Don’t know how it happened…

I was shooting a few leftover loads yesterday from a match on Saturday when,  Boomoo!! I somehow managed to cram enough powder in a 6GT to push my 109 to 3350FPS.  I typically run 2825.  Bolt was really hard to open, but I managed. Primer was obviously blown out and the case wasn’t going anywhere without a rod.

I can’t double fill that case, but I somehow managed to fill it to what had to have been the brim. I don’t remember anything being tough to seat and I glance down every case before it goes in the press… all my charges looked normal coming off the RCBS Chargemaster Supreme.

Bolt looks good, extractor and ejectors seam fine… anything I should worry about or double check?  Falkor 7even action.

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Damn glad you are ok. Not sure what else could take a hit from that except maybe your firing pin and extractor. Next time you fire a round check that first piece of brass for any strange dimensions.

Good luck.

Good call… I went out and grouped the last 18 rounds. Shot just the same and rifle functioned just fine. Just put the calipers on everything. Case dimensions are consistent with the others before the bang. Offending case expanded 5-6 thousandths at just about every measurement.

Going to tape this case to my press to remind me to pay attention.

That’s quite a bit of expansion. Good idea for the reminder!

How are you measuring your powder charges?

Did you load a caliber, using a different powder, prior to starting this reloading session? Any remnants of a pistol powder left over in the bottom of your powder measure will blow shit up.

Double check your scales? Misreading scales can have consequences. I use RCBS check weights to ensure I'm not off. My eyesight is horrible at close range, I need all the help I can get.

Post your load data, with overall length. Jamming the bullet in the rifling will spike pressure.

Did you have a barrel obstruction? A "dud" on the previous shot and not inspect the bore to make sure it cleared the barrel? A cleaning patch in the bore?

I never run hot loads. IMO, there isn't any reason to do so. If you want to go faster, get a bigger gun.

As I climb the ladder, I knock out primers and inspect the top edge to make sure they aren't forming a lip. A fired primer will start to form a lip as the very first sign of high pressure. By the time you get to firing pin extrusions and flat primers, you are way past "hot".

I'm glad you didn't lose and digits or put an eye out.

No to everything. I had a chrono capturing every shot, nothing strange until this cartridge. I measure B2O every third bullet I seat. I’m about 40K off the lands. I run these well below max charge, like I said 2825, some people run these north of 3K. I’ve never come close to seeing any sign of over pressure until this one as I don’t think I’ve ever gone above 2,900.

I let my RCBS Chargemaster Supreme warm up for a half hour before I calibrate it every single time. I’ve never had anything but Varget in this dispenser.

All I can figure is I somehow filled that case. I’ve definitely accidentally double charged a couple times, but there is still 20ish grains of powder sitting in the funnel after it fills… I don’t pull that funnel off… I just dump it back in the hopper with funnel still on there then remove the funnel and tap the case a bunch with the funnel emptying the case, then take a look inside.  If I just pulled the funnel off it would make a mess I’d immediately notice.

A few weeks ago I had a case overflow. At first I thought my measure broke.

Turned out there were a few pine needles and spider webs in the brass.

I was wondering the same thing... I've found dry media caked in rifle brass before. Figured it was because some water was still in the case after wet tumbling. I make sure cases are dried in the oven or hot sun before going into a dry media tumble now....

Pull random samples and weigh the charge.

That is scary, glad OP is OK.

I was going to laugh and call BS on this.................  until last night.

I was loading some primed brass, that were the remains of some pull down ammunition.
Put the powder in a tray of the brass and was looking at the depths before I moved on and seated bullets.  
One case was full to brim.
After playing with it to figure the issue out........... ended up sectioning the case to get the piece of brass schmuck/debris out of it.
It was pretty big, especially for a 223.    

Luckily the powder showed high, otherwise I would've loaded it.  
That brass schmuck piece would've pushed pressure up....................  who the #### knows.

I’ve had that thought about spiders in my cleaned brass that I have sitting in opened Greek spam cans.  It certainly could steal case volume.

Hard to believe some inert junk in the case would cause that kind of spike.

Any chance you got one wrong/heavy bullet mixed in?
Even factories aren't perfect.

Edit... I don't wet tumble.  Once my dry media is used up, the first real symptom is clumping up in the bottom of bottleneck rifle brass.
I don't try to push it too far now; life is too short to worry about that. Once it's getting significantly dark, I replace it.

I’m pretty certain by now that it was tumbling media in there. I wasn’t as diligent checking before… I’m pretty sure some slipped by me.

The best way to do that is to empty the media out of the tumbler and tumble everything for a few minutes.