I've had head case separation before but this is a different, I'm loading for a 257 Rob AI

The incipient separation showed up a little over 1/2 way up the case from the head

Arrows on photo show the bright rings, I cut one open to confirm, the neck on other is crushed to make sure I didn't reload it

Any ideas what caused this?

I'll make a guess at it....

1. You have way too much excess headspace.....the smith that chambered for the AI didn't set the barrel back a thread!

2. Only the rear half of the chamber received a fine polish after chambering and this allows the front half to firmly grip the chamber walls after the firing pin pushes the case forward and detonates the powder.....this forces the entire rear half of the case to pull away from the front half instead of at the web as is normal in excess headspace.....

Have a competent smith check your headspace.....this is a common error in chambering for the AI cartridges.

It does seem that Vapo nailed it(in the Head) on the First Shot.

I have had similar failures in my hornet (not my own original cases). My hornet chamber is rough and I have to lube my cases before firing or they just stretch. Some of those failed cases were already weakened and began to show the separation ring quite high up. I put it down to full length resizing by the previous reloader.

I would say this is in line with what vapodog has said.

Is this something that can develop over time? I've had the rifle since the 80’s; it is a Mod 70 XPR FW that I bought new in the box from a gun dealer, thought chambering was done at Winchester but I could be wrong?

Have had head space separation before but I attributed that to poor full length resizing, have not seen it since I started using Lee Collet dies

I was loading light w/ IMR 4350 & RL 15 (we haven’t had any Blue Dot or SR 4759 on the shelves since the election) to slow done velocity for predator hunting, could that cause this, know there is a danger with reduced loads but I did not go below minimums in my manuals

P.S. it is Remington brass

IMO this is a factor of two things

1. headspace and the amount of it and the increased headspace depending on your resizing practices.

2. The number of times a case has been resized and fired.

The last item may make the situation appear as though it was happening over time..

Correct the headspace and the problem will go away.

That narrows it down to one, this brass has been FF and then reloaded once, I threw all my old WW brass way after I had the FL resizing issue

Looks like I need to find me a gunsmith

If you get your chamber checked and get it fixed or find it IS the right length the next thing to do is make sure it is well polished. Then lightly oil your cases especially the front end. This will allow them to expand and slide without sticking to the chamber.

Abob.....it you chamber a factory round it should not chamber easily.....it should have to be forced a bit.....if it chambers easily the smith screwed up

Vapodog, I didn't notice it when I was FFing but I really wasn't paying that close attention -- would it be noticeable?

quote:

would it be noticeable?

yes.....very much so

Looks like I'm off to the gunsmith, assume they check with a type of gauge

take along a few factory loads with you and don't let them tell you the bolt isn't supposed to slightly crush the factory cartridges....most figure about .004 crush when closing the bolt on a factory round.