Im curious what everyone is seeing for shoulders. New Hornady vs once fired
300 Win Mag shoulder growth
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I think it really depends on how your chamber what built. Some people are headspacing off of the shoulder on the customs others off of belt. Peterson developed the 300 win long to try and minimize case growth on the first firing.
Be super careful when resizing to not oversize, .0015 .002 max or you will have a case head separation.
Be super careful when resizing to not oversize, .0015 .002 max or you will have a case head separation.
FireFlyFishing
Well-Known Member
That really depends on your chamber.
From what I'm reading it seems fine. Bought some factory ammo to get an idea. I will get some Peterson long and go from there. Not seeing any pressure signs on this one !
I used norma. In mine I was never concerned about first firing shoulder growth. Shouldn't use virgin brass for belted magnums for load development anyway. So I just fire formed 100 cases and started development after that.
MagnumManiac
Well-Known Member
This is the truth without all the BS associated with gun rags and other MYTHS.
Shoulder growth on belted cases DOES NOT matter how much it is one little bit. It DOES NOT cause case head separations, it does NOT stretch the case at all. What you need to know is that SIZING belted magnums requires precision measuring and KNOWING how to adjust dies for CORRECT shoulder bumping.
I have seen between .016" growth to .026" growth in some action types/brands.
I build my own custom chambers using and basing my reamers on the military A191 chamber, which reduces shoulder growth to a maximum of .010", does it change the possibility of case head separations, no, but it definitely produces tighter tolerances upon firing. I have used the same dimensions now on 264WM & 338WM, it works very well. These 2 generally grow between .016"-.018", not a huge difference, yet it makes sizing a breeze.
Cheers.
Shoulder growth on belted cases DOES NOT matter how much it is one little bit. It DOES NOT cause case head separations, it does NOT stretch the case at all. What you need to know is that SIZING belted magnums requires precision measuring and KNOWING how to adjust dies for CORRECT shoulder bumping.
I have seen between .016" growth to .026" growth in some action types/brands.
I build my own custom chambers using and basing my reamers on the military A191 chamber, which reduces shoulder growth to a maximum of .010", does it change the possibility of case head separations, no, but it definitely produces tighter tolerances upon firing. I have used the same dimensions now on 264WM & 338WM, it works very well. These 2 generally grow between .016"-.018", not a huge difference, yet it makes sizing a breeze.
Cheers.
RD57
Well-Known Member
My 338 Win Mag has .005" headspace using the belt and Winchester brass. With virgin W-W Super (1992) brass there was .028" headspace based off the shoulder. I fire formed my brass by jamming the bullets in the lands on the first & second firing. Being a new rifle & cases and jamming the bullets I started with the minimum recommended charge and after the first firing the shoulder did expand out, but it was about .006" from being fully fire formed to the chamber. Based on the brass and the chronograph data I upped the charge for the second fire forming load and got some great looking brass and excellent groups on the target!
Anyway, I didn't have an issue with case head separation. I do like picking up range brass for comparing and adding to my collection at home. I do have some 300 WM and 7MM STW brass that is showing incipient case head separation. It would be interesting to learn what their rifle and brass headspace dimensions were to figure out what the issue(s) were.
Anyway, I didn't have an issue with case head separation. I do like picking up range brass for comparing and adding to my collection at home. I do have some 300 WM and 7MM STW brass that is showing incipient case head separation. It would be interesting to learn what their rifle and brass headspace dimensions were to figure out what the issue(s) were.
MagnumManiac
Well-Known Member
There is no such thing on a belted magnum…
Headspace is in the belt datum, not the shoulder…
Another believing falsehoods, there is absolutely no reason to jam bullets on a belted magnum…ever!
I form 375H&H brass into several Weatherby cases, the easiest being the 375 Weatherby, just chamber the H&H and out comes a Weatherby, because the headspace is controlled by the belt.
Cheers.
VarmintBob
Well-Known Member
The only mythology I see in here is that noise about "shoulder growth" does not matter. There is no reason to not treat a belted magnum the same as any other bottle neck cartridge. A belted magnum can headspace on the belt if you want it too. But it can just as easily headspace on the shoulder if you size cases to make that happen. As many have said, just push the shoulder back a couple thousandths. Brass with a taper always stretches when you fire it. The stretching eventually leads to head separation. I have never seen any brass that could be re-used forever. Eventually the case head separates. When a sparrow lands on the golden gate bridge, the cables stretch. Otherwise, every so often I resize belted cases using a Larry Willis collet die just to size down all the way to the belt.
Curious what does cause case head separation?
308plinkerVT
Well-Known Member
Repeated "excessive" resizing, as others have alluded to in minimal resizing tactics needed for belted cases.
If this is true what causes case head separation?
If the brass doesn't flow forward from the belt area why does the brass get thin and separate just forward of the belt?
I love MagnumManiac's knowledge and experience, he is a wonderful help here on the forum but this is the one thing I think he has wrong.
On his 375 example there isn't much shoulder for pressure to act on to stretch the brass but in the 90's on a 264 win mag I have had case head separation and the brass was thinner just forward of the belt. I maybe ignorant to what caused it but I'm pretty sure it was the brass flowing forward from the belt area.
