Bizon Shooting update/Accident Report
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Thread: Bizon Shooting update/Accident Report

  1. #1
    Gunco Member jungp's Avatar
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    Default Bizon Shooting update/Accident Report

    Wanted to update y'all on what's been happening with my Bizon.

    First, the rear trunnion (stock tang) got loose from the frame. The recoil of bolt carrier smacking the rear trunnion was too hard. I had to weld the rear trunnion to the frame. I moved the trunnion half inch forward this time. I can use regular hammer and trigger instead of modified version.

    Second, I modified the magazine release to be like AR-15 instead of AK. You push the button on the right side to push out the latch on the left. Had to make a small slot on the left side of the magazine and magazine well.

    Third, I enlarged the ejection port.

    Fourth, The bottom of the bolt face was filed flush (looks like mauser bolt face instead of remington bolt face.


    Shooting Report:
    I shot three magazine on Saturday. Reliablity went up dramatically with these changes. However, I still have an ejection jam per magazine. The empty case is lodge between new round and the bolt carrier. I think the extractor is not engaging reliably. Any idea?

    I made above modification after my shooting accident two weeks ago. Not sure exactly what happened but here is what I think happened. When I charged the gun, for some reason, the bolt was not slamed all the way and the extractor was not engaged. When I pull the trigger, it did not fire since the bolt has to be forward all the way to have the hammer to hit the firing pin. I did not realize the extract was not engaged at this time. I pull the bolt back again (thinking the round that was in the chamber was dud) and let go. I heard a loud bang and I felt something hit me 1 inch from my left eye (at the very end of my left eye brow). I was bleeding. I believe the new round hit the primer of the round in the chamber. Not sure. It just happened so fast and I can't recollect exactly.

    Anyways, the wound healed up nicely. However the bump on my eye brow has not gone down and it felt rather hard. Yesterday I was trying to pick a way the scab and realized that the scab was not scab at all. It was a small metal piece protruding from my eye brow. I put a small refrigirator maganet on and it stuck.

    I asked my wife to perform the surgery but she just could'nt do it. I got an exacto knife and cut one eight inch from the bottom and one eight inch from the top and got the metal piece out. There wasn't much pain when cutting but it was nerve wrecking. It was a quarter inch sqaure piece of copper coated metal. Yep. It was schrapel of the Wolf 9mm!

    Lessons learned.
    I was not wearing a safety glasses at the time. I usually do when I go shooting. But not at this time. It could easily been my eye.

    Firearms can be dangerous. Use good judgement and assess risks (a trait most male species lack).



    At this point, I am not sure what I can do to enhance the reliability. I think AK-74 recoil spring may not be strong enough. I have seen unburned powder in the chamber area. I've been toying with the idea of adding a second recoil spring on the barrel (like CZ-52 7.62x45) attached to the modifed gas piston. I have AR-15 recoil spring that I tried but it doesn't seem to have enough power.

    Any idea would be appreciated. I am at the end of my patience with this project.

  2. #2
    Gunco Veteran Steelcore1964's Avatar
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    thake all that 9mm crap......... package it up and send it to me......
    That which does not kill you, makes you stronger

  3. #3
    Happy Camper hcpookie's Avatar
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    I think you had an out-of-battery discharge. Wolf 9mm ammo may have too light a primer for a free-float firing pin. You may want to consider a spring-loaded firing pin. Most commercial-grade primers are too light for free-float firing pins. Military-grade primers are a different story.

    You would have to use a threaded insert on the rear portion of the bolt to accomodate a spring-loaded firing pin.

    Frankly, I would ***ONLY*** use the tire-and-string method to fire this rifle until you fix it. That metal could have hit your eye, you could have had an OOB slam-fire situation, or a million other things. You should feel lucky you just have a small cut. Not trying to scare you, but no one's safety is worth experimenting with a cool project.

