www.MG42.us

So I went out again today with the semi mg42. It would not fire at all the first 5 times I tried, I then placed a blank in the belt and it fired that no problem, then after which it started firing the romanian, sometimes up to 5 or 6 rounds before it would fail to set off the primer.

I fired over 300 rounds to do of which is shot off 180 of them. I looked at the romanian ammo. The rounds that were fired had very deep primer hits. The ones that were not were barely a tap on them with a very small indent. I reran some of the failed rounds and they fired fine sometimes with deep primer hits.

Likewise it did this with the 4 plastic .308 blanks I tried.. Sometimes it would fire them, other times it would not leave an indent at all.

So I am fully convinced it is not the ammo as I used different batches of romy 8mm this time and of course the blanks. Before it would not fire a round at all, and now it seems to be getting slowly better but at best I get off 5 rounds before it fails to hit the primer deep enough.

I am afraid if I get the new hammer spring installed, it will pierce some of the primers because looking at the ones it did cook off.. they are pretty deep. Any deeper would be a pierced primer.

Any idea's on whats up with this?

My other issue, is I can no longer pull the charge handle back to open the bolt as the latch on the receiver side holds it in place unless I manually assist it by pushing it off the ridge/latch with my finger and then pull back. It was not doing this before.


Sorry to make another thread but I want to make sure this gets read. I had a top builder build this and he basically said it ran great for him but it could be a head space issue with barrel or I should switch ammo.. neither of which I am willing to do because I have nothing but romy 8mm, im broke and I dont want to spend $100+ on a new barrel to "find out".

Thanks for reading.

Romy 8mm is great ammo to use. Keep it and work on the other items. Some pics of the charging handle please and pics of as much as you want to post.

Later 42rocker

Check headspace. If headspace is tight, the rollers won't go fully out and the firing pin can't go fully forward.

If it's good, then the firing pin could be sticking in the bolt and not moving freely. Try oiling it.

ncreptile,
There are several things that you can do, if you have not changed anything after receiving it from your builder (?).........some of which you may want to consider.
Question (?).....You statements about Romy-ammo and plastic .308 Blanks..............what barrels/assemblies are you trying to use/set-up (?).......and are all headspaces correct (?).

1: Go back to the "beginning".......your "builder" said it fire all of that ammo that he used without issue (?).......I don't know who you used, but get some of that same ammo that he used to check your SA42 (...... but I bet that he currently does not have that ammo on hand-?).

2: You have narrowed it down to just a few items to "recheck" as we know that you have already check everything....correct (?).
Again....starting from thre beginning (which is why the first-thread may have assisted you instead of re-writing everything that you did in detail. We need this in detail so we can assist you in any area that you may/may-not have checked or overlooked.
A light primer hits (knowing the ammo is not the issue) could be several items which are (but not limited to):
A: Condition of firing-pin......bent or too short or to tight in bolt-assembly (?).
B: Incorrect headspace.......and/or dirty-chamber.
C: Barrel-stop not being far enough forward during build and/or loose.......or issues of the Flash-Hider/Booster-Cup/"Nozzle" holding the barrel back slightly against the recouperator-assembly.
D: Piece of brass and/or dirt inside the SA42 Bolt-Assembly keeping the firing-pin from always being able to do its job......or possibly a bent or incorrect forward firing-pin-spring (used in some SA42 to keep system from "slam-firing").
E: Weak recouperator-assembly........this would show up as some of the un-fired rounds being slightly bent at the neck area of the case......try rolling them by hand on a flat table and observe the point of the cartridges. (IE: The barrel not being completely forward as the bolt chambers the next round for firing......this harsh-angle may slightly bend the tips and not allow full chambering.

.................well I've hit my max amount I can type with this part of my thread.......let us know what you find out.
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

OK.. More headache but at least the problems are allowing me an education on the subject.

The bolt would not come out.. at all. No sliding free, not even with light tapping of a hammer. I checked 2 different manuals including the BRP manual. I watched several youtube videos(including DARIVS even though his is FA).. Nothing would remove this sucker. I tried every way possible, even called "BRP" and he said "thats weird that shouldnt be happening you can remove the trigger group and it should slide out then".

SO I did that and it was surprisingly easy, along with that being easy the bolt came right out and I noticed some slight cuts to the trigger group metal on the side from where I tapped the hammer on bolt face to "force" the sucker out.

