My Project

[robertmcw]

While waiting for the springs, I have posted some photos (not mine) that my shells look like.

[robertmcw]

The ones that don't get pierced are puckered (That sounds bad, did it not? And I have not had a drink in a year and a half, either).

RM

[Der Alder]

Sometimes when a primer gets peirced, the center of that primer gets blown back into the firing pin channel. When this happens the subsequent fired rounds will be either shallow or cratered like some of the ones you have shown because it is the peice of primer making contact with the next primer rather than the firing pin. This would be my guess as to the variation.

Aside from FP lenth/protrusion another thing to concider is ammo. Have you tried other types? Military ammo generally will have harder primers than commerical ammo.

[robertmcw]

I have tried about 4 or 5 types of surplus ammo with the same results.

[robertmcw]

Installed the Wolf extra hammer spring and it pooped the primer.

Looks I have some whittleing.

They are having a gun show this weekend in Houston. I will try to find a copule brands of ammo. I am thinking to try some Lake City M80.

I found this site and they say a M60 calls for a • M60 ......................Min. .035...............Max. .043

My fire pin is not set at .050 now.

http://m14forum.com/reference/94563-fir ... sions.html

Any ideas?

Robert

[robertmcw]

OK, I just set the pin to .045. It is too late today, so we will we see in the morning.

RM

[robertmcw]

When we welded the nose piece, the bipod section was a little short. Today I shot it with the flash hider tight with the .045 pin and it pierced the primer. Jbaum says the flash hider needs to be tight, but PERHERPS that is for a gun that in spec?

I tried backing back about three threads on the flash hider from tight and it shot it and it worked fine. Three shots, NO pierced primers. I still have a little bump on the ridge of the center of one the primers and I am temped to shave just about another .003, but they say if ain’t broke don’t fix it.

Today is it, except cleaning it and oiling it. Next time I will try a few more rounds to see it is really, really fixed.

Robert

[robertmcw]

I just went to the hardware store and got two c-lips to keep the flash hider tight. They add to about two quarters to the length of the receiver and it is tight now.

RM

[robertmcw]

It still popped a primer. I am stuck. I will try other ammo. I have some old South Africa ammo and I will see it that works.

[robertmcw]

Whittled the firing pin to .035 and it failed and put the medium hammer spring and it still failed.

Unless I use other ammo with fix it, I am out of ideas.

RM

[marknct]

Just wanted to make sure. Are you checking protrusion with the rollers out and the BC compressed tight against the spring?
Also, if you fire it and let it chamber the next round. Eject that shell and see what the primer looks like. I wonder if it's "pre- striking" the primer on chambering and then the actual hammer strike has very little resistance.

[robertmcw]

Well, I have not able to work on my semi MG42 for a while. I have purchased a BRP bolt (Second Pattern Bolt (machined)) but with I have not able to find it as we moved and the movers have hid my stuff into a lot of boxes and all my stuff is mixed up. I need to organize my stuff and with the holidays looming, when I can find my stuff, I will try again and report back. I have too projects and too little space. I need a shop.

RM

[42rocker]

Glad to see an update. Good Luck with getting everything straight.

Later 42rocker

[crash520]

Its NOT protrusion, its not piercing primers, your making it worse by shortening it, what your getting is primer blow out due to the firing pin tip not staying in the primer to support the thinned metal during the high pressure phase, if its a hammer fired gun, increase the hammer spring weight, reduce the firing pin retraction spring weight, the pictures of the primers bleeding back tell everything. It can also be caused by hotter loaded military ammo.

[Blanksguy]

Hi crash520,
You may be on to part of the problem......but because "RM" (robertmcw) hasn't posted a clear thread of where he started (past and current issues) and what is going on in a detailed clear order......the SA42 that he built may have other issues.

*********************************************************************************************************************************************
robertmcw,
I recently got to review this thread when it was brought back up from old-threads ..... your posting an update after about 14-15 months of being away.

What I am seeing are a few issues that need to be addressed, some of which may be from older issues (seen reviewing some of your older threads and/or replies to threads......(?).

