I recently had a problem that I don't know the cause of. I reloaded some federal brass for my 7mm rem mag. This brass was originally factory ammo fired in a friends gun, he doesn't reload and offered me the brass. I thought great, I love federal brass.

I have some rem. 150 gr pspcl bullets that I bought from midway. I have yet to get them to shoot well. I use Winchester large rifle magnum primers. For this particular load I was using imr7828 - 63 and 65 grains.

In a previous trip to the range, these two loads had produced the best groups, though nothing to write home about, with this bullet so I was trying to get a more accurate load. I checked the length of my chamber using a split neck case with a loosely seated bullet. I chambered the round to seat the bullet and extracted then measured. I did this several times and found an average length. I checked this length with the dowel in the barrel method. Same result. I seated the bullet so as to not touch the lands but not too deep as to have a light year leap.

The velocity of the rounds was not super fast at 2885 - 2894, an extreme spread of 9 and SD of 3.6.

The accuracy was just over an inch at 100 and right at 2 at 200. I was pleased with this since the best groups that I could get before were about 2.5" to 3". The cases extracted without undue effort, primers were not overly flattened. All seemed well. Then I looked at the cases a bit more closely.

Each one had the telltale bright ring indicating separation of the case head was right around the corner.

I didn't notice this until I had fired most of my rounds. Only 20 or so for this trip since it was getting hot. I quit at about noon with the temp at 85 or so humidity around 30. Slight breeze at my back.

I thought that maybe the brass was too long. I checked the max case length with a case that I had cut a piece of the neck off and seated a bullet then put the ring on the bullet, chambered the round, extracted, measured the length. I repeated this process to validate the measurement. The brass was 83.36 mm, chamber 84.2 mm.

I have had the bright ring before but only after having reloaded the brass for 5 or 6 times.

I have pulled the bullets and dumped the powder from this brass.

I just want to know what have I done wrong to get the brass stretched this far.

Any information would be greatly appreciated.

Thank you.

I suggest you try fireforming some in your chamber at lower pressures, then work the load up again. Sounds like something is setting up and artificial headspace condition. Same as if your dies were pushing the shoulder back too far. Double check, and see if they have been reloaded before.

I am unsure if my thoughts are correct, but someone here will straighten me out, I'm sure.
Case head separation is not caused by pressure, but by too large headspace. My guess is you may have oversized the brass, pushing the shoulder too far back on resizing. This wouls allow brass to flow forward upon firing.

jd- back off your sizer die a turn and try sized case in chamber.If bolt don't close do it again
with sizer down a 10 of turn and so on.leave caes unprimed and unloaded to do this.You may have gotten brass with short belt headspace and
you have to get brass out to chamber shoulder length-Ie headspace on shoulder.Some 7 mm cases have belt length .012 short of nominal size.
Thus if shoulder is back,case chambers a little ahead,When fired, case grips chamber, and base goes back against bolt as pressure spikes, thus stretching case ahead of belt.Ed.

Your friends rifle may have a max length chamber which combined with die on the small side and a biggish chamber in your rifle would start seperation going.

The condition you describe is due to excess headspace and not pressure.

The die (if correctly made) should not cause the condition no matter what you do. Assuming the die is correct, the problem is in your chamber.

Yes, backing off the die can correct the situation but you are then no longer full length resizing. BTW that's fully acceptable as long as the ammo fits your gun in the end.

It seems every time I run into this it's a flawed chamber.

While all of the above may be right, I have to ask. Did you check the unside of the cases with a stiff piece if wire witrh the end bent into an "L" shape? Sometimes, due to differences in chamber size, the die can produce a bright ring that does not necessarily mean a case head separation. If the base of your friends chamber was noticably larger than your rifle's, then a bright ring could appear when you resized.
I'm not saying the other answers are wrong, mind you, just bringing forth the options, and what I mentioned hadn't been said by anyone else.
The way I set my dies up for any bottleneck cartridges is to back the die off and slowly adjust down until the cases close with just a slight trace of snugness. Then, I turn it down only the very slightest amount further, maybe a 1/32 of a turn to allow smooth feeding. Any cartridge I shoot with a belt gets the same treatment so as to headspace on the sboulder rather than that idiotic belt. Brass lasts a hell of a lot longer than way.
Paul B.

If your friend's chamber had excessive headspace (SAAMI tolerences can be pretty "generous") there could have been too much brass already stretched from the case body before you reloaded it the first time. It only gets worse if the next firing isn't a crush fit in your chamber.

Thank you all for your replies and information. I did cut the brass apart to check the thickness of the case wall and found that on the ones I fired were very thin at the point of the ring. I then checked one that was fired in my friends rifle and it is also starting to get thin. I had the headspace checked in my rifle and the gunsmith told me it was fine. When I got the brass I tried to chamber it in my rifle knowing full well it probably wouldn't chamber. It didn't. Then instead of adjusting the die (Hornady) a little at a time, I assumed that I would need to full length size it. I think that is where I went wrong.

Again, thanks for all of the information.
Joel