Thread: What in the world?

Defo head seperation. And if new brass it is possible was run through FL die first. If the shoulders are bumped back beyond 0.010-0.020 then the brass can find it has too far to stretch when fired...leading to this problem. I'd check the amount of shoulder bump of a FL sized case.

Originally Posted by Tikka7mm08

Defo head seperation. And if new brass it is possible was run through FL die first. If the shoulders are bumped back beyond 0.010-0.020 then the brass can find it has too far to stretch when fired...leading to this problem. I'd check the amount of shoulder bump of a FL sized case.

That was my thoughts too and could be even be a many times fired case accidentally mixed up with the new cases.

Some more photos. I'm seeing a ring down on the web?

So that's a loaded one, here's another fired one that didn't separate

Get a bit of wire and have a feel around the inside where that ring is showing on that fired case just at the tip of your middle finger

If new hornady brass was used from the start of load work . New hornady brass headspace is 53.46mm i have seen once fired brass out to 53.93mm on tikka and sako rifles so it can only take 3 or 4 firings for separation to happen if brass has been full length size every time . Check headspacing in your rifle . hope this helps

Originally Posted by Rated M for Magnum

So that's a loaded one, here's another fired one that didn't separateAttachment 141255

Greetings Rated M for Magnum,
That case will separate next time so bin it. You can see a shiny bit of case just in front of the belt. This is the solid head of the case. The rest of the case looks slightly frosted where it has been pressed against the chamber by pressure. This is normal. About 2 to 3 mm into the frosted area you can see a brighter ring. This is a start of head separation caused by repeated firing with excess head space. Belted cases are supposed to head space on the belt but often do not. Also belted cases are often a little short to the shoulder so are always going to stretch a little on the first firing and more if the loader FL sizes the new brass before loading (this is a bad practice and should be avoided). True up the neck mouth with the expander button if needed but do not FL resize. Dies are often a little short to the shoulder especially for factory chambers. Only size enough to just allow the case to chamber and no more or head separations are bound to follow. Thanks for asking for help and advice, it is how we learn.
All the best Grandpamac.

That ring you can see will line up nicely with the seperate stub. Section a case end for end for a better view.

With a belted case like the 7mm RM it is often better to headspace off the shoulder rather than the belt. Different manufactures can end up with differing belt shoulder positions. If using the belt you can end up in no man's land with excessive case shoulder to chamber shoulder gap and unless you use something like the Stoney Point (now Hornady) headspace gauges you have no idea of the extent of that gap.

I had the same thing happen with Federal brass a couple of months ago. The same load I previously used Norma brass for several firings with out a problem.
Ended up pulling them apart and throwing out all the Federal cases.
Won't buy cheap brass again.!

If those dents in the separated case were caused by gas bypassing the case it would pay to check the chamber for gas cutting.
When a primer fails you get a nice little hole in your bolt face.

My guess with the dents is that upon firing when the head seperates the rest of case fires foward in the chamber rapidly witch compresses the case much like what happens when you bump the shoulder back to far when resizing.
Only a theory of course

Its a belted magnum which headspaces on the belt not the shoulder. This means any amount of over sizing the shoulders stretches the brass forward and thins the rear cup intersection where the brass is harder and more brittle.. resulting in that case head separation. Possible water or oil in the chamber could have also caused it as the brass didnt lock and seal to the chamber walls early in firing sequence the which those dents tend to point too..
If its new brass Id be checking it closely as it may be out of spec. If its reloaded brass then the resizing die needs backing out. If its old brass, check the rest of it for thinning lines or cracks above the cup.
Id also check the rifle out..check the head space is set up right and check for bolt lug wear and recession.

Thank you all for all your information and advice. I'm going to advise my brother to take his rifle, the empty cases, the sperated case and the remainder of the loaded rounds to the gunsmith he uses in CHCH.

The rounds were loaded/reloaded by a third party so hopefully they can figure out what to do moving forwards.

Thanks again everyone for your input, I really appreciate the sharing of experience and knowledge on this forum.

Originally Posted by Gkp

My guess with the dents is that upon firing when the head seperates the rest of case fires foward in the chamber rapidly witch compresses the case much like what happens when you bump the shoulder back to far when resizing.
Only a theory of course

Close Gyp,
What actually happens is that the force of the firing pin hitting the primer and the primer going of shunts the whole case to the front of the chamber. You can often see this with sub loads where the primer is protruding from the back of the case due to the low pressure. As pressure builds the front of the case grips the chamber walls and the case head is forced back over the primer to contact the bolt face. This is the point where the case may separate. If it does then the gas can flow forward until it gets to the shoulder that is still pressed tight into the chamber. The dents we see form at this point. Dents like that can also form with very low pressure loads. And it all happens in microseconds!
Regards Grandpamac.

So, grandpamac referring to your last post, is it correct that a slight leaky primer might actually be caused by a case sized down too much and not a hot load or loose primer pocket ?. I agree with your comments elsewhere that we should neck size only and not bump the shoulder back