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Jim Watson
08-23-2018, 03:08 PM
I found in my mixed fired brass a 9mm with an obvious bottleneck.
I recall reading here that H&K and maybe Walther cut their chambers with a stepdown in the neck.

Is the neck tight to resist bullet start, increase pressure, and increase velocity? (As Sig did with a tight bore in the P6.)
Or is the rear chamber large for dirt tolerance?

farscott
08-23-2018, 03:27 PM
Looks like it dates all the way back to Georg Luger. https://www.waltherforums.com/forum/pps/16573-pps-chamber-tapered-stepped.html


he 9mm Parabellum cartridge case and its chamber ordinarily have a slight continuous straight taper. However, some chambers have been machined to have a straight, parallel-walled section, as visible in the photo. Its purpose is to extend the time during which the chamber is obturated as the cartridge case is extracted. (The seal formed by a taper breaks almost instantly.) Georg Luger patented the idea in 1911, and it was used on practically all Luger pistols made by DWM and Mauser through WWII, as well as on some German submachine guns


An email to Smith and Wesson, including an attached photographs of the chamber step and brass "necking" produced the following response from Mark Rossini:

"Sir –the gun uses a stepped chamber"

This seems to indicate that at a minimum, some PPSs use a stepped chamber, but doesn't indicate whether Walther recently made a switch from tapered to stepped chambers in the PPS line, or why some individuals (Surreal) would have PPSs without the step.

I have a customer service email outstanding with Walther Customer Support as well. I'll post here if anything interesting or informative comes of it.

TiroFijo
08-23-2018, 04:41 PM
Why would anyone want to "extend the time during which the chamber is obturated as the cartridge case is extracted"?

In a normal 9 mm pistol (short recoil, locked breech) the case begins to extract from the chamber well after the bullet has left the muzzle, and the pressure is at a safe level and dropping very rapidly in the bore/chamber at this time.

ArgentFix
08-23-2018, 11:52 PM
I'm out of my depth in this sub, but I coincidentally happened to fire some Winchester 124gr NATO brass through both a SIG P226 (left) Walther P99c AS (right).

29474

The "necking" is hard to capture with my crap skills and cellphone but is slightly visible on the right. It's plainly visible in real life, and brass rounds from my VP9 display the same marks.

I hope this is useful.

Bucky
08-24-2018, 05:13 AM
The gun that this seems evident of to me, is my P2000. Whenever I shoot that gun, I get a pronounce ring mark about 1/3 way down the case. I don’t know if it does anything for velocity, but I’d swear it sure seems to keep the gun cleaner.

olstyn
08-24-2018, 06:08 AM
My full-size P99 has a stepped chamber, but my P99c does not. Based on their date codes, it seems Walther went back to using stepped chambers at some point between 2009 and 2016. I can't speak for what HK chambers do to brass, but the little ring my P99 leaves on brass looks just like the photo ArgentFix posted - it's a very obvious mark, but it could hardly be called "bottlenecked." I doubt you'd even get to a true bottlenecked state even firing the same case a large number of times through a stepped chamber, because the sizing and flaring dies would likely remove any actual bottleneck.

CCT125US
08-24-2018, 07:38 AM
The stepped chambers seem to be more tolerant of ammo variation, while still maintaining accuracy in my opinion. Not a dig on Glock, as the following examples are rounds not to spec. When I was reloading, occasionally an out of spec round (would not pass the case gage) would be produced. I found that even these rounds would pass a plunk test in ny HK 9mms. Not so with the Glocks. I even had some that were slightly over sized at the base (thanks Dillon) that would not feed into the Glock. These Same rounds fed fine into the HK chamber. My thinking is that the chamber on HK 9mm, is oversized, and the step down helps to center the front portion of the case along the centerline of the bore. Just my thoughts.

Jim Watson
08-24-2018, 12:05 PM
I rummaged through my box of mixed brass and found cases with the same GFL (Fiocchi) headstamp that had been fired in other guns. One clearly out of a Glock, the other unknown, it has a soft "crater" like a Beretta leaves but a firing pin wipe through the edge of the crater.

The bottleneck is about .17" long from the case mouth, looks longer than picture above.

The bottleneck is .384" diameter, Glocked case neck is .383+", and the other is .383".

The shoulder is .392" diameter, same location on Glocked case is .389", other is .388".

The body at the pressure ring is .393", same on Glocked case is .390", other is .389".

Necks are within a thou, but the shoulder and body are .003-.004" larger on the bottlenecked empty.
I don't know why, and it isn't much but it is clearly and measurably there.

Yes, I know that is one example of each and I didn't measure to the tenth, but I feel confirmed that there is a slight bottleneck in the chamber, not just a ring in appearance.

MGW
08-24-2018, 01:05 PM
I was always told it was to assist with extraction if the actual extractor was broken. Maybe that was an old wives tale though.

Trooper224
08-24-2018, 01:41 PM
My Walther PPQ had a stepped chamber. According to Walther this was to increase accuracy and help prevent chamber fouling. The gun was very accurate for a polymer gun and the chamber stayed fairly clean. Whether the stepped chambered actually aided in this I can't say. It was far more sensitive to handloads and made proper sizing even more critical than usual. In the end, I really didn't see it as a plus.

Talionis
08-24-2018, 01:50 PM
Don't take this as official word from HK or anything. But in my own experience the stepped chamber is fantastic for both accuracy and reliability. Since I started shooting VP9's, I've stopped case gauging my ammo, even for major matches. There just isn't a point in the wasted time for me anymore. With the stepped chamber, they will feed even significantly out of spec reloads, and each of them is capable of sub 2" groups at 25 yards when I don't suck.

TGS
08-24-2018, 03:36 PM
I was always told it was to assist with extraction if the actual extractor was broken. Maybe that was an old wives tale though.

Sounds like someone is conflating stepped chambers with fluted chambers....in which case it's absolutely true. Fluted chambers have an effect of floating the cartridge, which is necessary for guns that open too soon. They were standard on HK roller-delayed rifles, as well as the HK P7.

farscott
08-24-2018, 03:49 PM
Sounds like someone is conflating stepped chambers with fluted chambers....in which case it's absolutely true. Fluted chambers have an effect of floating the cartridge, which is necessary for guns that open too soon. They were standard on HK roller-delayed rifles, as well as the HK P7.

Fluted chambers are famous for leaving streaks of soot on the fired brass, and the brass is quite recognizably marked. I did learn that at least one P7M8 will function just fine without an extractor as one of my did so.