Ammo

Gumbo can be assembled from a lot of different ingredients. You can add a lot of things (some not really indentifiable) and still have gumbo. The varieties are endless, and you really have to work at it to screw things up.

Not so with reloading. Reloading handgun calibers, especially. Shotshell reloading is an absolute recipe; you assemble exactly the components called for in the book. Rifles and handguns give us a little leeway, but if you go too far afield you can find yourself in trouble. This is the tale of how I managed to blow up my Colt Delta Elite 10mm not once, but twice. I will omit certain details because the lesson is not in the details, but rather in the details ignored. I was working as a gunsmith while reloading huge volumes of ammo for competition and practice. My customer came to me with a 10mm problem His gun didn't work reliably with his new load, and, in his last practice session, he blew a case. The pistol (an S&W 1026, the very definition of stout) was unharmed. The magazine was toast, and he was unharmed. Could I help?

So I take his ammo, review the loading data and pack it for the range. His load data lists a modest dose of a relatively fast-burning powder over a normal-weight bullet. The charge doesn't seem out of line for that class of powder. Length is good, crimp looks fine, and I even pull a bullet and weigh the charge—just as listed on the box.

I take the ammo and my Delta and set up the chronograph. The first four shots show average 721 fps. A little slow for what he needs and what might be expected, but the extreme spread? Well over 400 fps. A low of 509 and a high of 953. I don't know the five-shot average because the fifth blows a case head, the bullet hits my skyscreens and the chronograph quits.

Back at the shop, I find my Delta is unharmed except that the magazine's removable baseplate was blown off. The chamber headspaces correctly; the extractor tension is correct.

I head home and pull out my 10mm dies. I load five rounds, duplicating the load while individually weighing the powder charges. At the range once again, I get a two-shot average, as the third shot blows a case.

So I then do what I should have done before. I look in all my reloading manuals, and none of them lists that particular powder for use in the 10mm. Most significantly, the reloading manual published by the powder maker does not list that powder of theirs as used in 10mm load development. In statistics, there are two terms you need to know extrapolation and interpolation. Extrapolation is extending data. "If I save $20 a week, in two years I'll be able to afford a Carribean cruise." Interpolation is estimating performance between data sets. If you know that five grains of powder gets you 900 fps, and six grains gets you 1,100 fps, then interpolation tells you that 5 1/2 grains gets you 1,000 fps. Here's the trick to both You can only estimate in one variable at once. You can't do a two-variable extrapolation. "If I save $20 a week, and I find a cute girlfriend, then I have a really fun cruise" doesn't work.