Case Discoloration Comparison

TunnelRat · August 19, 2014, 01:57 PM

Hi all,
Two weekends ago I was shooting a new M&P 9mm Compact next to an HK P2000. Both in 9mm, both firing 115 gr Blazer Brass from the same case lot (I am not making any claims that Blazer Brass is somehow a Gold Standard for ammo). What I noticed was that the cases from the HK P2000 were being ejected noticeably cleaner than those from the S&W M&P. Both guns were cleaned prior to the shooting. Essentially it looked like gases were escaping passed the edge of the casing (towards the bottom where the feed ramp is) and causing the discoloration of the brass on the M&P. After 100 rounds through each pistol, the M&P was also noticeably dirtier than the P2000 on the feedramp and around the mouth of the chamber.

Could this be a result of the HK's stepped chamber allowing a tighter gas seal? Any thoughts?

S&W on the left, H&K on the right.

Thanks,
-TR

Venom1956 · August 19, 2014, 02:08 PM

I would bet thats a good guess. the Hk cases look noticeably smaller at the front and seem to have an mark around the case where the step would be.

Sevens · August 19, 2014, 02:14 PM

You wanna see some wacky brass? Find some that was launched from a gun with a fluted chamber!

James K · August 19, 2014, 03:16 PM

IMHO, you have a combination of a somewhat oversize chamber on the M&P an a tight one on the HK. The result is usually somewhere in the middle, but here there is a sharp contrast.

FWIW, a fellow named Georg Luger designed the chamber for his 9mm pistol with a step exactly the same way and because he thought it gave better obturation. The pistols were made with stepped chambers until WWII, when the chambers were made without the step to speed production. Looks like old Georg had something.

Jim

TunnelRat · August 19, 2014, 03:30 PM

Quote:

IMHO, you have a combination of a somewhat oversize chamber on the M&P an a tight one on the HK. The result is usually somewhere in the middle, but here there is a sharp contrast.

Sounds reasonable. The brass from the P2000 almost looks new, though as Venom pointed out you can see the line from the stepped chamber and the slight difference in case bulging at that point.

One thing worth noting, is that while I would agree the P2000 has a tighter chamber, for some reason it feed snap caps that are beat up that the M&P chokes on. Frankly those snap caps are now out of spec and I don't blame the M&P for not feeding them, but it is interesting.

Quote:

FWIW, a fellow named Georg Luger designed the chamber for his 9mm pistol with a step exactly the same way and because he thought it gave better obturation. The pistols were made with stepped chambers until WWII, when the chambers were made without the step to speed production. Looks like old Georg had something.

What silly guy that Luger, naming himself after a pistol.

AK103K · August 19, 2014, 04:52 PM

Quote:

You wanna see some wacky brass? Find some that was launched from a gun with a fluted chamber!

I was gonna say. My HK brass was always a lot dirtier than anything else Ive shot, pistol or rifle calibers.

Is that line about a quarter of the way down from the mouth on the HK brass, the "step"? It seems just forward of it, the brass is showing a little color.

TunnelRat · August 19, 2014, 06:16 PM

Quote:

Is that line about a quarter of the way down from the mouth on the HK brass, the "step"? It seems just forward of it, the brass is showing a little color.

I believe so.

James K · August 20, 2014, 07:51 PM

When a gun is fired, one of the first things the pressure does is to expand the thin case neck to release the bullet and seal off the chamber. That puts almost the full power of the gas behind the bullet and keeps gas carbon from dirtying the chamber and the brass. But that sealing, called obturation, takes an instant to complete and in that instant some gas and dirt can leak backward. How much depends on several factors. Generally, the less pressure, the less obturation and the more blackening of the case. Other factors, like chamber size and the flexibility of the case can also be factors.

Since all the examples shown were from the same ammo lot from the same maker, I would have to assume that the difference here is in the chamber, not the ammunition.

Jim

rock185 · August 23, 2014, 02:31 PM

James K, Thanks for that info. I thought I was pretty knowledgeable about most things 9MM, but did not know about the step in the earliest 9MM chambers.

RX-79G · August 23, 2014, 02:45 PM

Quote:

FWIW, a fellow named Georg Luger designed the chamber for his 9mm pistol with a step exactly the same way and because he thought it gave better obturation. The pistols were made with stepped chambers until WWII, when the chambers were made without the step to speed production. Looks like old Georg had something.

My understanding was that the tapered chambers are actually a little harder to machine, but that the stepped chambers were causing problems with the wartime steel cased 9mm ammo.

**JohnKSa** · August 23, 2014, 02:49 PM

The S&W is a compact and therefore it may begin the extraction process a tiny bit sooner than the P2000. That can make a difference in how much the gun fouls in the chamber area.

RX-79G · August 23, 2014, 03:33 PM

It's only a difference of .16" in barrel length.

