Shotguns: Pierced Primers, Firing Pins, and such.

["Big Boston"]

My recent project was loading some 16 gauge 2 9/16" ammo for my turn of the century 1897 Winchester shotgun. The hull I was working with was a pre-primed Cheddite, and as such came primed with Cheddite primers. My load data did call for Cheddite primers so all was golden. However, visual inspection of my first test firings showed up some pierced primers. Cheddite primers are a bit thinner in the cup than some other 209 primers, but changing to a different primer would be the same as turning up the radio when the engine in your car starts making noise. To every issue there has to be a root cause, that's just the way life is, 

 

My first order of business was to examine the firing pin. The super heated, high velocity of the escaping gases can very quickly erode the tip of a firing pin, gas cutting IOW. Once damaged, the frequency of primer piercing will increase, making the situation worse, until the firing pin will need replacing. 

 

First a few pictures:

 

    

 

The purpose of the pictures is so I can better describe  the entire situation, the what happens. I knocked apart a few fired 209 primers from my spent primer tray, it's entirely possible that none the primers in the picture weren't fired in my '97. They are for the purpose of illustration. 

 

It's been my experience that most shotguns have a pretty stout hammer/striker spring. As you can see, the firing pin drives fairly deeply into the primer cup. In fact, it drives the primer cup into the anvil of the primer with enough force that the anvil dents the cup. The anvil, being a bunch pointier than the firing pin actually pierces the cup. Even if the cup can withstand this blow, if the firing pin is long enough and the hammer spring strong enough, the anvil will eventually dint the firing pin. Once dented, the firing pin will eventually start piercing primers, or allow the anvil to pierce the primer, because the firing pin surface will not be smooth anymore. the cup will not be able to stretch evenly over curvature of the primer, it will fracture or tear.

 

My first order of business was to check the tension on the hammer in my '97. In a Winchester '97, the hammer spring tension is adjustable. Not an easy adjustment, as the action needs to be disassembled. The hammer adjustment screw was tightened down snug, so I loosened it. This issue dealt with, it was time to examine the firing pin, more disassembly. The firing pin wasn't very smooth anymore, and it was a bit too pointed IMHO. So, I tuned up the tip of the firing pin as well. 100 years and use will tend to damage a firing pin, instead of being nice and round, they become pointier, and start to resemble the tip of a center punch. 

 

I did a bit of searching, and discovered the desired shape of the tip of a firing pin isn't exactly standardized or talked about much on forums. 

 

 

The firing pin that you see on the top of the picture is a picture picked off the interweb, a used firing pin. The tip is no longer smooth and it is starting to get a bit pointed. For illustration, or dramatic effect, the diagram below the firing pin is of a chisel, whose 60° pint is meant to drive through metal, not the shape you'd want for a firing pin. 

 

I'm no gunsmith, I've owned a few shotguns, and I have "tuned" up the tip on more than one shotguns firing pin.

 

The quickest fix is to file the firing pin flat on the tip. The lowest diagram illustrates this. This does 2 things, it shortens the firing a bit, but minimally, and it creates a shape that has less of a tendency to drive into the cup. Much like the meplat on a SWC pistol bullet limits penetration in ballistic gel. I first saw this firing pin shape on an expensive Italian shotgun years ago, IIRC. This shape tends to minimize thinning the primer cup area that strikes the anvil. As the cup and anvil contact, there is less force pulling metal away from the contact point. anyways, that's how I see it. 

 

Sometimes the amount of damage dictates the best shape. The pointiest I'd go to would be a dome, like the right edge of the red dot below the chisel. Again, IMO, a better shape would be the curve of the white line. 

 

Some 209 primers have thicker or "stronger" cups and resist piercing better than others, but all primers have the basic same design for the anvil. I don't know why they have to be so pointy and sharp. Back before I was a pup, some shotgun primers were assembled with a large pistol primers, and the anvil in a pistol primer is rather dull when compared to a shotgun primer. In addition most shotgun firing pins are long(ish), and I suppose this is to compensate for the less than precise shotgun ammo out these. 

 

BB 

 

  

 

 

 

 

[Garrison Joe, SASS #60708]

Well, you aren't going to change the primer anvil shape from how they've been made for a long time now.  So you are left with changing primers or fixing your gun.

