for 12 thou neck wall thickness.
I'm assuming that the brass is a lot thicker than that at the 2.1" mark of a 2.6" parent case.
12 thou should still have the neck touch sides in a full length sizing die.
You need a neck turning tool to get proper control over neck wall thickness, I don't think a reamer on it's own is the right tool for consistent results.
The loaded 6.5 rem mag should be .298. Load one of your newly formed brass and measure it. Subtract .298 from that and you know how much to reduce the neck.
What I would recommend is to make an accurate chamber cast of the rifle and turn to .001 loaded round dia under the chamber cast for a semi fitted neck. This will possibly 1) increase case life 2) lower case stretching and need for trimming 3)the tighter neck may increase accuracy.
It would be worth your time to load a dummy round without turning or reaming the neck, just to see if it chambers. I have a similar situation when converting 30-06 brass to 7.65 Argentine-- the neck for the Argentine brass sits where the shoulder is on the 30-06. Even though the converted brass has a thicker than normal neck, they still chamber and give excellent neck tension.
The internet has .298" as the maximum loaded rounds outside neck diameter. Outside neck turning is the best way to go.
Seat a bullet & measure OD.
Watch for donuts.
Important to have good concentricity after reducing the neck wall. OD turning tools do this better than reaming. I haven't needed to do it in a while, but I do it on my lathe. With only modest care, you can get better than .0005".
If you are using this ammo in just one gun then I would outside turn the necks to 2 to 3 thou less than the neck diameter of a fired factory round.
+1 - You would be amazed at the variance of factory new brass.Quote:
Originally Posted by dtknowles