But the M&P's action design may unlock earlier in the cycle than HK, with more residual chamber pressure.

Big Shrek · August 23, 2014, 11:47 PM

I was thinking that there may have been a little oil left in the chamber of the S&W as well...

tends to glom burnt powder in the chamber...giving the brass a funny look...

August 19, 2014, 01:57 PM	#1
TunnelRat Senior Member Join Date: May 22, 2011 Posts: 12,212	Case Discoloration Comparison Hi all, Two weekends ago I was shooting a new M&P 9mm Compact next to an HK P2000. Both in 9mm, both firing 115 gr Blazer Brass from the same case lot (I am not making any claims that Blazer Brass is somehow a Gold Standard for ammo). What I noticed was that the cases from the HK P2000 were being ejected noticeably cleaner than those from the S&W M&P. Both guns were cleaned prior to the shooting. Essentially it looked like gases were escaping passed the edge of the casing (towards the bottom where the feed ramp is) and causing the discoloration of the brass on the M&P. After 100 rounds through each pistol, the M&P was also noticeably dirtier than the P2000 on the feedramp and around the mouth of the chamber. Could this be a result of the HK's stepped chamber allowing a tighter gas seal? Any thoughts? S&W on the left, H&K on the right. Thanks, -TR __________________ Know the status of your weapon Keep your muzzle oriented so that no one will be hurt if the firearm discharges Keep your finger off the trigger until you have an adequate sight picture Maintain situational awareness

August 19, 2014, 02:08 PM	#2
Venom1956 Senior Member Join Date: October 4, 2008 Location: WI Posts: 3,656	I would bet thats a good guess. the Hk cases look noticeably smaller at the front and seem to have an mark around the case where the step would be. __________________ E-Shock rounds are engineered to expend maximum energy into soft targets, turning the density mass into an expanding rotational cone of NyTrilium matrix particles, causing neurological collapse to the central nervous system.- Yeah I can do that. I guarantee you will know it if a bicyclist hits your house going 1000 mph. -Smaug

August 19, 2014, 02:14 PM	#3
Sevens Senior Member Join Date: July 28, 2007 Location: Ohio Posts: 11,756	You wanna see some wacky brass? Find some that was launched from a gun with a fluted chamber! __________________ *Attention Brass rats and other reloaders:* I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.

August 23, 2014, 02:31 PM	#9
rock185 Senior Member Join Date: September 2, 2001 Location: Out West in Rim Country Posts: 1,093	James K, Thanks for that info. I thought I was pretty knowledgeable about most things 9MM, but did not know about the step in the earliest 9MM chambers. __________________ COTEP 640, NRA Life

August 23, 2014, 02:49 PM	#11
JohnKSa Staff Join Date: February 12, 2001 Location: DFW Area Posts: 24,990	The S&W is a compact and therefore it may begin the extraction process a tiny bit sooner than the P2000. That can make a difference in how much the gun fouls in the chamber area. __________________ Do you know about the TEXAS State Rifle Association?

August 19, 2014, 03:16 PM	#4
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	IMHO, you have a combination of a somewhat oversize chamber on the M&P an a tight one on the HK. The result is usually somewhere in the middle, but here there is a sharp contrast. FWIW, a fellow named Georg Luger designed the chamber for his 9mm pistol with a step exactly the same way and because he thought it gave better obturation. The pistols were made with stepped chambers until WWII, when the chambers were made without the step to speed production. Looks like old Georg had something. Jim

August 20, 2014, 07:51 PM	#8
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	When a gun is fired, one of the first things the pressure does is to expand the thin case neck to release the bullet and seal off the chamber. That puts almost the full power of the gas behind the bullet and keeps gas carbon from dirtying the chamber and the brass. But that sealing, called obturation, takes an instant to complete and in that instant some gas and dirt can leak backward. How much depends on several factors. Generally, the less pressure, the less obturation and the more blackening of the case. Other factors, like chamber size and the flexibility of the case can also be factors. Since all the examples shown were from the same ammo lot from the same maker, I would have to assume that the difference here is in the chamber, not the ammunition. Jim

August 23, 2014, 03:33 PM	#12
RX-79G Junior member Join Date: October 27, 2013 Posts: 1,139	It's only a difference of .16" in barrel length. But the M&P's action design may unlock earlier in the cycle than HK, with more residual chamber pressure.

August 23, 2014, 11:47 PM	#13
Big Shrek Senior Member Join Date: August 6, 2009 Location: NorthWest Florida Posts: 1,358	I was thinking that there may have been a little oil left in the chamber of the S&W as well... tends to glom burnt powder in the chamber...giving the brass a funny look... __________________ Marlin Specialist Calico Specialist A gun should be a tool in the hands of a deadly weapon, not a deadly weapon in the hands of a tool.