Case head separation.

[greenejc]

I just had the same thing happen 2 days ago with 1x fired factory loaded Hornady 7mag cases. I thought it was my load as well. I then went and bought a box of their factory ammo with 162 EldX. If I looked close I could see the beginning of it on the brass. After I resized the brass I loaded and had complete case separation. Looked identical to yours. I have not had a chance to dig further into yet but I had planned on calling hornady in the near future.

That's an incipient problem with 7mm Rem Mag brass because it headspaces on the belt. A lot of manufacturers make the chamber a little too long, and you get case stretching on the first firing. Why they do this is a mystery to me, though. I think they use the belt and then just get sloppy with the rest of the chamber.

 

[Skidly_50]

Unfortunately it is. I threw all of it away that wasn't loaded already. I saved one to try and measure but after getting a comparator kit. I can see it's aways off. I hope that solves my problem. Now just need to see if the FL die will work or if I have to buy just a neck.

i use neck bushing die, then run them thru my rifle, any that are tight i then resize with a body die using competition shellholders.

 

[dennisinaz]

No need for neck sizing dies. Your dies are more than likely fine just set wrong.
Use { TDOT's post #27 suggestion}. Let us know what you find.
Good Luck

It is not a good idea to use the full-length die any way other than screwed down tight against the shell holder. IF you let it float, it can cause huge fluctuations in the amount of sizing you get due to differences in brass. Mic McPherson explains it real good in his reloading book. Recommend you get a set of Redding competition shell holders that are each successively taller. This way you can set the die up properly and still maintain the correct headspace.

As a quick check, you can take a piece of masking tape and tape it to the base of the shell. Use an exacto knife or equivalent to trim it. Then try and chamber the case. Add tape until it is tight. You can measure the tape to get your headspace. Tape varies so measure the tape first. You can use a caliper but a micrometer is better. I use shim stock that has been laser cut into discs to check. Most accurate results are with the ejector removed.

 

[Priley]

Sounds like your sizing die might be set to deep and you are bumping the shoulder back far enough to change your head space. Have seen this in a friends 6.5 CM

 

[chickm1]

This was every other shot. That one being the worst of it. Most of the rest you could just see the crack starting. I only shot 5 or 6. The worst of it was I had loaded 20 to go test the ES and SD. So I had to pull them all and throw the brass away.

Wow! Is it a bolt gun?

 

[tdot]

It is not a good idea to use the full-length die any way other than screwed down tight against the shell holder. IF you let it float, it can cause huge fluctuations in the amount of sizing you get due to differences in brass. Mic McPherson explains it real good in his reloading book. Recommend you get a set of Redding competition shell holders that are each successively taller. This way you can set the die up properly and still maintain the correct headspace.]

I've never read or seen this being a problem before. Do you by any chance have an excerpt from the book? I'm curious to know more.

How much variation are we talking? Is it only a problem between different mfg of brass? Or is the case to case variation enough to cause problems?


I only use one type of brass and lot per cartridge. When my brass changes, all my settings change. Maybe I've just been getting lucky?

 

[25WSM]

Denissinaz your joking right? Dies should only be used locked down touching the shell holder. Please tell us that was a joke. Because a die needs locked down in the place where it just sets the shoulder back. Running the die down to the shell holder and locking it is just the thing that causes problems like this. In a perfect world where every gun chamber is dead nuts on and every die is dead nuts on it could work. But tolerance stacking can make a die not able to bring the shoulder enough or way to far. I have to take .010 off the bottom of a lot of dies just to get them to size any setback. 95% of dies will not touch the shell holder when setting back .001 to .003
Shep

 

[antelopedundee]

That's an incipient problem with 7mm Rem Mag brass because it headspaces on the belt. A lot of manufacturers make the chamber a little too long, and you get case stretching on the first firing. Why they do this is a mystery to me, though. I think they use the belt and then just get sloppy with the rest of the chamber.

I expect that they cater to the factory ammo purchaser rather than the reloader. By making the chamber a scosch longer they ensure that most or all factory ammo will chamber.

 

[Mram10us]

It is not a good idea to use the full-length die any way other than screwed down tight against the shell holder. IF you let it float, it can cause huge fluctuations in the amount of sizing you get due to differences in brass. Mic McPherson explains it real good in his reloading book. Recommend you get a set of Redding competition shell holders that are each successively taller. This way you can set the die up properly and still maintain the correct headspace.

As a quick check, you can take a piece of masking tape and tape it to the base of the shell. Use an exacto knife or equivalent to trim it. Then try and chamber the case. Add tape until it is tight. You can measure the tape to get your headspace. Tape varies so measure the tape first. You can use a caliper but a micrometer is better. I use shim stock that has been laser cut into discs to check. Most accurate results are with the ejector removed.

I don't agree. If my die is .004" from bottomed out, what am I missing out on? .004" at the base not being resized means nothing compared to the shoulder of the round being .004" short

 

[Swiftkill]

Its gotta be from too much head space. Has to be. I would use a full length sizer and just turn it down into the press just enough to chamber and then another 1/16 or 1/8 turn. Partial size with a full length sizer , or , if you are neck sizing, it should match your chamber even better. If you truly have excessive head space and the first firing stretches enough, it could weaken the case enough. I would compare shoulder datum lines between a fired case and a factory unfired case or a full length resized case. That is the simplest way to know.

 

[Mram10us]

Its gotta be from too much head space. Has to be. I would use a full length sizer and just turn it down into the press just enough to chamber and then another 1/16 or 1/8 turn. Partial size with a full length sizer , or , if you are neck sizing, it should match your chamber even better. If you truly have excessive head space and the first firing stretches enough, it could weaken the case enough. I would compare shoulder datum lines between a fired case and a factory unfired case or a full length resized case. That is the simplest way to know.

If it just chambers and you turn it down 1/16, you are back with too much headspace. That is why you use something to measure the snug round to compare.

 

[sturner]

Sinclair bump gage will tell you the shoulder bump measurement
I still think it's a brass problem not a shoulder problem

 

[Bob Wright]

That's an incipient problem with 7mm Rem Mag brass because it headspaces on the belt. A lot of manufacturers make the chamber a little too long, and you get case stretching on the first firing. Why they do this is a mystery to me, though. I think they use the belt and then just get sloppy with the rest of the chamber.

The parent case was the 375 H&H cartridge. It was designed to chamber 100% by head spacing off the belt because it was for dangerous game. On my 7mm RM, the shoulder would move as much as .016 if I remember my measurements correctly. It's just designed into it.
Old technology.
Never separated one though.

 

[25WSM]

To the op, do you have a way to measure your shoulder bump? Until you can measure the fired case to a sized case you won't know why you have this problem. Any kind of metal sleeve that is able to fit over the neck, preferably close to the middle of the shoulder but not necessary. Stick it over the neck and measure with your dial calipers trying to square everything up as you do. The sized case should really be no more than .003 shorter.
The world record holder at Williamsport PA 1000 yard range has told me he sets back his wsm .007. I run my wsm at .003. I know that when you start bumping .010 you will start wrecking brass.
The whole deal with belted mags is to set headspace the same way you do any other cartridge. Off the shoulder not the belt. Belted mags get a bad wrap because people set the die to the shell holder and just let them rip without checking how far they bump. I wish reloading manuals would put more time and effort to show people how to use bump gauges and how important it is to not guess what you have. Almost every customer I build a rifle for or teach them more advanced reloading techniques don't know about measuring bump.
To the op again, please find a way to measure that bump and let us know and it will help us get you right.
Shep