Converting berdan cases to boxer

Posted by on November 29, 2011

My last posting was about priming with berdan primers.    Willie Barnard posted a reply that explains a simple method of hydraulic decapping that he devised, which avoids the need for a lathe turned punch.    The only downside, if it can be called that, is that the pistol case must fit the rifle case within fairly close limits, so it might not work with all calibres.    But then, there are not many berdan primed calibres these days, only the 7.62 NATO and possibly some 5.56NATO.    It is a simple and clever method, and shows what can be improvised when the mind is applied.

Converting berdan cases to accept boxer primers is something done by very few reloaders.    Some of us, including Willie Barnard and I, do it for the hell of it, and because we don’t want to throw away good cases.    But generally, it is a survival measure that you do when you can’t get boxer brass.    In the nineteen seventies, when economic sanctions were imposed on South Africa, we had the strange situation in which boxer primers were imported sporadically despite the sanctions, but boxer cases were all but impossible to get.    It was therefore quite common practice to convert military 9mm brass to boxer.

At first sight, it is simple – you drill a central flash hole, at the same time taking off the berdan anvil.    It is easiest on a lathe, but works well (and faster) on a small drill press with a simple fixture to centre the case under the drill bit.   What about the existing berdan flash holes ?    Doesn’t matter, they are so small that they can be ignored.    A 2mm drill is suitable.    But the drill bit will wander when it contacts the anvil.    I found that a 2mm end mill works better – it machines off the anvil very neatly and drills the hole as well.

Somebody marketed a die that did the job a lot faster.    It looks very like a sizing die, for use in a loading press,  complete with what looks like a decapping pin.    But it isn’t a decapping pin, it is a hardened punch with a perfectly flat end.    In use, it is screwed into the press, and the case inserted into the shellholder,  just as for normal resizing.    The ram is brought up very smartly, and the “die” punches a 2mm hole through the web of the case, and removes the berdan anvil at the same time.    I have one of these – I have no idea who made them – Keith Dyer of Magnum magazine found two of them in a shop in Durban.    Apparently they had been lying around for years – nobody wanted them, so the shop gave them to Keith, who sent one to me because he knew I’d be interested.   I tested it – it works well – the hole it leaves is often a good bit off centre, but that doesn’t matter.   The hole is also ragged, but is easily cleaned up.       

Small berdan primers are 4.50mm (.177 inch) diameter, small boxer are .175, so the boxer primer is a loose fit in the berdan pocket.    In the 1970s the boys filled the gap with nail varnish.    I don’t think that’s too safe with a high pressure cartridge like the 9mmP, but a lot of it was done without trouble as far as I know.     What’s worse, though, is that boxer primers are thicker than berdan.   I measured a few of each, and the average was berdan 2.76mm, boxer 3.22.    Therefore, a boxer primer in a berdan pocket stands proud quite a lot.    It could prevent the slide of a 9mm pistol from closing fully, and I suspect that it was tolerated in a pinch, and that 9mm pistols are all military, with chambers that are generous enough for it to be gotten away with.    But I’m horrified at the idea of a slide closing on a primer standing proud of the case.    I have never heard reports of a problem in that respect, but, all things considered, I consider it a risky conversion to be done only when there is no choice.    

It is an even bigger risk with rifle because of the higher chamber pressures.    Large primers are even looser in the pocket than small primers.    It occurred to me that the berdan pocket could be machined deeper with an end mill ground to the right diameter, but the metal is already quite thin at that point, and would be dangerously thin if reduced by half a millimetre.

I know of at least one individual (a toolmaker) who made up some tooling for pressing something like a ring crimp around the primer pockets of rifle brass.    But it is not a crimp – it reduces pocket diameter for about one third of the depth.   It over-reduces it slightly, then it can be brought to the correct diameter for a boxer primer with a pocket uniforming punch.    That’s a neat way of doing it, but it doesn’t take care of the pocket being too shallow.   Maybe the guy has solved that problem too, maybe I should try to find him and ask.  

But until I get a satisfactory answer, I wouldn’t try the conversion – rather get some berdan primers.

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