My Project

[robertmcw]

Here is a photo of my MG42. It was a 3 cut from Dan (Angola Amory). The welder got in a hurry and the last piece got warped. I called IMA when they were selling the cut pieces and I got a set with the same date code (FG) and the same dfb code and the numbers were really close from the two parts, so, we did a little operation. When with the RTG repair kit was selling the Germans were using the straight the receiver, it is really close. Then I bent the receiver straight with a sledge hammer and except about two small dents (and that will fix with a tig) and that is all I am going to do with the receiver, except I plan to install a dust cover with pins at the front of the grip stick.

I used the blocker just like the fourth down photo here:
viewtopic.php?f=10&t=11774

It still has issues piercing primers but I THINK the fire pin is too long. I using jbaum’s gauge, the fire pin just fits over the larger slot.
With my Harbor Freight caliber, the gauge it reads MAX .070 and MIN .055.
I have reading here this that “Postwar, this was further reduced. I have a Rheinmetall G3 manual that specifies firing pin protrusion at 1.45mm( -0.31mm), (max. .057", min. .045").” (viewtopic.php?f=39&t=8862&p=67748&hilit ... ors#p67748)
It seems most gun guys think the fire pin should be in the .040 - .050 area for a 308 NATO round. Any ideas? I really don’t mess up with the pressures of a 308 round.
I have tried with a new German bolt head and a new barrel and the headspace specs are right.
I have a FAL bolt and the fire pin is shorter than the FAL fire pin and it is shorter than the MAX gauge and it has never popped a primer yet, so does mean my fire pin is too long?
I have bought one of jbaum’s books but I really need to get the MG3 one and I will as soon as the next check clears.

Then after it all done and I am happy with it, I will park it and Duracoat it and put it in the safe and save for ammo.

Robert

[42rocker]

Robert
Looks really good. Sweet even. Set up on .308 from the looks of it. Getting another firing pin to help check the amount the firing pin comes out might help to review as to filing back the firing pin or replacing the bolt head. Good Luck on that stuff you are down to the final tuning up.

Later 42rocker

[robertmcw]

Thanks, I have working on it for over 8 years. A little here, a little then, and then it got where were now. Yes, it is set up with 308. I wanted to have the option to use both links and belts.

Robert

[robertmcw]

I shot last week and mounted it on my tripod and it hit a 8" stump at 100 yards a couple times. Not bad from scrap?

Robert

[robertmcw]

This the tool I used straighten it:

http://www.robertrtg.com/mgreceivertool.html

I fought to use some blocks when hitting it so that is why the dents. It works well.

[robertmcw]

The problem with pierced primers is that the when the gun is shot, the pressures travels back from the firing pin through the bolt hole. Then the heat and the gunk from burning the gun power turns into abrasive material and it will make the hole bigger and bigger and it can create safety issues. I have always had issues with having pierced primers with my made from scrap home-brew MG42/MG3 SEMI. I tried up to match a firing pin to match an FAL 308 firing pin so see if that I can fix that.

I used my RTG SEMI MG42 fire pin and my handy Harbor Freight caliber to measure the top of the firing pin from the bolt face and jbaum’s bolt gauge. I measured the pin with the MAX gauge and it was too long and it was popping primers. I decided how long the fire pin I was going to design. I made the pin shorter – just under to the MAX length and it was still popping primers. I used a cordless drill with a knife type stone with oil on it, but it was not cutting it (hahaha). Then I chucked in an electric drill just for a fraction of a second with my bench grinder and then I measured it again and it is close where I wanted – more close to the MIN gauge. Then I used the electric drill using a stone with oil again and rounded the fire pin into a more round shape. Then I measured the pin with jbaum’s gauge with the MG3 bolt. The round of the point just touched the MIN gauge. I looked that the FAL bolt I have and it too is just touching the MIN gauge.

I shot the MG42 SEMI and had NO PIERCED PRIMERS.

I have been shooting most of my life and I know what a spent shell look like. Most of the primers had pierced primers before I fixed this fire pin. They had ones that had intact primers had cratered the primer like an impact at the moon, except the ones that had pierced the primers. The shells that that not pierced the primer had a crater that was deep and they were rough at the hole walls and high. Today, the primers set at the MIN gauge looked better and the impact with the fire pin was not as deep and still they were touching tops of the walls of the where the hole goes. Then I had to stop. I have my own land but I still have neighbors and I don’t want to bother them too much. I will try again next week while they at work and try to re shaping the fire pin more of a dome shape to match the FAL pin. I HOPE that if all 25 are OK, I think we can say that certainty that some of my issues with piercing primers with a 308 round using a MG3 bolt can solved with a shorter fire pin. If not, it is back to the drawing board. If it works, that is it end of this post.

Look, the fire pins that RTG has one length of pins and are pins are for all types of bolts. Now BPR mow sells a new type firing gin with special washers to adjust the length. It makes since to custom the firing pin to fit YOUR bolt and barrel. The problem is you get too heavy handed, or if you too much of a hurry, you will mess up the part. Ask how I know. This time I did it slowly.

So we are on the same page, this process is for my made from scrap home-brew MG42/MG3 SEMI (that will not fit a full auto bolt OR a full auto grip stick) with a AR-15 trigger and disconnector and hammer set up with a newer MG3 style bolt and a new in the box Strer 308 barrel. I have no clue what the right way is to work on a full auto MG42/MG3/M53 is. If you adjust your firing pin, you adjust it at your peril, and if you mess up your fire pin or your gun then talk to the hand.

