What am I doing wrong with sizing brass?

[Bob Wright]

Compare your fired brass to those that have been FL sized and ready for loading. What are those numbers?
If you have any fired brass, does the bullet easily slide thru the neck?
As mentioned, neck clearance is probably at .004- .006 from chamber neck to loaded cartridge.
Do you neck turn/ream? (Possibility of a donut forming and distorting case during bullet seating as it did me....).

 

[JAYgs8163]

You seem to have a donut at the case neck/ shoulder junction. This is caused by the flowing of the 1st fired brass to fit the chamber (especially belted magnum). The MINIMUN clearance suggested between the case neck and the chamber neck is 0.003". That donut can grip the bullet tighter than you expected and cause dangerous pressures 'cause the bullet doesn't get released properly. The suggested remedy is to inside neck ream.
That's all I know about it as while I have checked the measurements of the neck as I asked you, and have reamers and such for the job, I have never had to neck ream.
Neck Reaming is only done on FIRED CASES BEFORE SIZING.
Sorry if this doesn't help.

I had thought of this but I don't see it and would a donut appear after only 1 firing of the brass?

 

[JAYgs8163]

Compare your fired brass to those that have been FL sized and ready for loading. What are those numbers?
If you have any fired brass, does the bullet easily slide thru the neck?
As mentioned, neck clearance is probably at .004- .006 from chamber neck to loaded cartridge.
Do you neck turn/ream? (Possibility of a donut forming and distorting case during bullet seating as it did me....).

I've never neck turned/reamed. I will check fired brass tomorrow and report back. Thanks

 

[Bob Wright]

I had thought of this but I don't see it and would a donut appear after only 1 firing of the brass?

Yes.
More with Ackley Improved or other wildcats but its worth checking for. You can usually feel the donut as the bullet seating force feels normal, then gets stiffer toward the bottom of the press stroke. I've not encountered it on my 7 mag yet.

 

[JAYgs8163]

Thanks everyone. I've got some good tips and some good reads to review. I appreciate the feedback.

 

[P7M13]

I'd bet a beer it isn't your neck diameter.
I only use a case gage for my semi-autos. Chamber test on my bolt guns.

I have experienced the same.
First instance was LC brass that was "softer". Dimensionally the same, seat a bullet and the body would expand a few thou at one of the shoulder junctions, or fatten at the case head.
Next was interference by the seater die. If my case was 1 thou too long, it would produce a shoulder bulge.
Only way to tell is to completely dimension a bunch of cases, after sizing and again after seating.

 

[DocDoc]

Use a felt tip marker on the case with a seated bullet. Put it in the gauge and you can see where it rubs. This is where seating a bullet is changing dimensions and keeping it from dropping into the gauge.

 

[Tree Farmer]

I had a donut form on once fired Lapua brass (.260 rem). Surprised me.

 

[misterc01]

When I have checked my resized round with a gauge and if it does what you are showing, I re-check my process to see why. Sometimes even checking the dimensions of that case against one that fit, I can't find a difference. If it is compressed, I remedy that, and sometimes just using a vibrating electric toothbrush ($3.00 at Wa-art!) settles the powder down enough to resolve that issue. If everything else checks out, then I go to my Lyman Ammo Checker. I found that if it fits, it shoots.

 

[bdyal1972]

Belted cases are known not to completely resize all the way down to the belt. Do a search on resizing belted magnum cases and read what Larry Willis has to say. What you are experiencing is not uncommon.

I CONCUR TWICE SIR!!!

 

[corsair4360]

Let me relate an experience of mine reloading a 7mm Magnum. The rifle shot really well (as I recall about 1"). After firing 3 or 4 times the cases swelled to the point that the brass when laid on a straight edge had swelled to the point the belt no longer touched the straightedge. This was over 40 years ago, I do not have the rifle or cases from it any longer.

Let the rifle tell you what it likes. Case lengths, diameter of the neck etc are all established by the chamber and action you are shooting. The rifle is the ultimate arbiter of loads for it.... specifications, etc are irrelevant for a specific rifle.

 

[jimbires]

I have another thought .

by chance your seating die body is adjusted down a little to far , and that's causing a crimp ? put a resized case in the press , raise it up the whole way . turn the seating die body down until it lightly touches the brass case , then raise the die up 1 full turn . lock it in position then adjust the seating plug to your desired seating depth .

 

[Dean2]

You have me curious now, let us know when you get it figured out. It is pretty clear that seating the bullet is what is causing the issue so it has to be either over expanded neck, crimp bulge or the pressure of seating is bulging the shoulder to body junction. Have you tried fitting a sized re-primed case and if it fits it is pretty limited as to what would cause this change from resized empty to loaded round.

 

[jshepherd61]

Picture of the round. View attachment 214784

Ok, so you said the brass will chamber prior to loading, is it fully chambered? Check the brass once you chamber and eject it! Is there any chamber marks on the brass? If not you have ruled out the brass! Now try loading a couple .10 shorter, will it chamber? If yes your throat may not be long enough for you current load or check the bullet it's self! May be the bullets a thou to big, wouldn't be the first time!