Nothing bent or scarred on the bolt it seems. The bolt is extremely dirty and I am going to take it apart tonight, clean everything out and then lube it up again.

I am debating on installing the hammer spring, but I am starting to think that is not the problem now that the rifle is firing 2 in 3 rounds. I did notice yesterday at the range, the more I shot it, the better it performed. I am HOPING that this heavy grease he used in there caught some gunk in it which was messing with the firing pin spring or the pin itself..

I do not think it could be a headspace issue since it was working fine for him? He was using czech 8mm(something I cannot find and if I could I'm sure would be to much for me at the moment)


@Blanksguy and others with list suggestions. Going to clean the bolt out fully tonight, I will then take it to the range and see if that does the trick. If not then I will get a headspace gauge and check for that and keep going down the list.
I really hope its just gunked up in the bolt as it is very filthy and thick and light grease/gel is everywhere on it.


Im learning
Thanks for the great advice so far.

FYI, you don't need a headspace gauge to check headspace. And because different ammo can be sized different, proper headspace with Czech ammo has no correlation to proper headspace with Romanian. Thick grease? There shouldn't be thick grease anywhere in the gun.

Have you done the "pogo test" to check the recoup?

If the builder has the gun full of heavy grease I'd degrease it and try a light oil and run it wet. Take some compressed air and blow out the firing pin channel when degreasing too, could be a chip in there.

Another area to look at is make sure the buffer was drilled deep enough for the firing pin clearance when recoiling. If its bottoming out there it could either bend the FP or peen the rear of it.

I'd check the head space or try another barrel, even borrow a barrel if need be just to rule that out.

Another thing, if you have a spare firing pin return spring, try cutting a coil or two off it. I'd do this with a spare though so you can go back to the other if thats not the problem. BTW, do you have any of the BRP firing pin spacers in it? If so try it with them out.

Try the heavy hammer spring if all else fails as well.

When you say the bolt would not come out when taking it out, is it maybe hanging up on the hammer? On mine, when I slide the bolt in, I have to reach in and depress the hammer with my finger to get the bolt to slide past it if the grip stick in place.

Besides the .308 blanks, have you tried any 7.62 NATO (.308)? Do you have the parts for the conversion you could try? I've seen a few of these semi guns sometimes choke on 8mm, but with the .308 barrel, booster and top cover run fine...something to ponder.

The fun continues.. I now cannot get the barrel back in due to the recouperator blocking it from being fully seated, its not even close to seating. I have tried removing everything at the muzzle, even removed the bolt and everything from the gun.

Tried using a punch and a hammer to drive it back but it is so stiff it just sends the punch flying forwards.

Any words of advice? Please tell me I don't have to take the recoup off and fix that?

ncreptile wrote:The fun continues.. I now cannot get the barrel back in due to the recouperator blocking it from being fully seated, its not even close to seating. I have tried removing everything at the muzzle, even removed the bolt and everything from the gun.

Tried using a punch and a hammer to drive it back but it is so stiff it just sends the punch flying forwards.

Any words of advice? Please tell me I don't have to take the recoup off and fix that?

The front recouperator retaining bolt has an angled surface. If that bolt is 180 degrees out and the angled surface is facing the wrong way, the recouperator piston with protrude about 1/4" out to far, making inserting the barrel almost impossible. Look at a cut away of that section of the gun and you will see what I am describing. If that is the problem, you will indeed have to remove the unit to fix it. Good luck. JH

Sounds like it's time to study the pics on this site of the recoup and look long and hard at yours. The easy question is that it still has the nut on the outside right? For the recoup to move that mush there should be a reason. Or if everything is in place, think to look twice. Again the "builder" said that he fired 200 rounds and it worked fine before he shipped it back to you?
A few pics might help out a lot in this case.

Later 42rocker

If it was me I'd send it back to the builder with a few belts of romy and tell him it has not worked since day one. If it was a home build that would be one thing, but if you paid good money to have someone professionally build it it should work. It can not be all Czech ammo (tested) vs Romy for all these issues. Tell him to record a vid of it running a couple of belts before sending it back.

That said, make sure the recoup retaining bolt is oriented correctly when you put it back together. See this recoup thread: viewtopic.php?f=39&t=1612 Maybe when he took it apart to finish it he got the bolt back in wrong?

