Mg42 does not cycle 8mm but cycles 7.62 (conversion)

[badsnakeii]

I know I'm new here. I've been following and reading this board for quite awhile through my build.

What I've got. Early production mg42. Was cut behind the caming section so it would fit in a relatives footlocker. The original rear receiver was lost or destroyed throughout time. I acquired it after his passing when I purchased most of his guns the kids did not want. His wife told me I could have this box of junk or she was going to throw it out....I almost died. I soon realized the rear section of the receiver was not in the box. I ended up sending it to wiselite for reconstruction of the receiver and ended up being one of the first if not the first to have one built with the milled Gen 2 receiver.

Issue- I believe the wiselite receiver was welded on long and possibly canted or not parallel to the caming section. Reason being the recuperator was almost .200 from making contact with the barrel extention and the bolt head would hit and bind on the left top/bottom right corners. Fixed that by lapping the corners of the bolt slightly and extending the recuperator plunger. Also found out then that the Gen 2 receiver had an extra inch added to the back allowing the use of the original spring.
-I'm using the new brp semi auto bolt set. I was trying to use their spring at first until I found out the receiver was longer...
I cannot get the gun to cycle 8mm but it will cycle My 7.62 conversion flawlessly.
The difference you know obviously is the barrel, bearing, booster/cone. -the bolt fits looser in the 7.62 barrel than the 8mm. Go on the 8mm, Field on the 7.62.
The gas space in the booster is allot smaller in the 7.62, also the 8mm booster has a huge hole almost 14mm.

Has this been an issue for anyone else before?
I've thought about trying my 8mm barrel with the 7.62 booster set. Anything wrong with that? The hole is big enough for the bullet to pass through but the gas might be too high...
Could I need different booster cone for my 8mm set?
Could I need a different bearing for the 8mm?

Thanks allot.

[42rocker]

Welcome to the site. I'm at work right now so can't do much in the help dept. I post more after I get home. But I'll bet before then several others will chime in with a few ideas.

Later 42rocker

[Der Alder]

Being that the gun is already running good in 7.62, thats is a good sign, at least the recoup is working and such.

Your 8mm booster at size 14mm may be too big, especially on a new tight gun. I would look for an 11-11.5mm which are common in M53 kits. I see RTG lists "MG42" booster cones for $35 http://www.robertrtg.com/store/pc/MG42- ... 8p2534.htm You could email him and see what sizes he has and see if he'll send you an 11mm cone. He's a pretty good vendor to deal with.

Also MG34.com (AA) has booster cones for $25http://mg34.com/product/mg-42m-53-booster-cone/ again you could ask for a smaller size like an 11mm if he's willing to hand pick one for you. You can also weld them and re-drill them, but 11mm is pretty common so I'd try to find one of those first before doing all that.

IMO the 7.62 booster (which I beleive are 10mm) with 8mm ammo may be over gassed. I would try to get it run with the largest booster possible.

So on your recoil spring are you using a full length original type spring or a cut down original?
RTG sells used springs for $6.00 http://www.robertrtg.com/store/pc/MG-RE ... 6p2611.htm and new springs for $11.00 http://www.robertrtg.com/store/pc/MG-RE ... 6p2610.htm

I recommend getting some of both new and used at that price for setting up and fine tuning. I'm not sure what length you need with that extended receiver. You can always experiment with some of those cheap used recoil springs, cutting them to varying lengths. With an original length receiver I've had good luck with a 13.5" spring as a starting point. Your's may require one a bit longer - all we can do is guess.

You want it long enough as not to coil bind and bottom out on the springs when the BC is fully retracted. You can confirm this with the gun unloaded, top cover open and watch as you pull the charging handle back to its stopping point. If you do cut your spring put the uncut coil into the B/C seat. I always like to give mine a spin (turn) to make sure it's seated.

Others here may add some advice as well.
Good luck.

[42rocker]

Was thinking about adding a few things after work, now. But seems that someone has already done a great job of it. Another great thing about this site is the search button.

Later 42rocker

[JBaum]

The Wiselite receiver is longer to enable the use of a full length, uncut recoil spring. Don't screw around cutting a spring, it's made to run with the standard length.

I'd say your entire problem is an oversized booster nozzle hole. Get an 11.5mm booster and see if it works. 11.5 mm is listed in the manual as being a suitable replacement. An 11mm booster is made for .308. I wouldn't recommend using the 11mm .308 nozzle for 8mm. You don't want a smaller hole than is needed to make the gun function, as it just beats the gun unnecessarily.

[badsnakeii]

I'll see if my ffl has a smaller booster cone I can try. He thinks he just might have one.
Thanks guys. Good to know I'm on the right track.

I'm pretty sure search is just like most other things I've found here where I need to have 10 posts or something to use it. I've done my best using Google to search.

Looking forward to being able to use the FS section.
Thanks again for the help.

[42rocker]

10 posts is not hard. Ask a few more questions.

Later 42rocker

[badsnakeii]

Lol I know. Just was surprised. No other board I've been on has been set up like that.

[JBaum]

It keeps spamming the message bases to a minimum. Once again, a few azzholes ruin it for everyone else.

[Blanksguy]

badsnakeii,
Reading through your posts in this thread.......I would like some additional information on the issues when firing live ammunition to better assist you in getting your SA42 to fire live 8x57mm ammunition.

Please let us know the additional information as listed below:
1: What Top-Cover and Feed-Tray are you using when you switch from 7.62x51mm/.308 to 8x57mm (?)........or are you only using the 7.62x51mm conversion set-up (?).

