What would cause this?

[bersaguy]

Just loaded up some Gold Dots and Some Everglades JHP 115's over 6.5gn of Power Pistol to run thru the chronograph tomorrow. I ran across some strange brass among my mixed range pickup.


The last one there is the suspect brass next to a normal looking specimen. They're different headstamps, so I'm assuming the chamber did this upon firing. Has anyone else seen this happen? Would that be an oversize chamber or something else? Either way, there is a crease there after resizing, so I think these will have to go in the chuckit bucket

 

[243winxb]

Stepped chamber.

 

[JO JO]

as said above stepped chamber , my HK VP9 does that here is a generic picture of the chamber

 

[bersaguy]

That's a new one to me, what is the purpose of a stepped chamber?

 

[JO JO]

I think the idea is that it will have a better case seal and powder burn allowing better accuracy,

 

[Milt1]

Help me understand this! If the case is full length resized how does the case fit into the chamber with the chamber reducing as the case goes in. Seems like it would not fit all the way into the chamber; that it would go in fine until it hit the reduction in the chamber?

 

[bersaguy]

Help me understand this! If the case is full length resized how does the case fit into the chamber with the chamber reducing as the case goes in. Seems like it would not fit all the way into the chamber; that it would go in fine until it hit the reduction in the chamber?

It looks like the chamber is two diameters instead of being tapered to exactly fit the slight taper of the 9mm cartridge. So the stepped portion at the front of the chamber is the correct diameter for the mouth of the cartridge, and the rear of the chamber is the correct diameter for the head of the cartridge...and the middle is not so much. I guess that makes sense for early toggle locked guns like the Luger, extracting very fast and possibly at higher pressure. Could reduce the force required to extract the spent case. I suppose it makes machining easier, all straight tooling. Not sure why this would still be used on modern guns, other than to reduce cost of manufacturing. Seems like a "It's not a fault, it's a feature" type of situation to me.

 

[lordpaxman]

Just when you think you’ve seen it all! So what about the brass that’s been fired through it? It would seem to be dimensionally ok, assuming good neck tension, the next firing in a non stepped chamber would fire form it?

 

[bersaguy]

It's probably ok to reload, there's a definite crease I can feel with my fingernail where the step had been after resizing. Found a whole mess of them the other day. May load them up for use at ranges where I can't pick up my brass. I have to figure that step shortens the life of the casings. Definitely don't want the end of one of those to split and stick in my chamber

 

[mdi]

Hmmm. New to me too. Could you measure the OD of the "bad" cases before resizing? Interesting to see how much difference there is in the stepped chamber vs a standard chamber...

Googled "VP9 Stepped Chamber"; https://www.google.com/search?q=HK+...e..69i57j33.7283j0j7&sourceid=chrome&ie=UTF-8