Chronograph Test and Case Failure

[DenStinett]

Took my MG20 out to test-out the OC Custom Trigger and Ghost Ranger Connector
Very very nice
While we were out, we ran a few Chronograph Test out the Load I put together to run thru the CCU:
Xtreme 165gr RSFP, in front of 9.3gr AA#5, with Win LPPs, in Win Brass
Shot the MG20 and my Witness in its 3.5" Carry and it's 5.0" Longslide set-ups
3.5" avg = 1100 fps
5.0" avg = 1175 fps
MG20 avg = 1475 fps
Not bad for a fun / lite Target / Plinker Load

About 35 Rounds into the fun, we got a Hard Jam
Tried to chamber another Round and the same thing
Looked into my Case Catcher and found....The Web End of a Case
Took the CCU home and into the shop
With a bit of luvin', I was able to remove the Mouth End
Not sure of the Chamber went dry and I ripped the Case in two
Or the Case failed
I do know that the Chamber on this CCU is so tight, I really don't have to re-size the Brass to re-load it (but I do)
Here's the Case:

[The_Shadow]

How many times was it reloaded?
It could have gotten brittle, AA#5 is a faster power and being fast can snap the brass outward as the pressure spikes.  Starline does have a video about brass being damaged by faster burning powders.

[Pinsnscrews]

Work hardened was my thought too. I am wondering if the too tight chamber is not letting the brass flex enough also.

[The_Shadow]

If it is only this one casing it shouldn't be an issue, if it tends to do this again maybe something of concern.
Being a new chamber, it maybe a little rough and the brass imprinted into the machining marks and it got ripped in two during extraction.  Polishing or more use could help to smooth it out.

It is possible if this was a reloaded brass, that it had a small fracture and the second firing caused it to fracture the rest of the way.

What headstamp brand of brass was it?

Was this brass cleaned using liquid method?  Stainless Steel pins?  I am not a fan of the liquid methods especially when chemicals are used.  My reason would be that the chemicals can attack the brass on a molecular level.  One such chemical is ammonia.

Good luck, hopefully it will only be that one and others will be fine!

[DenStinett]

It's Winchester, brass not nickel
Twice fired, in the MechTech, resized after I clean and polish, using a two step process:
I first clean the Brass using Walnut and Rouge
Then polish it using Corncob treated with Midway Brass Case Polish, in my DYS Tumbler:

[RJPDVM]

You had a case failure. It looks from the photo that that area of the case is crystalized. The function of the 20 is recoil operated and doesn't have the horsepower to tear a case in half. A gas gun maybe. A recoil action has just the right balance to extract the case work the slide far enough to grab another cartridge and run back to battery. You can pretty much stop its function with heavy finger pressure on the back of the slide. So overall it seems to be a less than perfect case, which begs the question, was it only 1 and a fluke or is that lot subject to subsequent failures.

[DenStinett]

The one and only (so far)
This CCU has a VERY very tight Chamber, but I agree, the split does look a bit crystalized

[wadcutter]

 You got 1175 fps from a 5" witness and 1475 fps from a Glock 20 with the same ammo? Did I read that correctly? How long is the barrel on that G20?

[The_Shadow]

The MechTech MG20 CCU is not a Glock 20...Its a carbine upper that is used with the Glock lower and sports a 16" BBL

[gandog56]

I've blown 2 cases in my Mechtech. But I can't tell you how many times those cases have been reloaded. It has never blown a new commercial ammo case.

[DenStinett]

You got 1175 fps from a 5" witness and 1475 fps from a Glock 20 with the same ammo? Did I read that correctly? How long is the barrel on that G20?

The MechTech MG20 CCU is not a Glock 20...Its a carbine upper that is used with the Glock lower and sports a 16" BBL

As Shadow said:
Here are the three "Barrels" I used
The Witness Compact (Upper) and Longslide:


And my MG20-M4:

[wadcutter]

My bad 

[DenStinett]

My bad 

No probemo