When I see the case-head from the exploded shell-case in the start of this thread.......I have to ask if this issue with your SA42 was corrected before moving on with the pierced primer/un-supported-primer issues (?). This case-explosion appears as an "un-locked" bolt-head or bolt-rollers un-locking early.......(IE: High-pressure still in the chamber as the bolt is unlocked from the barrel-extension). Condition of barrel-extension and bolt-rollers should have already been checked at this point prior to your first "range-outing" and a non-issue now.
The NRA did a short write-up on "slam-fires" and how to "profile" the firing-pin-tip years ago......I believe that it was in reference to SKS-rifles and commercial-ammo with soft/sensitive-primers.

Did you insure that the Trunnion/Cam-Pieces were serial-numbered as a set (?).....and is your SA42-receiver "straight" and correct length (?).

On the pierced-primers.......this could be effected by a couple of things.......and as crash520 stated, unsupported-primers (firing-pin too short) will cause this. Also, an improperly head-spaced bolt allowing for some primer "set-back".
With that said, how do you measure "Firing-Pin-Protrusion" on your SA42 (?).

Also, what were the results of your checking of the Head-Space in your SA42 with the .308 barrel-assembly and SA42-Bolt-Assembly that you are trying to work (?).

When we get into the more detailed parts, and/or items to be checked, we may need clear/close photos of that part/area to allow us to better help you. A picture is really worth more than a "thousand-words"......so have camera ready, or be ready to type a lot of information for us to be able to help you better.

Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[robertmcw]

Thank for the pointers and as all the stuff is into larger mis-mixed boxes, it will take a while to find the stuff. With that said, it did not ever fire slam the weapon. That would be illegal and if it were to start slamming the weapon, I would have cut it up back to it pre mill status pronto. End of that story. I do remember when I built it, I used a camming piece with both numbers matching. I have saving MG42 parts for over 10 years – way before the German stuff started dying up and I have a LOT parts , I have tried about 3 – 4 German bolt new style heads and have a few of the old style head bolts as well and I am hoping the BPR bolt with a good bolt head will fix the issues. If that fails, I plan to ship to a good semi MG42 builder to fix it. I will then park it and duracoat it and save it for a rainy day or so if it just look at it and drool on it, it will not rust.

RM

[pathfinder]

Check the firing pin hole in the bolt head. If it is not supporting the primer you could have piercings even with the correct protrusion. Gas erosion will tend to open/bevel the hole. Your project is looking great!

[crash520]

unless a firing pin on any gun (centrefire) is more than around 0.055" protrusion it cant 'pierce' a primer, it simply is just not long enough, I hear the term pierced primer used way too much in the complete wrong text, unless the firing pin protrusion is excessive I call BS on anyone claiming pierced primer. IT IS primer blow back or whatever you want to call it due to, insufficient support of the primer during the high presure phase of firing.

[Blanksguy]

robertmcw,
Other than my questions from my last posting in this thread.....a couple more questions and photo request(s).

Is it a complete BRP-Corp. SA42 Bolt-Assembly (?).......or parts of a bolt for you to install the other parts from your present SA42 Bolt-Assembly (?).
Next, please post a clear/close photo of the firing-pin-tip you are using along with the current "Bolt-Face".

....and is the "Head-Space" correct (?). Thank you.

Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[robertmcw]

Richard,
Thank you for the reply – again all of my stuff in boxes from the move. It seems the weather will work me for the next month as I live in the Houston area and it looks I will able to sort a lot my stuff with some metal shelves I have and hope to get a handle on my gun stuff then. As the question about the bolt, I bought one of these (new in the box and I have not used it even I bought it early last year):
BRP Second Pattern Semi Auto Bolt Assembly (WITHOUT HEAD)
http://www.brpguns.com/categories/Semi- ... olt-Parts/
I have 2 or 3 semi wedges.
I have a two or three MG3 bolts and about 5 or 6 MG42 bolts and the 5 or 6 M53 bolts too, so I hope I can find them and pick one that works.
I bought a new set head space gauge and too is in the box(s). The barrels are new in the box Steyr 308 barrels I bought from DS Arms when they were selling them for about $100 each. And the answer your question – yes, all of the bolts and the barrels were in spec.
RM