M1928A1 Extractors Can Lose Their "flex"

[reconbob]

I had mentioned this before but now I have much more data to go on.

I have built over 50 guns now using the standard "Russian" parts sets.

I would say 25% (maybe a little more) of the time the extractors in the

bolts have lost their springyness or "flex" from sitting in a bolt in the

flexed position for 70+ years.

When you try to use a bolt that has a set extractor, the extractor

it will not be able

to flex away from the bolt when the front angled surface of the extractor

hits the rim of the cartridge and snap down into the rim. The extractor

just hits the cartridge without "grabbing" it. The gun will not fire and of

course the extractor will not extract the cartridge.

I first noticed this when we would assemble guns and the bolt would

not completely shut when you went to test cycle it with dummy cartridges.

Or, it would take excessive force to slam the bolt shut so the extractor

would grab the cartridge. I have also had guns in for repair where all

sorts of serious problems were imagined that all went away with a

new extractor.

The fix is easy - use an extractor that still has its "flex" or better yet

a spare extractor that has not been flexed in a bolt for 70 years.

The moral of the story is - if you have a spare parts set or bolt do

not assume that your almost new spare bolt is ready to go. It might have

a set extractor.

To check this is easy. Field strip the gun and remove the firing pin

assy and hammer and hammer pin from the bolt. Reassemble the bolt,

H-lock, and actuator into the receiver as you normally would. Now seat

a fired case in the chamber and sharply slide the bolt shut using the

actuator knob as a handle. The bolt should easily shut and the extractor

should pull the cartridge out. If you have to slam the bolt to get it to work

or if the bolt just won't pick up the case you have a set extractor.

So far I have not been able to tell the difference between a set extractor

and one that is ok when you compare them side by side when they are

removed from the bolts.

 

Bob

[jim c 351]

Bob,

Did you notice if the problem extractors were Savage, Stevens or both??

Is it possible they were incorrectly heat treated at manufacture ??

Would it not be possible to retemper the problem extractors??

Jim C

[reconbob]

I don't think I have seen an extractor that was not marked with the square S.

I don't know about heat treatment. Since new extractors are still inexpensive and

available there is not much incentive to get into heat treat...

 

Bob

[mnshooter]

I had mentioned this before but now I have much more data to go on.

I have built over 50 guns now using the standard "Russian" parts sets.

I would say 25% (maybe a little more) of the time the extractors in the

bolts have lost their springyness or "flex" from sitting in a bolt in the

flexed position for 70+ years.

When you try to use a bolt that has a set extractor, the extractor

it will not be able

to flex away from the bolt when the front angled surface of the extractor

hits the rim of the cartridge and snap down into the rim. The extractor

just hits the cartridge without "grabbing" it. The gun will not fire and of

course the extractor will not extract the cartridge.

I first noticed this when we would assemble guns and the bolt would

not completely shut when you went to test cycle it with dummy cartridges.

Or, it would take excessive force to slam the bolt shut so the extractor

would grab the cartridge. I have also had guns in for repair where all

sorts of serious problems were imagined that all went away with a

new extractor.

The fix is easy - use an extractor that still has its "flex" or better yet

a spare extractor that has not been flexed in a bolt for 70 years.

The moral of the story is - if you have a spare parts set or bolt do

not assume that your almost new spare bolt is ready to go. It might have

a set extractor.

To check this is easy. Field strip the gun and remove the firing pin

assy and hammer and hammer pin from the bolt. Reassemble the bolt,

H-lock, and actuator into the receiver as you normally would. Now seat

a fired case in the chamber and sharply slide the bolt shut using the

actuator knob as a handle. The bolt should easily shut and the extractor

should pull the cartridge out. If you have to slam the bolt to get it to work

or if the bolt just won't pick up the case you have a set extractor.

So far I have not been able to tell the difference between a set extractor

and one that is ok when you compare them side by side when they are

removed from the bolts.