    The only thing I can say about the reliabilty of the rifle is that you should use un-modified parts, as the AK action is a known standard. You could use that as your basis that the "known" is functioning properly. I'd say that the OOB discharge you had should have you VERY WORRIED until you identify the reason why- if you don't know EXACTLY why it happened the first time, it could happen again.

    Was the rear trunion riveted? Those look like screws. Did you use red loctite on the screws? You may want to ensure that all screws are torqued down T-I-G-H-T. I have done only one screw build, just to say I have. I cut the holes under-sized so the screws are in there VERY tight. This gives me a bit more warm fuzzy about the screws. If you find a screw loose, degrease it with brake cleaner or the like, and zap it with some red loctite to be sure that sucker is in there solid.

    The extraction problem sounds like a classic stovepipe situation. While I agree with the spring idea, have you checked how it ejects with hand cycling? Remove the firing pin, load up a mag and charge it several times. Set a box or laundry basket on its side and drape a towel over it to catch the bullets (keeps you from walking all over the garage looking for that one round that likes to roll under the workbench - ask me how I know ) Then hand-cycle the mag. You should get solid, crisp extraction and the bullets should jump hard into the towel. Even on my Uzi the bullets will fly out there with a little bit 'o spice. Then check the cartridges - look for a wear pattern where the extractor claw touches the bullet. Also check the rear of the cartridge for a deep bite of the ejector. Here's a trick I learned from Winn - you can see the wear pattern very clearly if you color the outside of the bullet with a sharpie magic marker. The wear pattern will INSTANTLY show up! That should be enough for you to determine if the extraction is good or not.

    I wonder if it is getting a good connection to the rounds when stripping them from the mag? You stated you have a Bulgy '74 bolt and an Uzi barrel. You should be OK with extraction, assuming the extraction lug is un-modified. You may want to check the up/down location of the magazine when charged. Do you have another 9mm to compare it to? The bolt should hit the rounds very very very close to where the magazine's extraction channel is located.

    Safety First!

    hth,
    - Jerry

  4. #4
    Gunco Member jungp's Avatar
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    Thanks for the info Pookie. I will look into those. If I recall correctly the ones that did not eject were Wolf. I had mix of Wolf and Winchester white box. I hope someone would make 100% gun soon so I would know what I have done wrong.

  5. #5
    BANNED jpglee1's Avatar
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    First...use the AK-47 spring, not 74 (I believe it's stronger...) also, make sure you are not shortening the spring at all. Believe it or not, if you do it right there is room in there for a FULL length 47/74 spring and about 1/3 of another one behind it. On my build my receiver is 2" shorter and I still have room for all that spring I personally use the 47 spring preloaded about 2.5" using the recoil spring rod and a washer (the washer is what the spring sits on...I slid the washer forward while compressing spring then welded it until the spring was compressed, called preloading it) if you still have problems hit the hardware store and play with their springs. You can also do a HEAVY spring to backup the original spring...make it sorta progressive. Stick with the Mini-Uzi for a model, it has a similarly weighted bolt. Use it's spring rate as a guide....

    Sounds to me like your ejector is not in the correct spot. I had to move mine forward over 3/4" from the original AK spot. My bbl lines up roughly where the 762x39 BBL would have gone originally. As the 9x19 case is approx 1/2 as long as a x39 case you have to adjust the ejector accordingly. Sounds to me that your bolt is running off the magazine before it ejects the round, allowing the next round to pop up in front of the bolt before the old case is popped outta the receiver?? I also had to really open up the bolt carrier to get enough room to allow the cases to clear reliably... Hang in there boss, you'll get it!!!! I also designed my new recoil spring guide to have a bolt-stop built into it to prevent over-travel. This translates into a little more recoil bump on your shoulder but it keeps the bolt from popping out of the receiver slot and also keeps the carrier lined up w/the mag better....
    Good luck and thanks for the update!!!!

