still popping primers

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Jason

still popping primers

Post by Jason »

been working on the fp profile and still I get the dimple where the firing pin hits the primer. I took the fp down so far that it would not hit enough to fire so now my minimum protrusion is .024. the fp is as blunt as I can get it while still beening somewhat rounded. should I make it so less area of the fp tip hits the primer?

maybe the headspace is the problem. I do not have go/no go gauges (yes I know I should) but just from measuring the brass the headspace seems fine. measuring from the datum, line the fired brass measures the same as what my m1a chamber is spaced to and there are no other signs other than about every 5th or 6th primer is poped.

Is I possible that the fp hits the primer too hard?

other than when the primer pops it will not eject, everything else seems to work fine.


I am fresh out of ideas on what to do other than try a diff bolt/barrel. :?
ak47dennis

Post by ak47dennis »

Jason, is this with 7.62 X 51? Because mine will also do this with some types 7.62, not to concerned cause if load the 7.62 Austrian blank, South African or Hertenberger the problem goes away. It has NEVER done this with any 8mm regardless of the type.
slowfinger

Post by slowfinger »

Dennis, Is there a reason why the 8mm wouldn't be punctured ? Because my Bren gun has been poping PMP ammo lately. So I talked to LEN S. and he sent a shorter 20. pin to me, wich I hope cure's it's ills. Will see shortly. BTW. hope you care to elaborate on Jasons problem. Slowfinger :)
Jason

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Post by Jason »

the ammo is aussie .308. the only other ammo I have is reloads and factory. the winchester blows every primer.
huntsinmtns

Post by huntsinmtns »

Jason,

what are you using for your hammer spring, The Wolf spring is very high spring pressure great for 8mm but overkill for 308 I believe, try the stock hammer spring and see what happens.
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Post by Blanksguy »

Jason,
Again.......what is the diameter of your Firing-Pin?....and the diameter of the firing-pin-hole in your "Bolt-Face? (IE: Is this a "worn-part" issue? ...where soft-primers are "flowing" iinto this area when fired).

Thanks, RichardS.
Jason

'

Post by Jason »

I really dont have a way to measure the fp hole, but the fp seems to fit very well with almost no side to side movement.

the hammer spring is a regular ar spring, although I did bend the lower spring arms a bit to get a little more umph. maybe I should bend them back?

for some reason I never tried my reloads until I saw what ak47dennis posted. I just tried a few rounds and the primers looked much much better, although I had to cringe every time the trigger was pulled (fully preped good stuff for the m1a) the load is 1 grain under max with cci 200 primers. does this mean I have to reload? If so the brass cant last for more than a load or two with all the pushing and pulling. never had a head seperation and do not want to start now :shock:

what I really need is a sample pack of millitary ammo for expreimentation.
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Post by Bullwinkle »

sounding more and more like OAL/Headspace...you might try a few different BARRELS and or bolt heads if you swap them out....308 headspace guauges are fairly inexpensive. You will probably find a mil.surp ammo that will run great due to minor OAL/heaspace differences. South African, Portugeuse or Radway Green might just be the ticket...
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Post by Bullwinkle »

Just re-read your post....WINCHESTER Blows everytime...if your shooting .308 commercial and it is blowing then it's almost certainly headspace/pressure as the .308 max cup is noticably higher than 7.62. You could be right on the very edge of dangerous headspace and the added pressure of .308 vs. 7.62NATO is telling you something. Headspace guages will be cheap insurance in this case.

reaming the chamber a few 1000's or finding a worn /eroded barrel to shoot should help...have anyone close you could swap with??? Dan with Angola Armory has Steyr barrels in OKAY condition that would have enough wear to simulate an deeper chambered round/headspace...
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Post by JBaum »

There's an easy way to test headspace with an MG42 without guages.

First, make sure the chamber is SPOTLESS. I suggest a big bore brush and an electric drill on the end of the cleaning rod to make sure the chamber is perfectly clean. Dirty chamber = tight headspace. When the dirt falls out, the headspace testing goes with it.

Since you use a live roud for the test, take the firing pin out of the bolt FIRST, and take out the anti-bounce spring, which if you don't have, you should get (full auto only). Remove the barrel from the gun. Put the cartridge in the bolt face, and insert the bolt into the barrel extension and see if the rollers travel fully out to the outside. If they don't, the headspace is too tight. If they do, then it's not too tight and should function just fine. I know guys who run the MG42 in full auto with no problems at all with barrel/bolt combinations that can close completely on the no-go guage. It doesn't seem very sensitive at all to excessive headspace (within reason), but tight headspace is a major problem. Remember, if the bolt rollers don't go the whole way out, then the firing pin can't go the whole way forward, but if it's just right, it's possible to blow the base off a cartridge because the bolt isn't fully locked up, but the firing pin comes forward enough to make it go bang.

