Closed bolt internal "contours"

[Jones]

Closed bolt, semi-auto having some ejection problems. For what it's worth; I'm using a SMG extractor for better rim engagement / extraction.

Inside the bolt is the barrel / feed ramp clearance cut and above it, a sloping face.
When firing, the brass is more or less just tumbling out. Hot ammo and the empties end up about 6 to 8 feet away, lighter ammo and they practically end up in my pants cuff.
Other times it's stove-piped empties and on three occasions, jammed the empty so tight between bolt and magazine well that I've had to remove the top cover and lift the nose of the bolt to get it to let go of the brass.
As you can see in the first picture, the brass is hitting the border line between clearance cut and the sloped face above it then bouncing off the slope.

The machinist in me wonders why the bolt's sloping inner face isn't machined so the the bottom of the slope blends in with the radius of the clearance cut.
I'm tempted to re-machine the internal configuration to get rid of that ridge. See second picture.
I don't want to remove so much weight so that the lighter bolt cycles so fast that feeding is adversely affected although I hear that some of the closed bolt minis are capable of 1,200 maybe 1,600 rpm and that means their bolts are moving pretty darned fast.
I don't want to re-engineer the UZI but would like this thing to be a little more reliable.
I'm just not quite satisfied with "Ya know, 60% of the time, this works 100% of the time."

https://ibb.co/86nhbQX
https://ibb.co/zRBCpNH

 

[kanewtervalve]

If you dig in the Library here you will see how full auto extractors are modified for semi use, it also explains why.

 

[Jones]

Thanks for the library suggestion regarding the extractors. Unless I missed something, it sounds like the SA extractors aren't good for FA use but the FA extractors are OK in semis.
I buffed mine with a Cratex point in my Dremel tool and now have full contact with the cartridge rim while maintaining a .0005 to .0015" tip clearance at the deepest point of the rim recess.

 

[kanewtervalve]

If you notice the SA extractor is modified slightly, this is not to say that FA won't work in them but both of mine have an diagonal cut at one end for a more
positive catch on the rim. This is usually if you are having issue with the FA in a SA.
Check this thread: http://www.uzitalk.com/forums/showthread.php?48734-Extractor-difference-semi-full-UZI

 

[Jones]

That covers my extractor question. But the work on the bolt interior to get rid of or at least blend the barrel clearance cut radius in with the sloping face (back face of ejection port in bolt) still remains to be sorted out.

 

[kanewtervalve]

I would try the modified extractor first and your bolt may be a non issue.

 

[Jones]

Gonna do just that.
I looked close at my extractor and was not impressed with the contact point(s)-- or lack thereof. The edge of the hook is straight across so the case rim is only caught through the center of the rim arc. With a Cratex point in my Dremel tool I got a concave edge on the hook so that it settles in and grabs more of the rim. Also tweaked the tension for a better grip on the case rim. I stopped here and will know more once I test fire it. A lot of trial and fitting since I'm working with Cratex points and honing stones but experience has taught me that it's easier to take more off than it is to put it back on. Like a friend says; "I loaned out my putting-on files a few years ago and never got them back".
Right now, the angled face of the extractor hits the corresponding angle of the rim relief so to get the rim to seat on the bolt face, I have to push the dummy down which cams the extractor hook out of the groove slightly. On extraction, the hook will drop into the rim groove so it may not matter when firing.

Will share when I have more to report.