Scorpion Extractor Spring Modification

[romukom]

As we all know, CZ designed the Sorpion to function as reliable as it can be for military and law enforcement. 
I decided to start a new thread as continuation of thread of dented cases. 
http://www.czfirearms.us/index.php?topic=88580.0
As  mentioned the dented cases is the result of the cases hitting a specific corner of the bolt as it gets ejected from the bolt.  I believe that CZ purposely designed the bolt to include a build-in case deflector were the cases are ejected in the 2 to 3 o?clock instead of 4 to 5 o?clock seen in semi automatic pistols. 

It was noticed that the hotter the load, the dents are more prominent.  Also, it was noticed that the case rim gets more gouged than normal. 
I had a theory that because of the heavy extractor spring, the case is held tighter. And when the case gets ejected, it will hit harder to the ?bolt deflector?.  By reducing the force of the extractor spring it should result with less dented cases.

Of course, the main reason of modification was save the case rims from being worn out from normal as a reloader.  Granted, 9mm once fire cases are cheap right now but I have some problem feeding the Scorpion fired cases to the shell plate on my reloading press

To remove extractor, push the extractor pin from the bottom of the bolt.



I found a spring that can be use to substitute the stock extractor spring.  It is 3/16? in diameter and 39/64? long and 0.026? wire diameter.
http://www.homedepot.com/p/Everbilt-Spring-Assortment-Kit-84-Pack-13554/203133714

The first thing is to find out what is the poundage of the stock extractor spring.  Luckly, at the office we have a force gauge.  At full compression it is about 15 lbs.  At ?? compression to simulate how much I have to push the extractor during install is about 8 lbs.

 
 

With the spring from Home Depot kit, the gauge read 7 lbs at full compression.  Unfortunately, I was not able to have reading at ?? compression since the gauge is rated from 6 to 60 lbs.  I estimate it is about 5 lbs.


Here is the extractor spring (top)  vs HD spring.  As you seen it is about 3/16? shorter.  So it occurred to me to make a guide rod out of 3mm socket hex cap screw that I have around.  I used a screw that is not fully threaded. 


Unfortunately, the head diameter is larger than the spring cavity.   I chuck it into my drill and with a bastard file and reduce the diameter by spinning the drill.

Once file the head enough to fit the cavity, the screw was cut with a hack saw while still in the chuck.



Hd spring vs spring guide vs m3 socket hex cap screw.


Installing the guide rod and spring.



As I finished installing the HD spring, I noticed that the case are held less tightly compared with the stock extractor spring.  I cycled the bolt with snap caps and dummy rounds and noticed that rounds were ejected at 4 o?clock. 

Fast forward today,  I had the chance to test my carbine with the spring from home depot and homemade guide rod.  Unfortunately I only had a short range time so I was able to burn 80 rounds.  I used 30 rounds of my reloads (6.2 grn of AA#7, extreme FP 124 grns, 1.060 OAL),  20 rounds of factory ZQI 124 grns RN, and  30 rounds of 124 grns factory Herters.
All the rounds were ejected without any problems.  I was doing mostly double taps as the indoor range I went does not allows rapid fire.

Here are the spent cases that were randomly selected.  And to my surprise my theory was validated.  With a softer spring, the case dents were less prominent.  Also the ejector indentations were less prominent as well.
Look at the reloaded case; see the two ejector indentation. This one was fired before by my scorpion.   Overall, I am happy with the result.  I will see what happens long term.  In any case, I hope that this thread will help for those who owns a Scorpion and reloads as well.
Edit: to correct some misspelling and grammar



Cartridege rims and dents

[akuser47]

Great work thanks for sharing.

[HBi]

Awesome post romukom! We have actually been making and testing different extractor springs too, still trying to figure out why they are so stiff from the factory. Think you nailed it though. Maybe a combination between shell deflection in tight quarters and wider range of bolt velocities due to direct blowback?

Or, maybe S&B paid someone off at CZ-UB :-) some of those dented cases are impossible to reload!

Either way, your solution and making that guide from a cap head screw is very clever! Well done!

[romukom]

Yeah trying to figure out what is going on was the fun part.  Also, it sort of helps when you can visualize things in your head and have the evidence to confirm that. I agree, it has to do with the blowback design. 
This is why I used the same ammo I had when I first took my carbine at the range.  These were the same batch with the the exception of my reloads but it was the same load data.

One thing that made me look closely at the design of the bolt was after I watched the  video of the Bren 805 from mrgunsngear. He was shooting his FDE Bren. And the video was in slow motion. Because the case deflector is black and his rifle is FDE, it was clear to see what is going on.  As we all know, there is no external case deflector in the scorpion.
Anyways I hope that you will come out with a better sourced spring. I feel that the one I am using from home depot will not perform well long term.

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[biggerhammer]

Nice work but I personally prefer the stronger factory spring, I don't reload 9mm so reliability is my main focus. With the stronger spring, I don't need to worry about a little powder residue or grit causing my extractor to get stuck in the open position. That strong ass spring is going to keep my extractor right where it needs to be.

[romukom]

Yep, there is no doubt where reliability was the main focus.

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[Torked]

Such an awesome very detailed document on a fix. You sir are AWESOME!

[SouthernScorp]

I reload, and the dented mouths aren't really a problem but the extra strong extractor really does chew the hell out of the rims like the OP said. HBI are you going to be releasing a spring kit ? your trigger springs are a must have item and these extractor springs or kits would be a big +1 to us reloaders

[romukom]

Yeah, how about a 3 spring kit. Reloader (light weight), all around (medium), and self defense (heavy).  Last but not least, reliability (stock spring)

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