 

Bob

 

More great information. I hope this gets added to the pinned section.

[dalbert]

 

More great information. I hope this gets added to the pinned section.

 

mnshooter and reconbob,

 

I just added a link to this thread in the pinned reference post at the top of the page.

 

Thanks!

 

David Albert

dalbert@sturmgewehr.com

[Bridgeport28A1]

I would think stripping a dummy round out of a magazine and than seeing if it will extract the round from the chamber would be the preferred check of the extractor.

 

Every LE armorer course I attended alway discouraged loading a auto-loading pistol/shotgun by dropping as round in the chamber and than allowing the slide/bolt to close which causes the extractor to have to jump over the cartridge rim. This was described as being "hard on the extractor".

 

YMMV

 

Ross

[mnshooter]

Definitely in the case of 1911s , mauser 98s, and other "controlled feed" systems, there is more demanded of the extractor if it has to jump over a case rim, as that is not how it usually works in normal operation. How many thousands of first loaded rounds have actually been fired in 1911's in this manner is anyone's guess, but this method of loading has been in print many times.

A Thompson bolt pushes the round out of the magazine, in front of the extractor, and then forces the extractor to jump over the case rim just before ignition. Except for any reduction in bolt momentum from the feeding action, the mechanics of the extractor operation are the same in both magazine fed and single loaded instances.

Edited October 18, 2012 by mnshooter

[reconbob]

Yes, feeding the cartridge out of the magazine on a Thompson does not

"help" the extractor. When autoloading pistols, magazine fed shotguns, and

many bolt action rifles feed, the base of the cartridge slides up under the extractor

and the extractor is not forced to snap over the rim.

The Thompson has feed lips which prevent the base of the cartridge from

sliding up and under the extractor so the extractor is forced (by design) to

snap over the rim when the cartridge seats in the chamber.

I will add, that if you ever run into this, the difference between a set extractor

and a good one is like night and day. A good extractor will easily snap over the

rim of the cartridge.

 

Bob

[TSMGguy]

Next we'll again be seeing someone advising not leaving magazines loaded for long periods of time to avoid a "set" in the magazine spring or, worse yet, advising that magazines (or bolts) be stored disassembled, completely removing any force from the springs at all. As intuitively appealing as these ideas might be, they are false. There are no formulas in materiels engineering that describe or predict a "set" (with corresponding reduction in performance) taken by properly designed and constructed springs due to long term compression or tension within the design range.

 

Can a spring be deformed or even destroyed by stretching it outside of its design limits? Of course. So, far more likely, these extractors were simply bent too far during installation or removal. We all remember being cautioned against lifting the extractor farther away from the bolt body than is necessary for these operations. This is why.

 

A TSMG's extractor is designed to "snap over the rim". This is not a design flaw. The cartridge is initially stripped from the magazine and pushed toward the chamber by the lower edge of the bolt. There is no controlled feed situation where the extractor engages the cartridge rim through the entire feed cycle such as we see with the 98k or even the Winchester 9422. Will original extractors wear because of this design feature? Of course, but they'll last for quite a while, too!

Edited October 18, 2012 by TSMGguy

[reconbob]

This is not intuition. I am dealing with facts. I have a special knowledge of this from

building over 50 guns using 50 different parts sets. The bolts don't work. You replace

the extractor and then they work. This is an example of something that was not

anticipated - no one thought of leaving extractors in bolts for 70+ years.

I know the question of ruining mag springs by leaving magazines loaded has been

argued an re-argued for as long as there have been magazines.

If you loaded 100 magazines, and left them for 70 years and later found that

28 of them did not work, and replaced the springs with new springs and they all worked

you would conclude that the springs had been damaged, right? No wait - YOU would

say that those springs just happened to be bad ones.

If you over-flex the extractor during assy or disassembly it would be weaker and

snap over the cartridge more easily, not become so stiff it would not flex over the rim

at all.

