G20 KB! - Ideas on what happened?

[wifecallsmegrumpy]

Thinking outside the curve, any possibility the bullet was slightly oversize ? I found a cast bullet the otherday from a commercial caster that was out of spec.

[sqlbullet]

Pinching the case mouth is what would be needed in an out of spec bullet I would think.  If they can move outta the case they will swage right down.  Small pressure spike, but I wouldn't expect to see this.

Now, if it were large enough that it was pinched in the case by the front of the chamber that would give you the spike and explain the horizontal split.

[Yondering]

Didn't somebody on the GT 10mm reloading forum post about some soft brass from Starline a while back? This sure seems like a very similar scenario.

That load is not hot enough to cause the case blowout you experienced, unless there was bullet setback, or you used the wrong powder (AA5 instead of AA7?).

This does illustrate why you should test new hot loads with the magazine removed.

[pasky2112]

It wouldn't surprise me if it were the case.  I took every precaution I know of and have always been using.  There's no way I had a powder mix up.  Not only do I use only a single container of 1 powder in it's original container at my bench at one time, all others are locked up in another room.  I take the time to clean my hopper, bar, etc when changing powder so as not to have even 1 kernel of another powder mix with the next.  I'm borderline neurotically paranoid about that stuff b/c I know how easy mistakes can happen when I am not that careful.  And even then, a flawed human makes a flawed product.

I checked the remaining rnds from the blown mag and their OAL is unchanged... 1.255"-1.257".  I attached a pic of the blown case plus 2 of the same batch and 1 factory after the KB.  Would you have stopped after seeing these cases?

Thanks for responding,

- Dave

[attachment deleted by admin]

[Yondering]

Assuming your pic is showing the feedramp area, I sure wouldn't have felt any concern about those other cases. Seems like whatever the issue was, it might have been specific to that one round, and not the load in general.

[Taterhead]

Maybe your crimp wasn't tight enough.If a bullet sets back upon chambering it will cause pressure to go way to high.If you want a hot load maybe using AA 9 is a better way to go in a glock.It fills the case and is a slow powder.Always good to make sure your crimp is good.Sometimes a die can back out a little.10mm's have strong recoil springs and I put a pretty good crimp on my handloads.I push my bullets into the side of my bench after setting the crimp and make sure they hold then measure to check for setback.Glad you didn't get hurt.

I totally agree about Accurate no. 9. It is my go-to high performance 10mm powder. Good advice there. I also check often for neck tension in the matter that you describe.

Neck tension is critical for preventing setback. Crimping a straight wall case has little effect on setback. A heavy crimp merely shrinks the diameter of the bullet and can be counterproductive. Crimping to the point of engraving the bullet is too much. Also, crimping will not overcome improper neck tension. Crimping heavily will squeeze down the bullet diameter at the case mouth. The brass springs back slightly and tension is lost.

[Vice]

Maybe your crimp wasn't tight enough.If a bullet sets back upon chambering it will cause pressure to go way to high.If you want a hot load maybe using AA 9 is a better way to go in a glock.It fills the case and is a slow powder.Always good to make sure your crimp is good.Sometimes a die can back out a little.10mm's have strong recoil springs and I put a pretty good crimp on my handloads.I push my bullets into the side of my bench after setting the crimp and make sure they hold then measure to check for setback.Glad you didn't get hurt.

My first thoughts as well.  As this was the cause a few KB's when I shot IPSC in another life.

I test my crimps the same way.

[REDLINE]

It really sucks when stuff like this happens with no definitive answer as to why.

[Vice]

Thinking outside the curve, any possibility the bullet was slightly oversize ? I found a cast bullet the otherday from a commercial caster that was out of spec.

That should be expected!

Commercial casters use machinery that are spitting bullets out.  They can't eyeball EVERY single bullet that goes out the door like a hand caster.  There are just too many variables with heat vs cooling vs barometric pressure vs temp, vs machinery issues that come into play.

With cast bullets, expect SOme defects, it's going to happen.

However, if you start to get more that a few per hundred, look for another caster.

[sqlbullet]

And, as a recent article in handloader points out, lab pressure testing by CCI, aka Speer, in 1959 shows that increases of even .010" will only cause a 2000-3000 spike in pressure.  They tested bullets sized .352" to .362" in a 38 Special Pressure barrel.  The .352" loads averaged 12,000 PSI.  The .362" loads averaged 13,000 PSI.  In between they say values as high as 14,000 PSI and as low as 11,000 PSI.  (Handloader #280 pg

This level of change alone should not account for a blown case head.  Maybe in concert with a bunch of other factors, but by itself it won't.

