Pierced primers

[dpl_hcm]

hello

my NO4MK1 is piercing primers with SB ammo only and only 2 or 3 out of a box.the ammo works fine in 2 other enfields.any ideas?i thought bolt head, but mine is at the high for number2 and seems to be flat.im thinking firing pin and spring?PPU runs just fine in it with no issues.any thoughts or ideas would be great help.can i use my bolt from my other enfield and just use the original head to test if its a firing spring or would that be a issue with headspace?

dennis

Information

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[Son]

You need to check your firing pin protrusion. If it's ok, then check the radius on the tip of the firing pin to make sure it doesn't have any tiny sharp spots. I don't know myself, but can anyone say if the primers in the SB ammo are softer than others?

[Bruce McAskill]

It's the S&B ammo that is your problem. Their primer pockets are cut on the shallow side forcing the primer to back out more when fired causing the piercied primers.

[dpl_hcm]

i could beleive the ammo being a issue but it works fine in my other enfield.maybe a combo of both ammo and pin.but main question could my bolt head be a issue or not?would the pin and spring be the difference causing it not to work in this enfield?bolt heads are hard to come by!


thanks

[Peter Laidler]

It can only be a couple of things. Sharp (or deformed as stated by Son) striker and/or soft primers and/or excess striker protrusion

[Bruce_in_Oz]

Add "enlarged or deformed" striker hole to the list.

Once you start rupturing primers, the problems accelerate. The super-hot jet of escaping gas acts like a cutting-torch and eats away at the striker and hole. This erosion causes further roughness of the striker tip and enlargement of the hole. Having a "perfect" striker tip and an oversized / out-of-round hole is also a recipe for rapid damage. This will often show up as little discs of metal being punched out of the primer cup by the annular jet of gas driving the work-hardened material rearwards. This, in turn causes more deformation of the primer cup, leading to even more gas leakage and cutting. Some WW2 production Arisakas are classic examples of this.

The deal is that the striker must have the correct form, smoothness and protrusion and the hole must be round and closely fit the the striker. It didn't matter too much back in the days of black powder. However, the pressures and temperatures at which smokeless propellants operate require much closer tolerances. One of the major feature of ALL military rifles that were developed in the late 19th Century it the amount of effort that went into diverting gas from ruptured primers way from the firers face. Note the vent holes in the Lee-Enfield bolt heads and the exhaust slots in a Mauser bolt. There was obviously a bit of an "issue" with such events, and the designers took it seriously.

An additional note is the ring formed at the diameter of the primer. If you are getting gas-cutting there, you may have excessive headspace. When the primer ignites, it tries to back out of the pocket. On a tightly headspaced, rimmed cartridge, this effect is small; on rimless cases it is quite noticeable. The only thing stopping the rimless case from moving forward is the relatively soft shoulder. This is why one should NEVER re-use cases used for very light loads as the basis for full-house loadings.

When the propellant charge ignites, the case is usually slammed back and forces the primer back flush with the head of the case.If you are using commercial ammo that has little or nor crimp on the primer, this action is quite fierce.This is one of the reasons military ammo generally has an annular retaining crimp on the primer pocket.

[Peter Laidler]

I see the point(!) so to speak Bruce but on that basis, surely you'll be getting ruptured primers BEFORE you start to wash or erode away the striker hole in the bolt. In other words, the ruptured strikers are causing erosion of the striker hole........... No!

[dpl_hcm]

i called SB ammo and they were great on the phone a 10+ they are going to look at the ammo just to confirm no issue.so im sending back 1 box with the piercings in it.i did notice the ones with the piercings the primer seemed to be pulled out as so to say the pin grabbed it.i took a real close look at my pin and there is a hair edge that my nail can barely grab.im leaning toward this pin so i ordered 1 and once i get it in ill see.

dennis

[Peter Laidler]

Don't forget dpl that replacing a striker isn't just a case of screwing the old one out and screwing a new one in. The bolt is set up around the striker and bolt head. If I was you, I'd re-radius the striker tip ensuring that the protrusion remains at between .o40" and .050". Just ask if you need further technical advice

[Parashooter]

Maybe this will help -



All it take is a few minutes with some fine-grit abrasive paper or stone. Usually the pin can be nicely radiused and polished without reducing its length more than about .002". A magnifying glass helps.

As the lads are saying here, the most common cause of pierced primers is the firing pin - it's very seldom the ammunition or anything to do with headspace. When full pressure builds in the chamber, the primer cup has to stretch a bit to conform to the pin and surrounding bolt face. If the pin is rough, the cup tears instead of stretching nicely. Imagine poking a toy balloon with your elbow and then with your fingernail - same principle!