So poke fun all you want about storing guns disassembled. This is a legitimate

problem that is easy to check for and easy to fix. When I get to 100 guns I'll give you

an update...

 

Bob

Edited October 18, 2012 by reconbob

[darrylta]

Amen Bob,

Darryl

 

 

 

 

 

http://i897.photobucket.com/albums/ac178/DLRegister/Untitled1.jpg

Edited October 18, 2012 by darrylta

[rjb1]

With all due respect to Bob, and that is an awful lot of respect, TSMGGuy is right about this.

 

There is no (known) property of materials under stress that would cause them to lose their "flex". There may well be a problem with some of the extractors in old parts sets, and Bob may have found it, but it's not due to their time duration in a stressed state.

 

If there is such a time-dependent term in the stress-strain relations equations it needs to be discovered and documented and the text books re-written.

(The only exceptions are creep over time at high temperatures and short-duration events such as shock or impact loading.)

 

This isn't a matter of sarcasm or poking fun (at anyone). If there is a time-dependency, it isn't part of the body of current engineering knowledge. (At least none of my engineering colleagues are aware of it and I can't find it in any of the several engineering machine-design texts that I have consulted.)

 

A Problem with extractors: Yes, certainly...

 

The Cause due to "age": Much more uncertain... more information/experimentation needed...

 

In my own case, I have been doing engineering-research for several decades for NASA, DARPA, H-P, and etc. In the course of that time, we have on more than one occasion came up with results that seemed to to violate the known laws of physics. On those occasions someone would usually say, "Well, we can either: a) go directly to Stockholm and pick up our Nobel Prize for discovering this exception to the known Laws of Physics or figure out what we did wrong." So far the answer has always been .

[darrylta]

My country boy information/ experimentation has shown me that my old muscle cars set a little lower and rolls a little

bit more in the corners than they did when they were new and my valve springs are a little tired and don't allow me

to get the crisp high revs it once did.

 

It's just common horse sense to not long term store springs in a compressed state and expect it to not be affected?

 

BTW,,I've always thought that the extractor while in the bolt was in a somewhat relaxed state?

 

It's great to learn something everyday.

 

-Darryl

[emmagee1917]

It is not being compressed nor being relaxed that wear them out , it is the cycle of one to the other ( usage ) that does it .

Chris

[rjb1]

Static loading (constant force) is not equivalent to, nor is it calculated the same as fatigue loading (multiple force cycles), as in a spring.

 

The loss of strength as a function of the number of cycles of loading is a well known phenomenon. As an example, for a particular steel, the strength at 100,000 cycles of loading is about 20% less than at 10,000 cycles. It doesn't "level out" (become constant) until ~2,000,000 cycles. The point at which the strength levels out is known as the "endurance limit".

 

Can't compare apples and oranges...

[reconbob]

Honestly, I am lost with this heavy dose of engineering babble. I have to

make guns that work, and fix guns that don't. When these guns were manufactured

they were test and proof fiired and worked and functioned properly. Now, 70 years

later 25+% don't work - an astonishing percentage of failure that would never be allowed

at the time of manufacture. The problem is fixed/corrected by replacing an extractor

(you've seen these kits - most appear unfired) that has been sitting in a bolt with a new

extractor that has not.

So you can pull out the textbooks and pontificate on how engineering theory dictates

that springs don't go bad...and I will replace the extractors that went bad with new extractors

so the guns work.

And there is balance in the universe....

 

Bob

[timkel]

Well I think I'll get a spare extractor just In case.

[Gio]

Amen Bob

 

Frank

[emmagee1917]

Ahhhhh....but how to tell if the new spare extractor is a new one never installed or a new one just removed from a 70 yr old new bolt ?

Chris

[rjb1]

Fine - no more babbling or pontificating. My apologies for doing that.

