9mm stepped chambers

[ilikegunspdx]

Noticed that my stribog has a stepped chamber and started researching it. Looks like HK uses stepped chambers and some/all? newer model Walther 9mm pistols such as ppq.

Anyone know what other pistols have stepped chambers? Just curious.

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[tac]

Do you mean 'fluted'?

If not, please elucidate for us simple souls.

 

[ilikegunspdx]

I'm not sure if fluted is the same thing or not. The stepped ones leave a distinct bottleneck appearance to the spent brass and have a stepped portion of the chamber (front of chamber is smaller diameter than back). So far I've heard three different theories for it:

1. Easier to manufacture vs a tapered chamber.
2. Seals the tapered 9mm round better. Improved velocity and accuracy due to this.
3. Keeps original design of Luger round (and indeed the Luger p-08 pistol). Here is a copied portion of blog I found:

"apparently Georg Luger patented the offset obturation otherwise desribed as a 0.1mm chamber step in 1910, to ensure the chamber sealed gasses when firing a tapered case like the 9mm Luger in order for it to act as the bottle necked 7.65mm cartridge which accomplished this "See image attached"

Here is a spent case from the stribog as an example:

 

[tac]

Thank you. I had never heard of it before today.

 

[ilikegunspdx]

I didn't know about it either but couldn't figure out why stribog brass had that bottleneck shape and started heading down the rabbit hole ha ha.

 

[TTSX]

Makes me wonder about my HK p30. It's brass comes out with just a hint of a shoulder if you look for it. German just like the Walther, so wouldn't surprise me

 

[Certaindeaf]

Jeez, I wonder if the web on those is ruined. Have you reloaded some
of those?

 

[ilikegunspdx]

Jeez, I wonder if the web on those is ruined. Have you reloaded some
of those?

No I don't reload. There are some threads out there of hk shooters asking the same thing. I didn't read every single post but the jist I got from the threads I read: from experienced reloaders, they had no issues reloading the mildly bottlenecked hk cases. No experience myself. I can dig up the threads if ur interested. I think I bookmarked them all.

 

[Certaindeaf]

No I don't reload. There are some threads out there of hk shooters asking the same thing. I didn't read every single post but the jist I got from the threads I read: from experienced reloaders, they had no issues reloading the mildly bottlenecked hk cases. No experience myself. I can dig up the threads if ur interested. I think I bookmarked them all.

Cool. Not really interested but thanks.
I can load and shoot unsized .360 dia lead slugs in most of my 9mm guns.. was just wondering.

 

[DLS]

The step has no impact on reloading. Most of the time it will disappear after a trip through the sizing die. Even if a trace remains the bellling of the case mouth makes it irrelevant.

 

[Certaindeaf]

The step has no impact on reloading. Most of the time it will disappear after a trip through the sizing die. Even if a trace remains the bellling of the case mouth makes it irrelevant.

I use a lot of .357+ dia slugs.

 

[DLS]

You might have to bell the case mouth a tiny bit more than normal to eliminate shaving the heel of the slug, but that would be the only difference.

 

[Certaindeaf]

You might have to bell the case mouth a tiny bit more than normal to eliminate shaving the heel of the slug, but that would be the only difference.

Yea I do that. Wondering if it'd chamber a severely coke bottled round. See above.

 

[DLS]

A stepped chamber might cause difficulty chambering a load with an oversized cast bullet but the step in all reality is very tiny. I too load "oversized" cast bullets in 9mm (use a Lee 105 grain .38 mold without sizing the bullet) but find that the bullet gets swaged down smaller in the crimp station. Even if it didn't it would swage down in the bore upon shooting since we are talking only a few thousands over bore size and a lead projectile. Much like a powder coated bullet, where the powder coating adds a few thou to the final diameter.

This might be a problem accuracy wise, but these loads are used for close range drills from the holster and work fine in a Sig 365 and a G19. If I were doing bullseye type of shooting with these guns (and I wouldn't be) then the "oversized" bullet might be an issue.

 

[ilikegunspdx]

Very good info there dls and certaindeaf. Thx! One thing I was curious about is would the step cause some types of ammo (factory I mean) to hang up on the "step" as the round is loaded. But I guess the step is so small it would be a non factor like dls said.

So far I haven't had any malfunctions with anything I've shot but that's probably only about 5-6 different types or so and only one type of 147 grain. But have shot aluminum and nickel-plated brass cases fwiw (no steel). Lately I've been into the "recoil firing" thing and the stribog seems to really love going fast. Potential Ammo hangups should show up in that type of use eventually I would think.

 

[DLS]

Unless you are shooting wadcutter shaped bullets the nose of the bullet will have passed the step prior to any contact by the base of the bullet or the shell casing. So the nose would "funnel" in the bullet into the leade, so there should never be a hang-up because of this tiny step.