Gun no work

[mp40guy]

Hi I have been building my MG42SA now for 2 years now and am having the following problems. I can shoot the 7.62 LC blanks no problem but when I change over to 8mm it dimples the primer but doesn't set the round off. I then take the rounds and put them in my K98 and they fire no problem. I have used steel cased Romanian and Egyptian rounds. It has an AR15 fire control with a wolf extra power spring in it. I have also changed barrels, trunions and firing pins.

[JBaum]

The MG42 doesn't have a trunnion, it does have a cam piece. The reason it's called a cam piece is because the cams inside it push the rollers inward when the barrel and bolt recoil.

When you change calibers, you trade the .308 parts (feed tray, top cover, barrel) for 8mm parts, right?

Take the barrel and bolt out of the gun and put the bolt head in the barrel extension. Do the rollers go fully out in the grooves of the extension? Does the firing pin go forward as far as necessary when the rollers are fully out? How is the headspace? If the headspace is too tight, the bolt won't fully lock.

Does the top of the hammer hit on the bolt extension (which slows it down, causing insufficient force to detonate the primer)? Can the hammer go far enough forward to hit the firing pin as far forward as necessary, or does it hit somewhere? Does the recuperator push the barrel fully forward so that the bolt rollers aren't held inward by the cams in the cam piece?

[hakentt]

Hi I have been building my MG42SA now for 2 years now

And I've built my MG42SA from parts kit in one day with basic tig welder and basic tools, I don't have a mill, I used dremel tool.

[JBaum]

And I've built my MG42SA from parts kit in one day with basic tig welder and basic tools, I don't have a mill, I used dremel tool.

Wow, that's really helpful to the guy. He should be able to fix it now, huh?

[42rocker]

jbaum
just remember there are some folks that you want next to you on the range and others you don't due to their quicker than everyone building habits.....

Ok, help for mp40guy, listen to jbaum, then think about buying any of the books that he might offer as they are good books about the mg42... Of course they are books that jbaum translate from "German" books, well they invented the weapon.....

Good Luck finding the problem...

Later 42rocker

[mp40guy]

OK I pulled the bolt out and barrel and all three barrels marry up nicely. I then checked the impact of the hammer and it is nice and square on the firing pin. The head of the pin is most of the way out of the bolt face. The next thing I intend on doing is looking for an 8mm headspace gage.

I think though I might need to get an FAL fire control. They are more powerful.

I will try to get a picture of the dimple that was on an unfired 8mm shell.

[mp40guy]

Here is an round that came out the gun unfired

[JBaum]

Barrel and bolt might fit nicely together, but the rollers need to go fully outward, not just part way.

Take the firing pin out of the bolt, put a cartridge in the bolt face, and put it on a barrel to see how it fits. The face of the bolt should be almost touching the barrel (or touching).

[hakentt]

Is that turkish ammo? That ammo is only for bolt action rifles.

[mp40guy]

No it is not Turk. The early Turk ammo was bad and they had to get help from Germany to fix it. Any ammo after 1943 is pretty good. This ammo is Egyptian made in the 1960's.

If I find that the head space is bad what do I do then?

[waffendude]

i think that is some of that mean- nasty- NAZI ammo---oh it should be banned--evil nazi stuff

mp40guy----one of the most common problems with the sa42 is the strength of the hammer spring---i think you are right abut the fal fcg--more power---with that said some of the surplus ammo has very hard primers---to hard for some of the semi's---you want to try some romy ammo --its seems to have softer primers.before i went to .308 i had the same problem with all the surplus ammo EXCEPT THE ROMY.

jbaum is the man for the 42---like someone posted above ---get a few of his manuals --they will help you understand the basic function---and as always is info is current and correct.
just my .02
waffen

[mp40guy]

So you have completely gone 7.62 and have no problems? I don't care if the weapon is 8mm I use 7.62 blank all of the time and the parts are cheeper.
I tried the 8mm Romanian steel cased and they didn't work

[42rocker]

Someone else might want to add more to this statement..

Boy that LOOKS like a great primer hit. I think that with a nice looking primer hit like that it should have fired.
From your posts it seems like you have had quite a few not fire. STILL looks like a good primer strike. Which should? mean that everything is locking up ok. Bad Ammo???? Blanks work live does not???? If blanks are working then it should be locking up ok. Good Luck listen to jbaum...

Later 42rocker

[Blanksguy]

mp40guy,
We'll make it easy on ya' ........

Light primer-hits in an SA42 can only equal:
1: Bad Head-Space....(Bolt-Head....Barrel-Assm./Chamber......or both-???)
2: Bad-primer/Ammo.
3: Hard-Primers where you need a stronger hammer-spring or heavier-hammer.
4: Out-of-Spec. ammunition seating too deaply in chamber (this is a head-space-issue "but" only due to the ammunition's "shoulder" being closer to the case-head so cartridge seats too deap in chamber.).

Now if this same bolt-assembly fired your LC-Blanks/US Ammo great.......I would look at the other listed items.
Also, your bolt may be good for that 7.62x51mm/.308 barrel.....but not with your 8x57mm barrel-assembly. Bolts/barrels are usually set-up/checked for a given "set" (Barrel-Assembly and Bolt-Assembly)....then numbered so they are not switched with another gun. Our guns being basically set up using random parts (no.....they are not matching Parts-Kits).....you may have to switch an assembly.
Check the items that you are using with a Go/No-Go Gauge set.......and you can check your ammunition with what it called a "Cartridge-Case-Gauge"....which is basically a SAAMI-Spec. "chamber" that you measure your cases and/or loaded ammunition in during "re-loading".

Regards, RichardS in MI.
Blanksguy2001@chartermi.net
PS: jbaum's books are a really good source of trouble-shooting information. Should pick some up.

[drooling idiot]

pic to blurry to be 100% sure but looks like a solid hit.
switch to .308 for testing, the available ammo is better than the 50 yr old 8mm.
your firing pin is it two piece? using the original FP up front? maybe replace that part. I've seen a lot that were heavily rounded.

[mp40guy]

I think I found the problem. I took apart the fire control and the pin that holds the hammer is broken in two. That might be the reason for the light strikes. The bad news is that the other parts in the fire control are so badly worn that they need to be replaced. I have only run about 500 rds through the weapon. It is a early Wiselite grip stick set up for an AR15 trigger pack. I got the parts for the trigger pack from Rock River Arms.