The builder offered to take a look at it if I sent it back. But I frankly waited 14 months and I do not have a spare dollar after paying him $2400 to rebuild the thing to spend $100 to send it back to him and I sure as heck am not willing to wait 1-2 month minimum to get it back.

I don't know at this point. I lack mechanical skills to fix this thing, I cant sell it because legally its a home build(and I'd be screwed on price since it does not function well). I cant talk about the builder because hes #1 and well respected in this business and I'd no doubt have my ass handed to me by him and the community for questioning him.
I just felt for $2400 I'd get a working gun.. This feels like a boat I have poured my money into and have not gotten a single day on the water with problems persisting.

I am completely burnt out on this and do not know what to do. This is my dream gun(well next on the list) but I feel cornered with all roads either leading to me being more broke or the gun collecting dust in my closet.

Wish I had never wasted the cash


Problems to date
[*]Gun will not reliably strike all the primers, it will fire 2-6 rounds then fail to hit primer hard.(Builder says it already has the heaviest hammer spring in it so thats not the issue)
[*]The bolt will not come out of the gun unless I remove the trigger pack.
[*]Removed the barrel after I removed the bolt/trigger pack and reinstalled them. Now the barrel is being blocked by the recouperator and the trigger pack wont fire at all(however the bolt slides back and forth with the carrier fine.)

I know some of it is operator error.. I believe I did not reinstall everything right(though I was sure I did at the time)
However the bolt should slide out without me having to remove the trigger pack. Even BRP(who made the bolt and trigger pack) was baffled by this when I called.

Burnt out on this.. It's like if I even get it put back together I am just going to be rewarded with a $20 range fee and a non functional weapon.

After my pitty party post I went and once again completely disassembled the gun.
Still the bolt will not go out or in without the trigger pack being removed. Once I got it all back together(minus the barrel of course), the trigger would not release the hammer, almost as if it were jammed into something blocking it.

I took it apart again, the trigger worked fine when not in the gun.

I tried putting it back together in all different ways.. No luck.

Emailed the builder and asked his opinion, it may be best just to send it back to him with the 8mm Romy(separate boxes of course) as Der Alder suggested as the problems seem to be mounting.

Gun will not reliably strike primer's of any 8mm used.
I have to flip the bolt carrier/charge handle catch by hand in order to move it.
Barrel will not go back in.
Trigger not working/bolt refuses to go in unless trigger pack is off.

I will see what he says and man up, send it back to him if he suggests. Frustrating.

The one good thing about all this is I feel I have a very good grasp on what everything on the gun is for and how it all works. I also feel safe taking it apart and putting it back together.

If at all possible can you post any pics so we might be able to see a few areas and offer better suggestions? Also if you paid $2,400 to this person to weld it up I'm hoping that he was a class 7 FFL and did put a serial number on it for you. That said from one of your post it seems not. There are a lot of folks on this site that can help you out. Lets see a few pics.

Later 42rocker

Lets take this one step at a time and start from the beginning. It's sort of tedious, but we have to start confirming or ruling out things step by step.

Perhaps you can take it apart again (field strip) and start one piece at a time, noting each problem and taking pics.

Being you are having trouble geting your barrel in, lets start at the front and work our way back. With the FH off be sure the barrel bushing is installed correctly, it should slide freely inside the bearing.

Try inserting the barrel, keep the FH and booster off at this point...are you still having trouble with the recoup being too far forward to get the barrel back in? If so snap a pic of recoup's front through the barrel door so we can see where its at. Also try flipping the barrel, try it each way. I know it sounds silly but I've seen some barrel extentions fit tighter one way than the other.

If its ok, close the door/barrel, a hard slap from the heel of your hand should be all that’s needed to close/lock it and seat the barrel.

While we are at it, lets take a measurement now (being there are so many unknowns at this point).

Assuming the barrel is fully extended now to the barrel stop with the recoup pushing fully forward. Measure from the end of the bearing face (top of the threaded part) to the top of the bushing...what's your measurement? Should be 13mm.

If all goes well lets do the pogo test next. Set the gun standing up on the floor with barrel end down. If you push the gun down it should spring back up like a pogo stick.

With that out of the way we will move back next.

Pretty sure its not the front as it moves freely up there. I redid the front twice just to be sure.

Builder again offered to take it back and see whats going on so I will take him up on the offer and report back with the findings ASAP. He is being very helpful about it so I cant ask for more at this time.

I'd grab some pictures and video of it but I already have her boxed up.