Breech Block Failure 1916/1920 Erfurt

Green57 · 01-29-2021, 05:09 AM

gunbugs,

I think you might be on to something with this statment "Abnormally large diameter rims on the cartridge?"

I have a S&W model 1917 that shoots .45 ACP utlizing moon clips. Normally I shot WWB or RGB ammo out of it. Went shooting one day and Wally world was out of the normal ammo so I bought some Blazer brass.

It was noticablly harder to snap this ammo into the moon clips, to the point that I decided it was not worth the effort. The only reason I could think of that would make the Blaser harder to load into the clips was if the extractor groove diameter was at the upper limits. It did shot fine through my Colt WWI reissue though.

I wonder if the Blazer 9mm cases are manufactured towards the upper limits like their .45 is? Might be worth breaking out the calipers to measure the groove and rim diameters on the case to find out if this could have been a contributing factor to the BB failure.

G57

G.T. · 01-29-2021, 08:08 AM

When a primer is pierced, the rapid occurrence of breechblock damage is from one thing only, and that is escaping high pressure gas going back, and going up! One has to remember, the breech is locked during the first few milliseconds after firing. The only mechanical movement is inertially back, with the complete top end involved, the damage is most likely done before the receiver ever even starts to move... I have seen this progression to failure with my own eyes, and three shots is about the max you get... correct the headspace issue, and the problem goes away! I am so paranoid about this that I always make sure the toggle train closes tight on the "GO" gauge, (yes, you need both gauges!) when installing new or old original barrels. Excessive head spacing can be a result, or combination of the following. Breechblock at one end or the other in tolerance, barrel chambered too deep, wear on any or all of the three main toggle train pins. It adds up fast! Good luck to all when shooting a loose gun!

... best to all, til.....lat'r....GT...

gunbugs · 01-29-2021, 08:23 AM

I understand the operation on the locking/unlocking system on the Luger, and other firearms. However, the O.P. states that no pierced primers were evident in this occurrence. So, that being said, why would the extractor beat its way through the top of the block? Even with a couple thousandths excessive headspace, the cartridge should obturate, and seal the chamber from gas leakage. I deal with firearms that have excessive headspace on a fairly common basis, and the typical symptom is stretched brass, not gas leakage. Even a pierced primer should not leak enough gas to make an extractor try to leave the gun. Again, the O.P. states no pierced primer here.

01-29-2021, 08:08 AM	#2
G.T. Lifer Lifetime Forum Patron Join Date: Jun 2002 Location: Chandler Arizona Posts: 3,541 Thanks: 1,342 Thanked 3,743 Times in 1,020 Posts	breaking the block! When a primer is pierced, the rapid occurrence of breechblock damage is from one thing only, and that is escaping high pressure gas going back, and going up! One has to remember, the breech is locked during the first few milliseconds after firing. The only mechanical movement is inertially back, with the complete top end involved, the damage is most likely done before the receiver ever even starts to move... I have seen this progression to failure with my own eyes, and three shots is about the max you get... correct the headspace issue, and the problem goes away! I am so paranoid about this that I always make sure the toggle train closes tight on the "GO" gauge, (yes, you need both gauges!) when installing new or old original barrels. Excessive head spacing can be a result, or combination of the following. Breechblock at one end or the other in tolerance, barrel chambered too deep, wear on any or all of the three main toggle train pins. It adds up fast! Good luck to all when shooting a loose gun! ... best to all, til.....lat'r....GT...

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01-29-2021, 05:09 AM	#1
Green57 User Join Date: Jan 2006 Posts: 32 Thanks: 0 Thanked 3 Times in 3 Posts	gunbugs, I think you might be on to something with this statment "Abnormally large diameter rims on the cartridge?" I have a S&W model 1917 that shoots .45 ACP utlizing moon clips. Normally I shot WWB or RGB ammo out of it. Went shooting one day and Wally world was out of the normal ammo so I bought some Blazer brass. It was noticablly harder to snap this ammo into the moon clips, to the point that I decided it was not worth the effort. The only reason I could think of that would make the Blaser harder to load into the clips was if the extractor groove diameter was at the upper limits. It did shot fine through my Colt WWI reissue though. I wonder if the Blazer 9mm cases are manufactured towards the upper limits like their .45 is? Might be worth breaking out the calipers to measure the groove and rim diameters on the case to find out if this could have been a contributing factor to the BB failure. G57

01-29-2021, 08:23 AM	#3
gunbugs Lifetime Forum Patron Join Date: Sep 2013 Location: Fairbanks, Alaska. Home of the best moose. Posts: 683 Thanks: 375 Thanked 1,228 Times in 415 Posts	I understand the operation on the locking/unlocking system on the Luger, and other firearms. However, the O.P. states that no pierced primers were evident in this occurrence. So, that being said, why would the extractor beat its way through the top of the block? Even with a couple thousandths excessive headspace, the cartridge should obturate, and seal the chamber from gas leakage. I deal with firearms that have excessive headspace on a fairly common basis, and the typical symptom is stretched brass, not gas leakage. Even a pierced primer should not leak enough gas to make an extractor try to leave the gun. Again, the O.P. states no pierced primer here.