Light Strike – Eureka!

I think I’ve got it!

Or rather I should say that I think Don Plante figured it out.

I think he found the source of the light strike problem that’s been dogging my wad gun for a great many months.

And I will add a special thanks also to Kirk who comments here occasionally. He reminded me to save, not shoot, the light strikes so I could analyze them. It was having one of those failed rounds on hand for Don to inspect that triggered what I think is the solution.

But I’m getting ahead of myself.

Let me walk you down the path.

Here’s one of the light strikes. Notice the dent in the primer is not very deep. Apparently it wasn’t whacked hard enough to set off the primer so instead of going “Bang!”, it just went “Thunk.”

On any given day, these have been happening about 3 to 5 shots out of a hundred. For general plinking and shooting at empty cans and whatnot, that’s no big deal. Just cock the hammer and try again.

But for Bullseye shooters, a 5% failure rate means that in 60 shots of Timed and Rapid, you’ll have an average of three (3) shots that won’t go “Bang!” That means you are pretty much guaranteed to shoot at least one alibi string. And if another of those three clunkers show up in the alibi string itself and you’re not quick enough to re-cock the hammer, aim and fire, then you’ll be down as much as ten points. And if that clunker in the alibi string is not on the last round – there’s an 80% chance this will be the case – then there will be more rounds left in the five shot magazine that you don’t shoot.

At ten points each, that’s expensive on the score card. Real expensive.

Last Saturday after shooting the morning’s Leg Match. I told Don of my woes. He looked at the lightly struck round that happened that morning and we talked about different things that might be wrong. Many of them were things I’d already checked.

  • Bad magazine? Nope, the light strikes happen on all four of the magazines I tested.
  • Weak mainspring? Nope. It was replaced less than 200 rounds ago with a 19 pound fresh one.
  • Dirty firing pin tunnel, a burr in the tunnel or in the hole in the firing pin stop? Nope. All cleaned and carefully probed. No burrs. No dirt.
  • Bad batch of primers? Nope, the light strikes are happening evenly across three batches bought from three different places at three different times.
  • Short brass? Nope. The failures don’t have any preference for shorter than minimum, medium or even over-length brass.

At one point, Don took the firing pin out of my Springfield Armory Mil-Spec that, over the years and through several gunsmiths, has become my wadder. There are only a few “factory original” parts left in that gun but the firing pin is one of them. It’s what Springfield Armory put in there.

“This doesn’t look right,” he said. “Let me get a new one from the truck.”

As those who’ve competed at Phoenix Rod and Gun Club know, Don brings the better part of a gun store to the range. He’s got just about everything you might need, firing pins included.

The new (correct for 45 ACP 1911) firing pin certainly looks different. In this photograph, the new one is on the right.

The original firing pin came with the gun from Springfield Armory and I’ve been shooting with it since 2005. It could well be that it is within tolerance for standard 1911s because, in all that time that I’ve been shooting with it, while I’ve had light strikes before, I’ve traced them back, when I’ve bothered, to improperly seated primers.

Or at least that’s what I assumed “all the time” once I had actually seen a couple of high primers in the ammo I had made.

It was only recently that I started watching my reloading process more closely to avoid high primers, and added the extra step of double-checking after reloading and re-seating any suspect rounds.

With the ammo I’m shooting now, I am quite sure there are no high primers.

But the light strikes persist so I started looking for other causes.

With the new firing pin in place, Don donated five rounds so we could do a function check.

The five rounds fired, each on the first “Whack!”

But five rounds is not much of a test when the failure rate is a mere 5%. A hundred rounds would be better. But I didn’t have another hundred rounds with me so we did the next best thing; we looked at the dimple created by the new firing pin as opposed to the old one.

Here, look for yourself.

In this next picture, three shells successfully fired on the first strike are on the left. They all fired OK but they were hit (successfully) by the old firing pin.

Three shells fired with the new firing pin, again all successfully went “Bang!” on the first strike, are on the right.

Can you see the difference in the dents made by the old versus the new firing pin?

It’s not much and I had to photograph these from several different angles to find one that made the difference apparent but, yes, there is a definite difference.

The dents made by the new firing pin are consistently deeper. It is hitting the primer harder.

Returning home, I took the two firing pins and started doing some measurements with the calipers.

The new firing pin was 0.008" longer.

Would that make that much of a difference in dent-power?

Then, I weighed the two firing pins.

The old firing pin weighs 30.3 grains whereas the new one weighs 59.7 grains.


The new firing pin weighs almost twice as much as the old!

Remember your High School physics?

E = 1/2 M x V^2

Energy equals 1/2 the mass times velocity-squared. If you double the mass, you double the energy. If we assume that the hammer of the 1911 is massive enough to accelerate either firing pin to full speed – that hammer hits really hard so I think this is a safe assumption – then the heavier firing pin is going to hit the primer harder.

Twice as hard, in this case.

Look back at the picture of the fired shells. The new firing pin is making much bigger dents in the backside of the primer. The higher mass of the new firing pin is making the difference. (Don and I both shoot Winchester Large Pistol primers in our 45 ACP ammunition. All the primers in that picture are WLPs.)

I’m very excited by this discovery.

All the other differences I had previously found were in the “barely out of tolerance” territory. This was the first big difference and, with a doubling of the firing pin’s weight (and mass), that difference is obviously better at whacking the backside of the primers.

But it’s also true that the old firing pin was working 95% of the time, and it’s true that the shells where it worked on the first strike do have bigger dents than the one light strike seen in these pictures.

Most of the time, the old firing pin worked. Only occasionally did it fail.

Why? Why does it only fail some of the time?

For that, I can only guess.

Maybe the old firing pin because of its physical design and lighter weight was occasionally banging around in the firing pin tunnel and using up some of its energy – but only occasionally?

Or maybe a flake of carbon was occasionally plugging the firing pin hole or cushioning the primer where the firing pin would strike?

Or maybe I still do occasionally end up with a high-primer, or an under-length shell or a round with some other parameter slightly out of tolerance that, by itself wouldn’t have been a problem? But when meekly tapped by that lightweight firing pin instead of the twice-as-forceful whack of the new one, it didn’t go “Bang!”?

Small errors, left to themselves, can often be ignored if they’re within tolerance. But when several happen at the same time, they may cancel each other out, or they may become additive.

When multiple tolerances are exceeded and they are additive, things don’t work.

In aviation, that’s when airplanes crash. One error is survivable but when several happen, one on top of another in an additive way, really bad things happen.

Why the old firing pin failed only some of the time will probably remain a mystery.

But it was undeniably different, and it was definitely the wrong part.

The right part is in there now.

I won’t feel confident of a complete solution to my Bullseye light strike problem until I’ve pushed another hundred rounds down range. And I’ll probably reserve final judgement until that number is up around 200-300 because there have been stretches where everything worked just fine for several competitions.

But that wimpy firing pin was wrong. Someone at Springfield Armory stuck it in there because, most of the time, it will work.

Most of the time.

But now I understand what was happening.

(I’m a software engineer during the work week and I love discovering and fixing software bugs. It’s my passion. It’s one of the things I do very well. And when I get to do that elsewhere in my life, I find it every bit as gratifying.)

So, I’m excited. This is a clear difference that explains everything I’ve been seeing.

Another bug bites the dust?

Hope so. (I’ve got my fingers crossed!)

10/09/2012 Update: Fired 120 rounds in practice today. Every one of them went “Bang!” on the first strike. Problem fixed. Hooray!

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