Removing the lip from the case mouth

26 August 2010, 19:28

dave-t

I have a .257R and after neck sizing the cases through a full length rezising die, there is a lip that forms right at the case mouth and I think it is giving me higher pressures than I should be having. The lip is tiny, and I can really only feel it when running a finger nail over the end of the case mouth, it is barely visible.

What is the easiest way to get rid of the lip?

Could it be that the ball expander is seated to deep and is them curling over the case mouth more than what would be typical?

I have not had any issues with this while reloading other cartridges, and am worried that the die may not be set up right.

26 August 2010, 19:37

Antelope Sniper

I would expect a simple campher and deburring tool to do the trick.
http://www.midwayusa.com/viewP...productNumber=789334

26 August 2010, 19:40

aliveincc

First, adjust the decapping stem to just pop the primer out. Then check the length of your cases. If this fails, try neck sizing only. The only real way for a lip to be forming is if the case is hitting/bumping something inside the body of the die.

26 August 2010, 19:42

plainsman456

Also be sure to check the length of the case to be sure it's not to long.
When de-burring wobble the tool side to side a little.it helps.

26 August 2010, 20:48

dave-t

Thanks fellas. I have been neck sizing only with a full length resizing die, but I'm faily certain that my decapping pin and expander ball are not tuned up to where they should be and it it rolling the case mouth out on the back stroke.

I'll check the case lengths again, and be sure to deburr.

28 August 2010, 20:29

Ol` Joe

quote:
Originally posted by dave-t:
Thanks fellas. I have been neck sizing only with a full length resizing die, but I'm faily certain that my decapping pin and expander ball are not tuned up to where they should be and it it rolling the case mouth out on the back stroke.

I'll check the case lengths again, and be sure to deburr.

IMO and opinion only without looking is the case is too long and is bumping the end of the die chamber and peening it over. The expander has no bearing on the outer lip of the brass and does not "roll" it under any circumstances I`ve seen in my 40+ yrs of screwing up ammo.
A good trimming and chamfer should cure the problem.

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29 August 2010, 00:26

SR4759

quote:
Originally posted by dave-t:
I have a .257R and after neck sizing the cases through a full length rezising die, there is a lip that forms right at the case mouth and I think it is giving me higher pressures than I should be having. The lip is tiny, and I can really only feel it when running a finger nail over the end of the case mouth, it is barely visible.

What is the easiest way to get rid of the lip?

Could it be that the ball expander is seated to deep and is them curling over the case mouth more than what would be typical?

I have not had any issues with this while reloading other cartridges, and am worried that the die may not be set up right.

New brass that has never been trimmed and brass that has been excessively tumbled in a rotary tumbler often has the case mouth dinged. It is best to deburr slightly. You can also remove it by use of a neck turner. I have never seen it bad enough to affect pressure but I really doubt that it does accuracy any good.

Don't worry if you don't get it all on the first deburring. A firing and resize cycle will iron some of it out to be removed by your case trimmer.