[ken51]

After seeing this thread yesterday I dug out my bolt from the lend-lease parts kit I got earlier this year. I used the parts kit for a display gun with one of Bob's 80% recievers so the bolt was in the same condition as when I got it. To my surprise when I tried to manipulate the extractor it would not move. With some more effort I was able to get it to move, but it was very stiff. When I removed the extractor I found that it had been glued in place by whatever lubricant they had used that had dried and turned to something like varnish. After a good cleaning it seems to work fine.

 

I don't know if this is what Bob could have run into, but I am certain that my bolt in its original condition would have caused a malfunction. Unfortunetly without a functioning gun I have no way to test the extractor now to see if it would function properly. No answers, just more questions.

 

Ken

[Bridgeport28A1]

I also took my 1928A1 out of the safe and performed Bob's check of the extractor. I had put a Omega parts kit bright bolt that I put a PK '21 modified actuator and PK 28/21 buffer in.

 

My "parts kit" bolt extractor did not extract, everything Bob said was 100% correct!

 

I could not find any visual difference between the "kit bolts" extractor and my square "S" Stevens spares. My extractor was actually fairly clean but had some wear I would attribute to not being a unused extractor. I am thinking those "Russian" parts kits were either used by some one at some point or were from re-furbished Thompson parts during the war.

 

The "bad" extractor appears to be a "S" Savage made extractor and it has an additional mark that none of my square "S" stevens extractors have. It almost appears to be a "2"

 

Bad extractor pics

http://i1098.photobucket.com/albums/g374/TW56/Thompson%20extractor%20bad%20one%20from%20kit%20bright%20bolt/IMG_7009.jpghttp://i1098.photobucket.com/albums/g374/TW56/Thompson%20extractor%20bad%20one%20from%20kit%20bright%20bolt/IMG_7011.jpghttp://i1098.photobucket.com/albums/g374/TW56/Thompson%20extractor%20bad%20one%20from%20kit%20bright%20bolt/IMG_7012.jpg

 

I want to thanks Bob for saving me from having a "single shot" Thompson SMG next range trip. That would have been slightly embarrassing.

 

Ross

Edited October 23, 2012 by Bridgeport28A1

[Big Al]

I have a thought on the matter. Maybe the extractors were over-flexed when the guns were disassembled to clean off the cosmoline prior to being made into parts kits. Just a WAG.

[buzz]

1. Engineering isn't babble. It's the exact opposite of babble.

 

Engineering is the practical application of knowledge to build and maintain stuff. That's it, nothing more and nothing less.

 

The operative word there is "knowledge".

 

Knowledge comes from testing and measurement.

 

Engineering is not an episode of Sally Jessie Raphael where everyone screeches their emotional opinion back and forth.

 

 

2. Spring "set" or "creep" is a well known physical phenomenon.

 

Every mechanical and civil engineer on earth knows what strain relaxation is, but for some reason 50% of gun guys say it doesn't exist.

 

It's really weird to have a large number of people denying the existence of something so well documented.

 

Just type "strain relaxation" or "spring creep" into google and you can read all about it from 100,000 different scientific sources and design guides.

 

If you hang a weight from a spring and it stretches the spring to 20 inches long, when you come back in 30 years the spring will be 21 inches long.

 

The effect becomes greater with high load, high temperature, or the long duration.

Edited October 11, 2014 by buzz

[buzz]

Here's a link to an explanation of the difference between spring creep and spring fatigue.

 

This company has been making springs since 1852.

 

http://www.lesjoforsab.com/technical-information/durability.asp

 

From their website:

 

"One physical phenomenon with metals is that at stress below the yield strength of the material, a very slow plastic deformation takes place. In the spring branch this is called creep, when a spring under constant load looses length and it is called relaxation when a spring under constant compression loses load."

 

 

Here's the wikipedia entry on the subject, it's actually a very good write up.

 

http://en.wikipedia.org/wiki/Creep_(deformation)

 

cut and paste the whole line above into your browser, it's not hotlinking correctly if you just click on it

Edited October 11, 2014 by buzz