2: You say the SA42 fires 7.62x51mm well......but only has issues with firing 8x57mm live ammunition.......correct (?). What exactly does the gun do after you load the first cartridge into the chamber, and position the belt correctly......and pull the trigger (?). Please explain in detail when the cartridges/empty-case stop when the bolt comes to "rest" and everything has stopped moving. Photos could help a little more, but please be in detail with either.

3: I won't go into testing parts and/or assemblies as the gun works in 7.62x51mm........but please let us know if the 8x57mm cartridges are not firing and only having the primers lightly struck by the firing-pin.

Your SA42 sounds like a nice addition to your "collection". Years ago, IMA and another company were importing MG42 Parts-Kits with DEMILed receivers where everything was cut off behind/to the rear of the cam-piece/"Trunion"......and the new owner would get a complete barrel-jacket with sights, and cam-piece/"Trunion" already mounted. They made for a really nice/quick build into an SA42 once a DEMILed (or new) rear-section was located.

Regards, RichardS
US Army, Retired

[badsnakeii]

Tried the 11.5mm one from my dealer tonight. Still no go. I wonder if it could be the barrel bearing is worn out??? What is the fit supposed to be on that? I've noticed when I pop the barrel out the bearing always follows it out. This I would think would be an issue in battle if the bearing comes out how do you get the thing running again until it's cold enough to put it back in? I shot it with the top cover off also and I can see it short cycle. Is standard 8mm not powerful enough to cycle one of these?

[badsnakeii]

1 I've had issues with the 7.62 cover and feed tray binding and haven't had allot of time to get the tight spots located so I've been running the 8mm top cover and feed tray with the 7.62 barrel etc.
2 Correct. 8mm short cycles every time. I've tried the ultra hot yugo stuff too. I'm confused on properly positioning the belt?
-I slip my starter tab in under the cover and pull the bolt to the rear and pull the tab through till it stops and I release the bolt. It feeds a round in about 90% of the time. Then I pull the trigger, recoil is low to the point it feels like a .22 went off. This is with all ammo even a hand load to what I considered red zone hot. As it short cycles it try to eject but never does completely and wads up the old case and bends the head on the next. It doesn't even reset the hammer. I've had it blow out the primers on the yugo and the turkish crap ammo a few times. Making me think it's an obd. But those typically go really bad. It dents the crap out of all primers. No light strikes, have had a few slow burners of the turk stuff.

So it could be an ima kit then?

[42rocker]

Something else to check out is Johns German books. One of them has a guide which you can make that double checks the bullet ramp feed guide on the top cover. Which if you have been having """7.62 cover and feed tray binding""" it would be one of the first areas that I would check.

Later 42rocker

http://germanmanuals.com/

[JBaum]

The barrel bearing should NOT fall out. It is supposed to be held in place by the same lever that keeps the flash hider from unscrewing. Check the tabs and the slots they ride in, make sure it moves freely. Does it pass the pogo test ok?

This gun should have gone back to the factory considering the problems it has already had, but I know saying that now doesn't fix it.

[badsnakeii]

Sorry not sure what the pogo test is. The barrel floats easy but the bearing isn't retained when the barrel is removed.

[42rocker]

pogo test -- take everything off the front of the front of the shroud and then press the end of the barrel down on the "floor" and after it is depressed allow the weapon to "rise bounce" back up. It should return to it's normal position. This is a test of the recup springs to see if they are working. You are pressing the weapon down so the barrel goes back into the shroud then releasing quickly so it will hopefully return (extend) to it's normal position. Like a pogo stick. If the barrel sticks or is slow returning then you need to check out the recup. Clean or replace the springs.
Also you almost have 10 posts. Did not know that salt6 (site owner) had the search button usage set to 10 posts.

Later 42rocker

[badsnakeii]

Ok. Did the Google search thing and kind of know what you mean by pogo. Pretty much what I figured you were meaning. I haven't done the test as a test...so I can't be sure and there is nothing with specifics I found as the proper way to pogo test. I've done it when I accidentally dropped my bolt in while forgetting to put the charging handle in first. It worked and unlocked the bolt.
Now to properly pogo (the proper way to pogo should be a sticky). Is I'd done with the bolt in and the recoil spring in also? Or are you just testing the recup to see if it'd good and has enough pressure to lift the gun on its own?

In my search for pogo I found there was a guy that had an MG he was trying to convert to an mg3 and was having the same issue in a sense that I'm having. He had to make his own booster with an extremely tight nozzle hole and had a short bearing?
The bearing in my gun for 8mm is the only non matching numbered part I can find. It has quite a bit of wear/erosion on the inside and on the face. I can compare to the 7.62 bearing and give a measurement and a difference between the two. Is there specs on what the length of the 8mm bearing should be? I'm guessing this kind of stuff is in the book mentioned above...

my 7.62 cover and feed tray are binding on closing. As to say their making contact in places on my receiver and need to be clearanced. The mechanism works 100%....so long as I don't have the same issue the other guy had with the feed pawls binding on the rounds as they pass under.

[42rocker]

"""Or are you just testing the recup to see if it'd good and has enough pressure to lift the gun on its own?""" that's the idea. Sticky, Slow or works well up and smooth.

Later 42rocker

[JBaum]

Sounds like Wiselite is still building disasters.

[badsnakeii]

Still curious if the pogo is done with the bolt and recoil spring installed?

Well they did better than some of the guns coming from century so I can at least be thankful for that. The did however rub me wrong when I got their bolt and grip for my build and they told me the bolt was the same design as the one sold by brp. Bahaha...right. they sent me a faulty grip and the bolt was a modified FA bolt body. The head it came with was a real German wamp marked bolt head so I kept that after agreeing to $40 for the head assy. Then I get billed for all the little pieces too for a grand total of $96. They Welched on the $40 price of course when I contested it. Pissed i was.