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MG blew up in my face! Need help

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Re: MG blew up in my face! Need help

Postby JBaum » Fri Apr 14, 2017 10:56 pm

hakentt wrote:Can't find anything about headspace, bunch of worthless threads come up. Can you please do the same check I did and report here?


REPORT: I guess I did the check with the same amount of ambition you did. I can't find anything but a bunch of worthless threads either.
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Re: MG blew up in my face! Need help

Postby hakentt » Fri Apr 14, 2017 11:08 pm

jbaum wrote:If it's too much trouble for you to look for it when you're the one who wants the information, then it's too much trouble for me to find it for you. I don't care to read a bunch of stuff about headspace just to be able to find what YOU want, when you won't do it for yourself.

I did search, but understand that we are talking about 12 years of posts and you did post a lot. Many links and photos are not working either.
There is one post on headspace tutorial, and it is a total mess. It is a very simple measurement

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Re: MG blew up in my face! Need help

Postby Der Alder » Fri Apr 14, 2017 11:52 pm

its all there if you look...all I can say at this point is good luck..over and out.

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Re: MG blew up in my face! Need help

Postby JBaum » Sat Apr 15, 2017 12:23 am

hakentt wrote:It is a very simple measurement


Actually, it isn't.

There are two different ways to measure headspace, one for rimmed cartridges, one for rimless. The methods for measuring each are quite different, as they measure different dimensions of the chamber/bolt area.

You're shooting a rimless cartridge, and measuring headspace with the rimmed cartridge method. It doesn't work that way.
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Re: MG blew up in my face! Need help

Postby hakentt » Sat Apr 15, 2017 12:45 am

jbaum wrote:You're shooting a rimless cartridge, and measuring headspace with the rimmed cartridge method. It doesn't work that way.


Really? You are treating me as a noob but you forgot that I joined this forum only one year after you. So I have been around. I have successfully built and headspaced two Yugo M76 8mm rifles from parts kits. I understand the basic concept. I just wonder what is the secret behind MG42 head spacing, it is not even coming up in the google search engine.

Image

Based on all of my measurements even though I am not getting any help here, I determined that my 'Cartridge end play' and 'Forward bolt clearance' is within specification, meaning my headspace is within spec.

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Re: MG blew up in my face! Need help

Postby messerschmittfan » Sat Apr 15, 2017 4:55 pm

If you will go back to my original post and the second one I sent you I noted that there was nothing wrong with your head space the problem is that camber on the end of the barrel. From the photographs you attached you can see the ring at the base of the cartridges, as well as on the separation of the round that blew. That says that the cartridge is seating into chamber and that the bolt lugs are engaging before the firing pin strikes. The problem is that the end of the cartridge does not have any support than the head of the bolt. That will case the pop. For setting headspace on both my MG34's and MG42's I use the standard 7.92x57mm go/no-go gauges, if I remember correctly I purchased them off eBay a few years ago. I run at least 1,000 rods through my guns every year and never have had a case issue. Again I think your problem is NOT the headspace but the extra large camber on the end of your barrel. Just my thoughts but if you use that barrel with that large camber in it again be sure to have a first-aid kit handy. Harry

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Re: MG blew up in my face! Need help

Postby JBaum » Sat Apr 15, 2017 5:03 pm

jbaum wrote:messerschmittfan is absolutely correct. With that much of the chamber missing, I'm surprised the first three shots didn't blow too. Looks like that barrel is scrap. Where did you get it?


As I too have said before, messerschmittfan is absolutely correct. This problems is caused by the back of the chamber being drilled out and missing.
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Re: MG blew up in my face! Need help

Postby hakentt » Sat Apr 15, 2017 7:33 pm

jbaum wrote:As I too have said before, messerschmittfan is absolutely correct. This problems is caused by the back of the chamber being drilled out and missing.


I am not talking about MG3 barrel anymore, I am talking about my green mountain 8mm barrel that has identical chamber to my original Yugo, so that is not the issue.

For setting headspace on both my MG34's and MG42's I use the standard 7.92x57mm go/no-go gauges, if I remember correctly I purchased them off eBay a few years ago.


go no go gauges mean nothing on mg42 but you guys keep talking about it like it is a must. It actually can be bad on MG42 because perfect headspace on the gauge may be too tight for MG42. Go no go gauge is something you must use on bolt action rifles or on firearms that has the action hidden where you can't physically inspect the chamber, but in MG42 you take out the extractor and you can pretty much use live round, I got some aluminum tape that is 0.10mm thick, so I can use that to measure exactly how much slack I need to have but if I don't have good combination to compare to then I can ask you guys for help, but if you are not willing to help fellow MGer then all I can do is guess work.

Here an old thread where some guy had similar problems but worse than me. viewtopic.php?t=453

here is what Jbaum wrote then:

If the rollers won't lock up fully with the GO guage in the chamber, try a different combination of bolt and barrel. Check the length of the ammo, and compare it to the longest guage that the rollers will lock up with. This is done out of the gun, with the bolt and barrel sitting on a table. Make sure the locking rollers extend completely to the outside of the grooves. You can remove the firing pin and try it with a live round if you like. A little loose on headspace seems to make no difference. A little too tight and the rollers don't lock completely and the base of the cartridge blows off from lack of support. A LOT too tight, and the cartridge blows off the back, and can destroy the receiver.


Here is my green mountain barrel combo with 1973 Romanian round inside, with bolt fully locked I get '0' clearance between the round and bolt face, if I pull on the bolt I get 0.50mm slack and only slack is in the rollers vs. cam grooves. Can someone do the same test I did? I actually may have a bit tight headspace and may have slight out of full lock firing once things get hot.

greenmountbarrcomp1.jpg


Ok so I did another test with the spent shell that has the most pronounced ring and found out that the rollers do not fully lock with this shell. This indicates that my 8mm shells show out of the full lock firing. Now I really wonder it head space is too tight

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Re: MG blew up in my face! Need help

Postby JBaum » Sat Apr 15, 2017 9:05 pm

Reminds me of an old saying:

Technically it's possible to have a mule climb a ladder. But it ain't gonna happen.

