Thursday, March 20, 2014

So What Is it?





I’ll give you hint.  Bull's-eye shooters know better than to store this in oak boxes or this happens.


It’s a badly corroded lead .22 bullet.  I took the photo at 35X with a Scanning Electron Microscope to show the crinkly surface.  It’s lead carbonate.  It should be metallic lead.

.
This one is in great shape.  I can even see my reflection in the bullet.

So what happened to this happy-go-lucky little .22LR?

As Ricky use to say “You got some ‘splainin’ to do Lucy!” 
But I’ll let the Navy conservators do it for me:   

“The chemical process is: Acetic and some other acids, in the presence of carbon dioxide, (in the air) catalyze with lead to produce lead acetate and lead hydroxide. Lead acetate and lead hydroxide together react with carbon dioxide and form lead carbonate. Lead carbonate then releases acetic acid and the process becomes self-sustaining.

I used to hate those ads for genuine Civil War battlefield bullets.  The ad shows some featureless blob of white, shaped like a bullet.  It may have been a bullet and it may have come from a Civil War battlefield, but what you’re really buying is a mixture of lead carbonate/hydroxide shaped like a bullet.  I’d be surprised if there was any metallic lead present.

Now I just smile at the idea of collecting lumps of a crumbly mineral.

Let’s let the Navy conservators explain:
“It is important to recognize that the formed lead carbonate is not just a substance clinging to the surface of a casting, it is the surface of the casting transformed to powder. For practical purposes, a portion of the lead is gone and lead carbonate is left in its place. The lead carbonate releases acetic acid which can continue the process until the lead part is progressively consumed from the outside, inward.”

.22 Lr corroded bullet from Thunderbolt
The early stages of lead carbonate formation.  Too late to save, the bullet has changed dimensions.

The resulting salts have lower density than the lead, so the bullet diameter increases and in very short notice the cartridge jams at the chamber mouth.  So you can't even plink with them.

Modern .22s aren’t shipped in wood, so where does the initial exposure to acetic acid (AKA vinegar) come from? 

It’s not only vinegar but other acids as well.  Conservators have identified some of the possible sources in today’s packing:
  • white glue
  • contact cement
  • silicone adhesives (some)
  • low quality paper and cardboard
  • vermiculite
  • soil


So where did the initial exposure come from that started this downhill slide?  I suspect the cheap cardboard box, the sizing, or the adhesive emitted acid vapor.  Of course it could have also been a quality issue and the lead bullet missed some step in the manufacturing process.

Since the process is catalyzed by vapors, one bad bullet will, in time corrode all the ammo in that box.  Naturally you want to remove any rounds with any sign of white on the lead bullet.  The Navy hasn’t found a cure yet, so I doubt that wiping lead bullets with an oil rag will solve the problem.  A thin coat of wax might work, but don’t get it so thick the rounds will fail to feed.

One solution is to buy nothing but copper jacketed rounds.
Ammo prices are still high.  I’ve seen 50-round boxes of .22 shorts selling for $30 and the vendors sell out of them.  Where’s all the ammo going?  The government says “Not us!”, if you believe them.  I suspect people are hoarding in the event of civilization’s collapse. 

If you are burying ammo and guns in PVC tubes, surplus ammo cans, wooden boxes or old shower curtains you should be advised that all your lead ammo could become useless.

But that’s another topic for another day.

I was cleaning up and found a polished cross-section of an armor piercing .30 cal bullet from a .30-06 cartridge made in 1943. (The cartridge, not the polished cross section.) I had forgotten about this little gem.  I’m not sure why I was making it.  I guess I was thinking of homemade Christmas presents for some of my shooting buddies.  But I didn’t like the way it turned out.

polished cross section of 30-06
The mount uses a clear thermo epoxy and a layer of black thermo epoxy.  The white patch to the left of the bullet is called a cloud.  It's unfused clear media.

It’s damn big compared to SS109 in .223.

cross section of SS-109 in .223
SS109.  It only looks big due to the magic of photography.

I found it interesting the bullet seems very symmetrical around the long axis.  The SS109 has what looks like an area of asymmetry what would introduce wobble.  The .30-06 also has a little base cap of copper over the lead and that looks like shoulders supporting the steel core.

Tip of 30-06 cross section of armor piercing  bullet
Tip of .30-06.  Note the bright
steel core above the dull lead.



.30-06 armor piercing bullet base
The bullet has a small copper base locking the lead core in place.

 


It looks like in 1943 they had some concerns about keeping everything centered and symmetric.  But then again the M-1 Garand had a claimed effective range of 500 yards.  Any imbalance in the bullet could results in a miss.

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