Primary cause of a neck separation?

[Ignition Override]

This happened yesterday, and the .308 case has been reloaded twice before the incident. The bolt matches the rifle, and the field gauge has excellent results. Yes, I read four hours' worth of info about five issues regarding the Spanish FR8, and am very familiar. 'Roger that', it is an actual FR8, and the powder loads have been at the minimum (41 gr.) . Now using powder which is very similar to H380.

The brass had no external signs of any stress (beforehand).
Each time after I trim the cases down to the 2.015 max. length, I then smooth out internal and external burrs with the hand tool, using a few turns.

Having already reloaded over 1,000 .303 and now about 600 .308, this first separation is interesting.

 

[MtnCreek]

Have you measured the case neck after firing? It is possible the chamber is oversized at the neck and this would not show up with a chamber gauge. If it was just once, I would suspect a bad case.

 

[243winxb]

Brittle brass? How many times was brass trimmed?

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[Dthunter]

Bizzare indeed!

 

[popper]

Don't know what an FR8 is, but you really trim 308 brass? Size 1 with the expander removed and mic the neck, check the expander size. Maybe overworking the neck.

 

[Varmiter]

243winxb, I think has hit the nail on the head. How many time has the brass been trimmed?

If brass is ‘growing’ the excess metal you trim off is coming from somewhere.

Chris

 

[Edarnold]

You say you are using a minimum load? Are there any signs of the primers backing out in the fired rounds? At very low pressures, it's possible for the striker+primer to drive the case forward enough to push the shoulder back, then either the pressure builds enough to stretch the case back out to fill the chamber, or the case stays short (base to shoulder length) and the next loading is with a round that has excess headspace.

Or the original loads were with mercuric primers. (Really WAG!)

 

[arizona98tj]

The OP stated.....

This happened yesterday, and the .308 case has been reloaded twice before the incident.

I'd assume he started with new brass. Not likely it was trimmed more than two times.

 

[243winxb]

Each time after I trim the cases down to the 2.015 max. length,

2 loadings, 2 trimmings with brass over max. both times?? Thats a problem. This is why i ask how many times trimmed.

 

[Waywatcher]

So the rifle has acceptable headspace, that is good.

What is the headspace of your resized cartridges? In other words, how far back are you pushing the shoulder?

 

[Ignition Override]

Thanks very much for the responses.

Having used new brass, I have no system to determine how many times brass was trimmed.
The first reloading seems to always require hand trimming back to 2.015 or less.

Doing it by hand, the trimmed brass is sometimes 2.00-2.10 or so, after rotating the trimmer a few times as I hold the brass or nickel-plated cases.

When the event happened, we were puzzled that the next round refused to chamber. There had been no other indications of anything odd when using the problem round.
My inspections are mostly rotating the brass, looking for any neck cracks, unless markings show multiple reloads (internal paper clip check done).

Waywatcher: To clarify, the field gauge does not allow the bolt to turn one bit, in either FR8. I do what the RCBS instructions recommend, by rotating the die until it touches the ram, then rotating the die another 1/4 turn (max.). Will need to look up how to measure the headspace after resizing.

 

[popper]

Expander plug in the die pulls brass from exactly were post #3 has the break. If the neck gets sized too small the plug will pull lots of brass. Mike the OD of a fired case and a sized one(without plug), expand it and mike again. You need a case gauge to properly check the HS and set your die.

 

[Welding Rod]

Are you lubing the inside of your case necks before sizing?