I hereby officially give up. I've tried several times, and it just isn't working.
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Re: MG blew up in my face! Need help

Postby hakentt » Sat Apr 15, 2017 9:38 pm

jbaum wrote:I hereby officially give up. I've tried several times, and it just isn't working.


I asked for few measurements and you don't want to do it. My hands are tied

Can anybody give me this measurement of your Yugo barrel?

DSC01609.JPG

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Re: MG blew up in my face! Need help

Postby messerschmittfan » Sun Apr 16, 2017 2:46 pm

Funny that the German Wehrmacht and the modern day Bundeswehr issued a tool called a Werkzeugpatrone (which is a go/no go gauge) along with Stahlpatrone (chamber gauges) to their Waffenmeister for the MG42. So I find it hard to believe that you think that the go/no gauge has no use in an MG42. They were used much like you are doing in checking your barrel and bolt timing. The main difference being that they were using a standardized precision tool instead of a production round to set the timing. I assume that you are checking the free space between the round with the rollers locked. When I was training with the Bundeswehr I was told that the distance/thickness between the base of the cartridge and the bolt face was that of a piece of paper which provided the proper free play (timing) when the barrel and bolt where held up perpendicular to the horizon. The locking rollers were to be held in and the bolt to hang freely. This is for a FA weapon as the bolt and barrel are still moving forward although locked when the firing pin is striking the cartridge. For my semi-auto's I simply use the go/no go gauge as it is a precision tool and insure that the locking rollers are locked when the firing pin is struck. Works great for me with no problems like you are having. Have you tried steel cases?

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Re: MG blew up in my face! Need help

Postby hakentt » Sun Apr 16, 2017 7:12 pm

I am asking for measurements, if you can measure your good working Yugo barrel that will help me a lot. There is a reason why this forum is kind of dead, people get told to use search all the time then why even bother posting anything anymore, everything has been discussed.

When I was training with the Bundeswehr I was told that the distance/thickness between the base of the cartridge and the bolt face was that of a piece of paper which provided the proper free play (timing) when the barrel and bolt where held up perpendicular to the horizon.


piece of paper is 0.10mm(.004) thick.

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Re: MG blew up in my face! Need help

Postby Sw1ngK1ng » Fri Apr 21, 2017 11:50 pm

Technically you can headspace an mg with a live round but you best hope it is 100% to spec which is very unlikely and you still won't know if it too deep. I don't know if you have the gauges or not but if you don't, get them. Nobody that knows what they are doing will tell you how to headspace with a live round rather than the gauges because you will likely end up making a high stakes game of jack in the box. Fundamentally, headspacing an mg is the same as most other rifles, go gauge should go in easily and the bolt should close, with the no go gauge the bolt should not fully close. DONT let the bolt slam closed or you could possibly ruin your chamber.

If your headspacing is too deep then you will need access to a lath and have the patience to only remove small amounts of material at a time. The part of the barrel that may need facing is the part that the front of the barrel extension tightens against. If the chamber is too tight then you will need a chamber reamer to further cut the chamber. If you don't have a lath and the knowledge of how to accurately set a barrel in one I do not recommend doing the headspacing yourself.

Also, someone else's measurements on this part will not help you at all. These rifles do not simply have interchangeable bolts and barrels. You can buy several already headspace barrels with the extension already installed and your bolt may only have proper headspacing with a few while someone else's bolt could fit others that yours did not.

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Re: MG blew up in my face! Need help

Postby blackreichswehr » Sat Apr 22, 2017 10:49 am

hakentt, I am not attacking you on this-- you are closing your eyes to the advice and answers to your question, your looking for a simple measurement? it's like your asking how to wind a watch with a pair of pliers.

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solved

Postby hakentt » Tue May 02, 2017 4:54 pm

Update, cause was old over-pressured Yugo 50s ammunition. With new chrome line barrel it took more pressure to get the projectile trough so pressure was increased, this resulted in over-pressuring the brass case and case getting sticky in the seat when the seat got hot and would result in fail to eject. Ammo worked fine on my dark bore worn out Yugo barrel because it was easier for pressure to move the projectile down the bore.
I ended up buying full matching M53 kit with nice new looking matching barrel. Installed all the parts and had the same result. Then switched to Romanian steel case 1973 ammo and not a single problem.
To further prove my findings I gave the guy at the gun range link of 100 rounds of same Yugo ammo to try on his original never cut FA MG42 and it ran until round 40 and it stopped with fail to eject with previous 3 rounds showing signs of over-pressure. He also has good barrels.

blackreichswehr wrote:hakentt, I am not attacking you on this-- you are closing your eyes to the advice and answers to your question, your looking for a simple measurement? it's like your asking how to wind a watch with a pair of pliers.


I am not closing my eyes on advice. I understand the basic concept of headspacing and it turns out I was right and using my common sense I established headspacing was OK. Other people here have their eyes closed with their "you need that tool or forget it"

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Re: MG blew up in my face! Need help

Postby messerschmittfan » Tue May 02, 2017 5:19 pm

Reminder that I asked if you had tried using steel cased ammo as it seems to work better in all of my guns, both MG34's and MG42's. Harry

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Re: MG blew up in my face! Need help

Postby JBaum » Tue May 02, 2017 5:55 pm

Just someone else using junk ammo in an otherwise good gun and having problems.

Move along, there's nothing to see here. :lol: :lol: :lol:
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