[pasky2112]

It really sucks when stuff like this happens with no definitive answer as to why.

It does.  It's like a random crime.  it doesn't matter what you have/haven't done... it just happens.  But I still learned a few new tips and am blessed to not have been maimed. 

Thanks to you all for sharing.  I hope this thread helps others that come along, as well.

[REDLINE]

After rereading this thread I will say this (as others have commented on as well);

Use a beam scale for greatest accuracy.  With my Redding #2 beam scale I can easily discern charge weight differences of under .05 grains.  On my relatively brand new Hornady Bench Digital Scale, forget it.  I'm not saying the digital is not generally accurate, as it is.  But every once in a while it's at least .1 grain off.  With digital scales this happens easily just by temperature changes!  Which is the reason the owners manual for my digital scale says to not use it till it's been turned on for at least 15 minutes just for the circuitry to warm up to a stabilized temperature.  Plus since I don't work in a climate controled area, the overall temperature in the room changes throughout the day. 

Also with digital scales, especially when weighing to the nearest tenth of a grain, you want the scale to be as level as possible for most accurate and repeatable readings.  When it comes to deadnuts accuracy and repeatabilitly, a beam scale is the only way to go.  At the very least a good beam scales gives more peace of mind when working up new components and recipes of them.

Heck, the way I've been doing things so far, I first weigh up a charge on the beam scale and then still double check it on the digital scale.  And that's partly just to get me to see if I've screwed up by not setting the beam scale to an intended charge weight that I meant to have it set to.  I know, anal.  But it's because I don't even trust myself.  We're ONLY human, right?

[Bret]

I really appreciate this thread as I'm getting ready to start loading 10mm for the first time.  I'll definitely be extra careful.

Neck tension is critical for preventing setback. Crimping a straight wall case has little effect on setback. A heavy crimp merely shrinks the diameter of the bullet and can be counterproductive. Crimping to the point of engraving the bullet is too much. Also, crimping will not overcome improper neck tension. Crimping heavily will squeeze down the bullet diameter at the case mouth. The brass springs back slightly and tension is lost.

+1, well said.  The purpose of a taper crimp is to remove the flare from the belling step, not to help hold the bullet.

[Intercooler]

Doesn't anyone make a scale you can set to +/- say 2gr's that will give an alarm or something? I don't reload but would for sure search something like that out. If that doesn't exist I think I would just weigh them when finished before putting in the box.

[DM1906]

Doesn't anyone make a scale you can set to +/- say 2gr's that will give an alarm or something? I don't reload but would for sure search something like that out. If that doesn't exist I think I would just weigh them when finished before putting in the box.

It isn't the scale.  A scale is used for checking charges, not creating them.  Some dispensers have a scale, that checks the powder weight as it's being dispensed.  Most aren't accurate at a speed for anything other than (slow) single stage handloading.

Powder charge volume checkers are available for progressive and turret type presses.  In almost all cases, they will detect double charges and very light charges.  If set up correctly, they'll always detect a double charge or a light enough charge to cause a squib.

Weighing complete cartridges is rarely helpful for detecting over/under charges as little as 2 grains.  Unless all of the components are weighed before loading, it's essentially useless.  If using recycled brass and bulk target bullets, they can vary more than 2 grains, even with a correct powder charge.  Other factors of the handloading process can be equally as dangerous.  Handloading is a package deal.  We have to get it all right, every time, or bad things can happen.  There's a very fine line between an "unpleasant experience" and a full house KB!  Most "Kaboom!s" you hear/read about are in the realm of an "unpleasant experience".  I've seen the real thing more than once, and have yet to read of one here, or the other forums.  Bruised hands and scattered pistols don't count.

The most dangerous risk with handloading, no matter how you do it or what equipment you have, is distraction, and it can happen at any stage of the process.  Grab the wrong powder, fail to verify the load recipe and dimensional data, check the bullet weight, use incorrect primers (small pistol, small pistol magnum, small rifle and small rifle magnum are all exactly the same size), for example, and bad things can happen.  I handload a couple dozen caliber/cartridges regularly, so I'm at a higher risk compared to someone who loads only one with the same components.  Even when you do everything right, unexpected things can happen.  Usually it's minor and uneventful, and serves to give yourself a swift kick in the seat.  Other times, it can be a component failure, and the KB! still happens.  Hopefully, it won't be catastrophic.  Secondly, bad advice will get you into trouble.  Just because something works for one person doesn't mean it work for everyone, and every firearm has unique characteristics.  If it can't be verified by published data or extensive personal experience, it can be a recipe for disaster.