 

Cheddite 209 primers are RENOWNED for being very thin and easily pierced.   They are DEATH on the bottom-barrel firing pin of a Browning Citori O/U shotgun, which striks the primer a sideways blow rather than perfectly straight on.   Yep, I've had to replace pins in my sporting clays Citori after 1000 rounds, and in a friend's Citori after a few more thousand rounds.   Once the pin tip is ragged enough to tear the first primer, it's not much longer before the hot gases erode those firing pins to the point where the bottom barrel won't fire reliably.  Then, you need a replacement at $50 or more.

 

I would believe that swapping to other primers is NOT like "turning up the radio to hide an engine noise."   In shotgun shells, in some guns, the Cheddites are the real root cause of the problem, and swapping to a better made primer, like a Win 209, really does stop the problem.  A pierced primer in a Win 97 really suggests the firing pin may be a few thousandths too long.   The most common shape I've seen for shotgun FP tips is a hemisphere.   Flattening the tip may work for you.  I would not do that until I had tried other primers.  The firing pin is also easily shortened at the "hammer" end on old shotgun designs, and then you are neither changing the shape of the tip nor removing any surface hardened layer of metal.

 

Good luck, your mileage and firing pins may vary, but Cheddites are still pretty "thin skinned" to work with.

GJ

 

["Big Boston"]

Thanks, after some more measuring, I too believe they are too thin. About 0.005" thinner than a W209. That's significant. However when I measure Fed 209's, the primer cup is about the same thickness (or thinness) as a Cheddite. Winchester primers are thicker. So it would seem that although thin, a Cheddite primer should not normally pierce. However, a strike by a firing pin at an angle will put the primer cup under more strain. 

 

Theoretically, IMHO, if the firing pin is not inline and completely parallel to the bore center line, at least the hemisphere on the tip should be. I had a Zoli 20 ga that pierced primers like a fiend, bottom barrel, and IIRC, the only primer the wouldn't was a Win 209. I also flattened the tip on the lower pin. 

 

 

I gleaned the following information from the "Great Google". Shotgun firing pins are in the neighbourhood of 0.125" (1/8 inch) in diameter. The more common shape of the tip is a true hemisphere. Therefore the tip extends by a distance equal to the radius of the body of the pin, past the full diameter, or 0.0625" (1/16 of an inch).  That is also the maximum that they should extend past the face of the breech. The minimum seems to be 0.050". On my 16 ga '97, it extends a bit more than that, around 0.070".

 

I don't like to mess with primer substitution in shotgun shells, so before I swap I'll contact the load data source. 

 

BB

[John Boy]

I reload 16ga Cheddites for a German SxS using Win 209’s. Ever reload goes off with no punchutered primers  

["Big Boston"]

 

I reload 16ga Cheddites for a German SxS using Win 209’s. Ever reload goes off with no punchutered primers  

 

When you loaded your Cheddite hulls with Cheddite primers, how many pierced primers did you get? Did you try Federals or CCI primers?

 

I'd also like to know what your firing pin protrusion was.

 

Cheddite primers are about 0.001" larger in dia than a Winchester 209, and on my hulls they fit snug enough, IMO. I was loading a different recipe, it called for a Win 209, but unfortunately that load had other issues. My load that calls for Cheddites is better in that regard.

 

I don't have any loyalty to Cheddite, or their primers, I'll ditch them in a heartbeat, when I get the go ahead from BPI.

 

BB

["Big Boston"]

I have an 1897 "C" that I've been resurrecting. The project is progressing and I've been doing a bit of test firing. 

 

When I was testing some Challenger Extra light loads I noticed quite a few pierced primers. I like the ammo, so I resolved myself to the fact that I would have to fix the shotgun, make it work with Cheddite primers. 

 

I backed down on the hammer spring, then I trimmed a bit off the firing pin tip, and reshaped it as well. I don't know why Winchester 1897 shotguns have firing pins that protrude so far. I researched the subject again, and for the most part 0.050 to 0.055" is the typical spec for most shotguns. Some sources list a minimum of 0.035". I've measured a few 1897's and they all protrude more than 0.050". At around 0.070" the pierced primers stop, so I stopped there as well. I polished the tip and gave it as round of a shape that I could do. 

 

I think that because it has to reliably fire when slam firing, Winchester left the firing pins a bit long. I also believe that primers from back in the day were a bit heavier built than todays 209 primers. 97's don't seem to experience light strikes or misfires.