Necking down RWS 7x57 to 6mm AI

[Elwood]

Could anyone give me the measurement of the neck thickness after they have necked it down? Before necking down the RWS neck wall is a very uniform 17.5 thou, after necking down with firstly a Redding 243 neck die without the expander and then finished in a Redding 6mm Rem FL die with expander removed my neck walls are measuring 22 thou! and the outside neck diameter is .262.

I then obviously have to expand the necks in order to turn them down and be able to seat a bullet. After they have been expanded the neck wall thickness is 19 to 19.5 thou and the outside neck diameter is .280.

Does all this sound right? I know I'm moving a lot of brass about but it looks like I have got to turn my necks down 5 thou (each side) to get to the desired .270 neck.

I have done a lot of searching on the net on how to go about this but no one has actually given measurements. I can't say I'm thrilled about taking such a long neck from 7mm to 6mm in one pass and have decided to use a 257 Roberts in order to help.


Ian

 

[Steve Blair]

It seems like a lot of work when Winchester makes 6mm brass. It does require some prep but I have been shooting it for thirty years with good results. I load to full pressure and get around 10-14 reloads.

 

[Elwood]

Steve, I have Win brass here as well, I just like the idea of being able to turn the necks to suit my chamber, basically the RWS brass turns a standard chamber into a tight neck and as this is a competition rifle I don't mind going the extra half yard.
It will also be nice to make a comparison of how the different makes of brass shoot, one thing for sure though is the RWS brass is as good as it gets, I have just ran 10 pieces over my concentricty gauge and the necks run out at 1.5 thou difference, the Winchester brass runs at a high of 9 thou.

 

[Steve Blair]

Neck runout prior to firing is a little misleading. After firing in a correctly reamed chamber most brass will show little runout. I am certainly not saying that Win brass is the best and it requires its share of prep, too. It is just that the procedure that you described sounded like the long way around.

Neck wall thickness could be an issue. As you are doubtless aware, the Win case is on the thin side. I had my 6mm chambers cut with a .271 neck for that reason. A light truing cut and it's good. If the RWS brass will get you to where you need to be, you might try the 5.6 X 57. That should be pretty straightforward.

 

[40X Guy]

I used Norma 7X57 brass and necked down in 2 stages for my 6AI, first in the .257 Roberts FL die with expander removed, then the 6MM FL die with expander removed.
After using a Sinclair 6 MM expander mandrel, the neck measured .274, I did not measure neck wall thickness, my chamber in my 6AI has a SAAMI .278 neck so seating a bullet got me at .275, perfect for my chamber with no neck turning and no signs of pressure. You are on the right track, turn the necks to fit your chamber. Remember to keep in mind seating the bullet will expand neck ~.001. You will have plenty of brass left after neckturning.

My newest 6AI has a .269 neck, and I am going back to the Win. brass on that rifle. They will need neck turned to fit this chamber. 6AI is a heck of a cartridge.


Frank

 

[Elwood]

Steve , I here what you are saying about the case necks being straightened out once they have been fired, but if the run out is minimal with virgin brass then it tells me that everything else is going to pretty uniform as well.

Frank, thanks for the information, I was just a little concerned that .280 after expanding was a touch on the high side. I guess RWS is thicker than Norma.

Is there any reason for using FL dies and not standard neck dies for the necking down process? I can only guess that the FL die holds the case tighter?

 

[40X Guy]

Yes, the FL die keeps entire case under control and sized so it will chamber like it should. And RWS brass is pretty beefy to start with. You will be able to reload several times over, and then some.

Frank

 

[Steve Blair]

Steve , I here what you are saying about the case necks being straightened out once they have been fired, but if the run out is minimal with virgin brass then it tells me that everything else is going to pretty uniform as well.

I use the NECO tool and have found no correlation between unfired neck runout and case wall thickness variance. There is a direct correlation between neck thickness variation and case wall variation. If the case walls and necks measure well and there is some neck runout, I ignore it.

If the thicknesses measure well, the case will be straight after firing. If there is significant case wall variation (more than .003"), relegate the case to secondary use. It will likely "banana" after firing due to the uneven walls.

 

[Elwood]

Steve, today is a good day, as I have just learnt something, thank you.