Norma 9mm Brass

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Interesting Problem -

I'm reloading 9mm's last week for a Saturday match on my Dillon Square Deal press and "Wham!" The handle comes to a dead stop. I check all the stations and nothing appears wrong and again "Wham", dead stop. I suspect that it is the decapping and resizing station. I take out the empty case and move the handle through the remaining stations with no problem.

I examine the empty brass case. It's a Norma brand otherwise appears normal. I try another one, no go, another one no go, a Federal, no problem, Winchester no problem, Blazer, all good. Another Norma, again no go.

Apparently the primer hole in Norma 9mm brass is a bit smaller than all other commercial brands, military too. My decapping pin will not enter the primer hole.

I looked close to make sure it wasn't Berdan primed but it only had the single hole in the middle. A smaller that usual hole. This was brass recovered from an indoor range. I've never used Norma 9mm ammo so I don't know what the box might have read.

Anyone else had this problem? Anyone know the reason?
 

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I know on some rifle cases, a smaller flash hole is desired. Not sure why.

You can buy dies with thinner decap pins. Honestly, if it was me I'd be tempted to use the decap pin and force it through the hole to enlarge it, then use a primer pocket tool to make sure the bottom is flush. Or just chuck the cases...

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I have resized some norma 9mm brass no problem, what dies, Dillon I presume? I use a lee universal decapper, and a hornady sizer. neither ever had problems with the flash hole size.

can you put calipers on your decapping pin to see how large it is? I'm doing some reloading tomorrow, and will check my decapping pin sizes.
 
There are two common flash hole sizes: 5/64" (0.078125") and 1/16" (0.0625"). The metric countries typically use 2 mm (0.07874") for the large hole and either 1.5 or 1.6 mm (0.0590" or 0.0630") for the small hole.

There are a couple of theories as to why a small hole should be superior. The one I always heard was that because primer blast wave pressure vary over 10% within a lot, the use of the smallest primer with the tightest constriction would cut down the primer influence on peak pressure, leaving it to the powder charge to present the dominant error term. Another theory mentioned in this paper is that the narrower hole lengthens the "spit" of flame and sparks and extends its duration and gives a couple of explanations for why that could be good in the middle paragraph of the literature review on page 26.

Incidentally, that second paper, written as a Master's thesis by an explosives engineering student, has a number of interesting things in it. These include a theoretical explanation of SEE (secondary explosive effect, aka, detonation) and good pictures of a universal receiver and pressure test barrel setup at Fiocchi's lab, and a description of using Excel for the statistical interquartile range method of determining whether a data point should be eliminated as an outlier or not. The author found hole size and whether or not the hole is off-center does affect group size. His finding is that there may be an optimum flash hole size, but that it is a little bigger (3 mm or 0.118") than the standard ones are and that the theoretical advantage of the small flash hole does not pan out in performance measurements.

Everyone scampering to get a 3 mm drill bit yet? I wouldn't jump on that without sacrificing some to experiments in my own guns because of the usual warning: YMMV.

Note there is an error in table 3.5 on page 76, where he highlighted the wrong column. I copied his data into Excel and double-checked this, and the highlight should have been added one column to the right.
 
Thank you all for this interesting (and new to me) information. I've reloaded 10's of thousands of 9mm's over the last 25 or so years on Dillon Square Deal or 550 presses and this is the first time I've ever seen or heard about two different size primer holes. Since the Square Deal uses proprietary dies, I emailed Dillon to see if they might have a smaller decapping pin. I'll let you know if I receive a reply.
 
You can take the larger decapping pin, chuck it in a drill and take some fine sanding cloth and in a few seconds have a .0625 decapping pin which will still work on the larger flash holes. Just keep one of the cases handy when sanding it down and check every few seconds until it passes freely through the flash hole
 
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