If the headspace is too tight, try a different combination of bolts and barrels. I have 3 bolts and 7 barrels, and there's one, and only one combination that headspaces too tight. I wrote it in the barrel carriers which combination not to use.

I just used a caliper on a couple bolts, and my firing pins stick out 68 thousandths. I don't have problems running mine, so I would use that as a basis for what's about right.

As far as rounding off the front point goes, chuck it up in a drill and hold sandpaper to the point. Round is correct, not rounded with a taper.
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Jason

'

Post by Jason »

thanks for the replys.

when I check the headspace with the live round, the wedge that pushes the rollers out bottoms out on the back of the bolt head then you have to pull the rollers out the last +/- .065 with your fingers. they move completly out when you pull on them, does this mean the wedge is worn and is not holding the rollers all the way out causing it to not lock up completly? Or is it normal to have a little play at the end of the rollers travel?

the wedge has a slight flat area near the nose where the rollers would sit when the gun is 'in battery' although even with the play in the rollers, I cannot pull the bolt head away from the bbl face more than a couple of thousands of an inch. the flat area almost looks as if it has been peened down from the rollers beating on it when they unlock from firing

when hunts did the bolt work he told me the bolt was extremly worn.

the more I type the more I think this wedge peice looks fishey.



jbaum's headspace trick should be saved for everyone to read and check as more of these guns get built :D
Jason

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Post by Jason »

btw the .065 of roller movement is a wild a## guess. I just held it up to the calipers and moved them back and fouth. nothing scientific about it.
Karbinator

Post by Karbinator »

Jason,
Do you mean the pin is Puncturing (?) the primer.....

I can't figure out this conversation, as to why a "dimple" on a primer is
a problem....... I'm certain it's something I've yet learned, but I thought
all guns 'dimple' the primer to some extent.

Only waky thing I've ever had happen with primers was the other day on
my 1919, and after 180rds the barrel was smoking. The bolt put a round in the chamber
and It shot the round...then smoke came out from under the top cover. I found the
round jammed in the barrel, and the brass corners ripped square from the bolt slots.
The Primer was BLOWN off the brass.....gone....see right through it. I've never seen
such a thing happen, but It's my first belt fed.

In reading this post, I wondered if your winchester was Blowing the primers off
like what I mentioned, or something else.
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Post by salt6 »

Pictures of the primer and cartridge would probably help the discussion.


Steve
ak47dennis

Post by ak47dennis »

Scroll 1/2 way down... BRP seems to be having the same problem!!!

http://www.brpguns.com/mg42semiowner.htm
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Post by TOM R »

good find dennis :D , there is alot of useful info there :idea: maybe we should see about permission to copy some or all for the faq section
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Jason

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Post by Jason »

Dennis you da man :D

in there statement about "modify the stricker to engage the rollers more firmly upon lock up" is exactly what I was trying to ask about in my long winded post above.

I was waiting to get a reply or two before the dremel went to work on the front of the stricker (wedge) so it would push the rollers out a bit more. I'm going to give this a try and see what happens. guess the worse thing would be having to order a new bolt.

Karbinator, if you follow ak47dennis's link you will see a pic of the hole in the primer like some of mine are. they explain it so much better than I can. I guess in my next semester of WECSOG I'll have to take creative writing :wink:
Last edited by Jason on Tue May 10, 2005 11:10 pm, edited 1 time in total.
ak47dennis

Post by ak47dennis »

Jason

Is your locking piece/wedge WWII or post war? Because if I am not mistaken the post wedge does begin to drive the rollers out sooner. I am using a post war MG3 wedge, couldn’t bring my self to drill thru a part with a beautiful waffenampt.

If I had my digital camera handy I could post some pictures to highlight the differences.
huntsinmtns

Post by huntsinmtns »

Here are 5 strikers if you notice 2 are not the same all have different dimensions although they the difference is about .003-.009 between them, this is a average. The larger on the 2 on right is WW2 the others appear to be post war but not sure as some have no markings. I will put on optical comparator and measure angles and post results here for you guys. Looks like I'll be posting for awhile instead of machining so if certain pics needed can do.
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Post by Intruder196 »

ak47dennis wrote:Scroll 1/2 way down... BRP seems to be having the same problem!!!

http://www.brpguns.com/mg42semiowner.htm
This article convinced me to stick with 8mm :)
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