[robertmcw]

OK, I shot it today once and I have good news and more good news. First off, the welds held (good news). I set up with my tripod and when I shot it, I heard a more of a sound more than I am used to and there was a lot of smoke. (That was not a good sign and this is why you really need a tripod before all of the bugs are solved.) I opened the top and I was looking at a stub of a cartage hanging off on the bolt. The door was bent. The receiver was not fazed or budged at all. I used my trusty rubber hammer and fixed the door and it looks good as new. I then pried the rest of the shell and the primer was NOT DAMAGED (the best news). The firing pin was not bent or damaged at all (more good news). I was using a RTG semi main spring, so I think I will go back to using a German spring with 4 coils cut off. I think the shell was not seated right and the rollers did not engage all the way and I had an OOB. Then I had to fish out the remaindering of the brass. Then I need to have a chat with the hand. Now, with the pressures being less than in the chamber, we still need to if the firing pin will pierce a primer but that is all of the fun for today.

[42rocker]

Glad to hear you were not hurt. Well been there done that. Used the rubber hammer and fixed the door. In my case it was the firing pin sticking in the back to the nylon ring due to hammer strikes flaring out the back edge of the firing pin. Also in my case the brass came apart and I still have a piece stuck in the chamber. Going to get that out some day, I hope. So check the inside of your barrel chamber.
Had to laugh (a little sorry) when I read your statement about doing the initial shooting off a tripod. I had shot a lot of rounds off my lafette. First time I'm going to shoot off a bipod holding everything is when mine happened. First time off a lafette, special part, I had also just asked my daughter (over 21), first time to feed the belt when it happened. Might not be able to talk her into feeding the belt again. Everyone was fine in my case also. Thank God.
Make sure the firing pin moves real easy.

Other than a bent door your MG42 looks real nice.

Also fyi Brian @ brp is the one that normally makes most of the parts that are sold out there. Brian worked hard on getting a lot of those parts in production.

Later 42rocker

[robertmcw]

42rocker

"due to hammer strikes flaring out the back edge of the firing pin" We countersunk the buffer. It is hardened and it is tough. I had snapped one fire pin before where the buffer hit the pin before I fixed it.

I checked the chamber and it seem to be OK. Thanks for the heads up.

There a LOT of pressure in a 308 round (Maximum pressure 62,000.0 psi (427.475 MPa).

[42rocker]

Brian (brp) and I talked about what happened and we talked about the fcg hammer hitting the back of the firing pin. Well I use the brp main spring (rtg sells them) but I will also check the buffer area after your words.
I would say that the main thing is,, that it sounds like everybody was fine afterwards.

Later 42rocker

[robertmcw]

I was looking at the striker sleeve and the fire pin goes all the way to the face of the bolt, whether or not the striker sleeve is engaged with the rollers in the bolt. Perhaps the firing pin itself could be re-designed so the pin itself CAN NOT fire out of battery? With the fire pin that BPB has, there are two bumps the length of the pin. What if he used THREE bumps so the extra bump would COULD NOT hit the shell (the primer) UNTIL the sleeve is engaged with the rollers? The extra bump (between the face of the fire pin and the spring stop) could small enough to keep the sleeve from moving to the right depth of the pin (not like it goes all the way through the sleeve now) yet still keep the spring big enough to move the forward spring stop from keeping from moving after the bolt assy. has just locked the rollers?

I had a lot of coffee this morning, so I may talking out my hat.

RM

[robertmcw]

I would happy to pay him to do it and ship the bolt and the barrel to BPR for a custom fit. He could sell me 3 or 4 extra pins at the same time.

RM

[robertmcw]

Here are the evidence today. I will make the pin just a little shorter.

[robertmcw]

Fixed the door. It is still just out of whack but I will really fix it when I am done.

The German spring has much more zip.

[Der Alder]

Another thing you could try is maybe a longer or stronger firing pin spring. That may solve the problem of peirced primers and OOB's and the same time.

[robertmcw]

I got one of the medium hammer spring from BRP and got yesterday. The hammer has a weird shape. I just found a new in the box regular AR-15 hammer in my magical box. I just installed both parts and we can see if that helps. Thanks for the tip. I will try it in the morning and report back.

RM

[robertmcw]

The BRP hammer spring will work but the hammer sits to high and a AR15 hammer won't fit in the grip sick and that is why the hammer looks like that.

[robertmcw]

I have an old panaceabeachbum grip stick and it uses the AR-15 hammer and it has not changed or cut or filed to change the shape of the stock hammer. The problem is the trigger slap is pretty bad. Even with normal hammer it failed the primers.
I tried to shorten the pin today all but one of the primers were pierced. I thought to use my “Bubba” lathe and chucked it in the fire pin to high and used the stone so it have about a 60 degree slope on the pin and removed that slope about 1/8 of the side of the point to decrease the size of the diameter on the point and then I tore some strips from a sheet of emery paper I had and polished the side of the pin and the point with more a point than a dome shape I had doing. The drill is in the vice and the pin ready to "lathe".

I started with the pin and did not write the findings down. I then thought keep a log.

Looking for (max. .057", min. .045") firing pin protrusion for MG3 Bolt in 308 round.

Protrusion
.054 Pierced
.053 Pierced
.051 Pierced
.050 2 of 3 pierced

I found a 308 with a new primer that has not reloaded (no power or no bullet). The primer looked GREAT.

I plan to keeping it shorter until either it works and it fails because it too short to pop the primer.

I have to take a break for this for a couple days and it may rain, so I will keep you posted.

Robert

[42rocker]

Sounds like you have a plan. I believe that I also have the same gripstick. Not sure because I bought it off another member here. But it works good for me.

Good Luck with the firing pin project.

Later 42rocker

[robertmcw]

I just ordered a couple extra hammer springs from Wolf. I want to try that before I whittle the pin more.

RM