Cases with inexplicably short headspace after sizing

[Jumbopanda]

I was resizing a batch of twice-fired 300 Blackout brass that I had formed from 223 cases, and came across a very strange issue. Out of about 320 pieces, 4 had their shoulders bumped a LOT farther back than any of the others (0.010"-0.020" shorter). At first I thought that I might have over-annealed some of the cases, so I took a test case, purposely over-annealed it by heating it until it glowed orange, then sized it. Surprisingly, the headspace on that case did not change. So I'm really puzzled right now as to how a few cases could have had their shoulders pushed that far back. This stinks because now I have to go back and check headspace on all of the brass to make sure there are no more like that.

[Tatume]

There might be a buildup of lube in the sizing die.

[Jumbopanda]

There might be a buildup of lube in the sizing die.

The cases in question did not show up at the end of the sizing session, but rather randomly in the middle. I'm using a mix of lanolin and 99% isopropyl alcohol sprayed in a fine mist, which results in a thin, even coat of lube, and doesn't cause any buildup. I did inspect and clean the die and couldn't find any signs of excess lube.

[oneokie]

Check the case heads for burs/deformities that could cause the case to sit higher in the shellholder. Also check the shellholder for debris in the recess that holds the case.

[williamwaco]

Did they stick in the die?

Sounds like they were setting on top of the shell holder instead of IN the shell holder.

I have done that a time or two.


.

[s mac]

How would you extract the case from the die if it was not in the shell holder?

[Jumbopanda]

I'm pretty sure I just figured out what happened. During the last range trip I had a few issues with my Micro 7's extractor not wanting to slip over the cartridge rim, which resulted in the bolt not being able to close. Not knowing what was wrong at the time, I slammed the bolt forward trying to close it, and that's most likely what caused those 4 rounds to have their shoulders set back.

Mystery solved.

[popper]

One okie nailed it. Annealing won't cause that. Slamming the bolt won't either. If it would, you have a major gun problem.

[243winxb]

I slammed the bolt forward trying to close it, and that's most likely what caused those 4 rounds to have their shoulders set back.
This does happen. In fact, the firing pin strike can set a 223 rem shoulder back .006" in a Savage Axis. Some of the old bolt actions, would do it also, by just closing the bolt to hard. Bolts had over travel.

[detox]

Mixed brass will cause inconsistant head spacing. Different thickness and hardnesses will size differently. Try using brass from the same lot. I like the softer Remington brass (from the same lot;))

[Echo]

What was the overall length of the subject cases? Could it be that the necks are .010-.020 too long?

[popper]

243winxb Can't happen - unless the chamber is loose and then when you fire it goes to full HS. Yes, you can bump the shoulder a couple thou, but they would all be close to the same, not 0.01-0.02" diff. OP made 300 from 223, could have made 4 short, with a lite load the shoulder didn't get blown out. I still maintain it is a sizing/die problem. Wish my AR 308 would set HS when chambered.

[williamwaco]

How would you extract the case from the die if it was not in the shell holder?


Takes a little dexterity and a little fiddling.

You remove the shell holder from the ram.
You then raise the ram to just below the head of the case.
You then align the shell holder carefully so you can slip the top of it over the cartridge case rim and the bottom of it into the ram - at the same time.
Then: Extract normally.

Yes, I have made that mistake several times.

[Baryngyl]

Takes a little dexterity and a little fiddling.

You remove the shell holder from the ram.
You then raise the ram to just below the head of the case.
You then align the shell holder carefully so you can slip the top of it over the cartridge case rim and the bottom of it into the ram - at the same time.
Then: Extract normally.

Yes, I have made that mistake several times.

Yes, but then he would have definitely noticed that.

I took it he was asking how he could have sized it normally (press it in, withdraw it) and not known if it was on top of the shell holder.


Michael Grace

[s mac]

That was my point also.

[Jailer]

How are you measuring your headspace?