    BTW< Mine runs and works fine. It did before I took it apart to re-build the trunnion, so Im sure it will now also. I just have had lots going on in my life and have not had a chance to put the trunnion back into the receiver. It function tested OK with dummy rounds with trunnion C-Clamped in place and receiver bolted down. I would give the snout of the carrier a good wallop with a rubber mallet and the dummy round would eject across the room and the new dummy round would feed in...did this 15 times or so before I got bored. It used to shoot OK before but I was worried my old trunnion setup was too weak (never took pics of it...sorry )....

    Dont give up Jungp! It's just teething problems any new design goes thru. Good luck!!!

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    BANNED jpglee1's Avatar
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    Oh yah...forgot to add... ON MY bolt I had to thin-out the push-channel thing at the bottom of the bolt (the part that goes thru the magazine's channel and pushes the next round forward...) Originally it was just a tad tooo thick for STEN mags. I wanted to be able to use any sten mag I found, so I modded the bolt instead. Basically just used file and sanding disk on Makita grinder until it was acceptable. YOu might also want to look at shimming your magazine to see if that helps. Sten mags/mag wells are notorious for moving around. The sten mag will move 1/4" side to side in a std. sten magwell, thats another reason I chose to use the Mac-11 magwell, it supports the magazine over a 4+ inch area and you can squeeze it to get the magazine to stay lined up better... Just something to think about.... Sorry for dub post. Take care.

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    Gunco Member jungp's Avatar
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    Thanks for the info JPGlee1. I am using AK-47 spring from AMD-65. My receiver is 1.75 inches shorter than orginal so there is some preload. I will try to slip another spring to see if I can beef it up.

    Would you mind taking a picture of your ejector with the magazine inserted. I would appreciate the view from the top. Currently my new ejector sits slightly ahead of the magazine lips.

    Where did you open up the bolt carrier, under side?

    I did thin the bolt so it will fit the sten mag since the channel on the sten mag is round and little narrower than.

    My mag well does not have any play from side to side. I made the magwell and it is little tight with some magas.

    Currently, I am moving to my ranch. I have decided I had enough of the city of Dallas. So all my stuff is packed. But good news is that once I unpack and build my shed, I can build and shoot on the same spot.

  8. #8
    Gunco Member cwtoyota's Avatar
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    jungp, You may want to try the recoil spring from a German G3 rifle, or a Spanish CETME rifle. They are chambered in 7.62x51 Nato (.308 caliber) and have a much stronger spring. The recoil spring in the G3 looks like it is the same diameter or extremely close to the AK/AKM rifles. I'll take a measurement for you and compare the spring rates side by side this evening after work. If you don't see me post here with that info, ping me via e-mail or PM to remind me.


    I'm pretty sure that if you start stacking up or shimming the recoil springs you will experience coil bind before you make much change in the spring rate. I'm not saying "it won't work"... just that it may not work well.



    At this point, I am not sure what I can do to enhance the reliability. I think AK-74 recoil spring may not be strong enough. I have seen unburned powder in the chamber area. I've been toying with the idea of adding a second recoil spring on the barrel (like CZ-52 7.62x45) attached to the modifed gas piston. I have AR-15 recoil spring that I tried but it doesn't seem to have enough power.

    Any idea would be appreciated. I am at the end of my patience with this project.

  9. #9
    Gunco Member cwtoyota's Avatar
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    That brings up a very good point. Typically, a light bolt and heavy spring will cause higher cyclic speeds while a heavy bolt and light spring will cause slower cyclic speeds. There is a good balance for any firearm, however the slower cyclic speeds of the heavy spring and light bolt have shown to be more reliable and more controllable.

    What I'm getting at is that you may want to stick with the standard spring and add some extra mass to the bolt assembly.

    On my 9mm AR, I think it has a regular spring (not 100% sure, so don't quote me on that), but it use a much heavier buffer.

  10. #10
    Gunco Member jungp's Avatar
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    Thanks everyone for input. Per CWToyota's suggestion of heavy bolt and light spring, when I get the lathe unpacked in June, I will turn a 5 inch rod 5/8 in diameter and screw that into the bolt carrier and see what happens.

    I did try adding more spring but it did have spring binding issue.

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