RCBS dies, 175 grain Barnes X, 7mm Rem mag, brand spanking new Tikka T3. I got two complete head separations with accompanying flattened primers, and three others showing obvious signs of separation. I do not have the figures on hand right now, but worked up to a max load (every charge weighed) from the book (Barnes), initially with no visible signs of trouble. The brass is mixed, but has not been loaded more than 2 or 3 times in total. Even the fully separated brass was not "stuck" in the chamber...just fell out. I checked the resizing die, which had not been adjusted since the rounds were loaded. The press seemed to be "camming over" a bit more than it should have been. The Nosler book suggests that improper adjustment of the die can create such problems. Could I be setting the shoulder back a smidge too far and creating a headspace issue which in turn permits excess stretching of the brass, and subsequent flattening of the primers on the bolt face? I have reloaded lots of rounds for another 7mm using the same die, though with different loads altogether...a few different powders, no Barnes X bullets...no problems. My plan is to pull all the remaining bullets, and start with some lighter loads using new brass...might also run some factory rounds through to see what happens. Any other suggestions? FWIW, all the brass was polished, trimmed to length, chamfered in and out, flash holes deburred and primer pockets cleaned.
Case Separation diagnosis ?
- Thread starter icedog
- Start date
I do beleive Barnes had some issues with their Rem Mag data, compare it to other published sources.
Try doing partial full length sizing on your brass, you may be setting your brass into a loose head space situation.
Try using all the same headstamp of brass, do not mix and match.
Try the 160 Barnes the 175's are way too much for most anything you'll shoot.
Try doing partial full length sizing on your brass, you may be setting your brass into a loose head space situation.
Try using all the same headstamp of brass, do not mix and match.
Try the 160 Barnes the 175's are way too much for most anything you'll shoot.
Because headspace is controlled by the belt, it is not unusual for chamber dimensions in belted magnums to be on the generous side. There are also numerous reports that there can be a bit of variation in belt thickness. The separations that you are observing sound very much like an excess headspace situation. The flattened primers do not necessarily indicate an excess pressure situation. The headspace situation could be worsened by fl sizing, as you suspect. It is common practice to treat belted cases as if they were rimless for reloading purposes. After first firing, resize the case so that it will just chamber feely, but do not set the fireformed shoulder back any more than absolutely necessary, so that headspace is controlled by the shoulder, not the belt. Incidentally, I wonder if loading a maximum charge in mixed cases is a good idea? If case volume varies because of manufacturing differences, pressure and uniformity ae going to vary as well. If you have had two complete separations, plus a number of partials, I would suspect that you are going to see more in this particular batch of loads. Breaking the rest down for salvage of powder and bullets sounds like a good idea.
With belted & rimmed cartridges especially, I usually back the sizing die off of the 'cam-over' position by a good 1/4 to 1/2 turn, so as to only size the neck, and minimally size the body, without setting the shoulder back. This effectively headspaces the brass off the shoulder, which should greatly increase it's lifespan.
Eventaully after several loadings they won't chamber easily anymore. When this happens you start dialling your die in, 1/8th turn at a time until the cartridge just chambers smoothly. Then you've found your optimal size
Eventaully after several loadings they won't chamber easily anymore. When this happens you start dialling your die in, 1/8th turn at a time until the cartridge just chambers smoothly. Then you've found your optimal size
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