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Discussion Starter · #1 ·
Made a tool for reloading because I needed some practice on my lathe and I finally decided to start keeping and prepping berdan cases in 7.62x39, these yugo ammo have some very nice brass, its a waste to scrap them.

I have looked into the RCBS berdan decapper, but it seems to be a crap shoot. not to mention a good way to put extra deformation to the case neck.
I have also looked into hydraulically deprime berdan cases, and while it seem like it works, the common method of puting a punch down the case full of water leave something to be desired, its very messy, possible water splashing back into your face, pin striking the bottom of the case with heavy hammer blow, also possible deformation to the case neck.

then I saw a video of someone machined a round bar with 2 holes and rod to push the water, while it work it still splashes water everywhere. so I took that basic design and make a few changes.

I made the plunger/piston have pretty tight clearance, pretty tight for the application. added a o-ring. that took care of the splash back, added a relief channel on the bottom so the water will shoot forward.

added knurling for my butterfingers so I don't drop the tool when handling. first time knurling, does not come out too good, but it works.
drop the case in head first, fill with water, insert plunger, place on sturdy surface and hit with a BFH. primer will come out with great force.

I think I might make an insert out of stainless steel for it so I can make and use a smaller diameter plunger for reduced operating effort. that way its easier to use it with out having to hammer on a sturdy surface, just free hand.

















 

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Great idea.
I have been using the RCBS Berdan decapper for years with no troubles. I usually knock out between 500 and 1K at a time with very little effort. Once you learn how to set the pin in the primer indent just right, you have is made.

Semper Fi
Art
 

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I may have to give this a try. I have several thousand cases. I tried making the one pin punch tool. I found it very ineffective.

To improve your knurling look. Go both directions. Slow spindle speed, high feed rate, plenty of oil. Put a small undercut at the end of where you want the knurl and let the roller go past it slightly, reverse the feed direction without disengaging the feed, (spindle off when changing direction GI3) I don't see the knurling tool, but investing in a scissor type knurling tool may be worth considering. When knurling smaller diameters the part may push away giving uneven looking knurls. Not an issue with the scissor type.
 

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Nice work and clever idea. Still seems like an awful lot of effort to deprime them though. Plus I can't recall when I've ever seen Berdan primers for sale. I've tossed thousands of that beautiful Danish AMA 30-06 brass in the scrap bin because they were Berdan primed.
 

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Discussion Starter · #6 ·
Thanks for the knurling tips MemphisMachinists, I need to look into a scissor type knurling tool.


M14E2, powder valley and a few major reloading supply shop have berdan primers.


I think I might have to build that insert, I look at the tool again, the plunger surface area to the primer surface area is a good 4:1. going to try to get it down to at lease 1:1 that would require much less force to hammer out the primer.
 

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Nice work and clever idea. Still seems like an awful lot of effort to deprime them though. Plus I can't recall when I've ever seen Berdan primers for sale. I've tossed thousands of that beautiful Danish AMA 30-06 brass in the scrap bin because they were Berdan primed.
You can find Berdan primers online if you're persistent. Grafs has some from time to time, as do some others whose names temporarily elude me.
 

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Looks like a nice setup
 

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I saw some Berdan large primers the other day at the gun show. They were Wolf brand. I don't know the Berdan primer sizes but it looks like they have large and small and these were the larger ones. I didn't ask the dealer about them though as I've got a 1,000 for my SA .308 cases I bought a couple years back.
 

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Generally speaking the following Teeth Per Inch (TPI) specs are considered common;


  • 8 - 24 = Coarse
  • 25 - 48 = Medium
  • 49 - and above = Fine

The key to a good knurl is the relationship of the diameter of the part to the circular pitch of the knurling tool. The circular pitch is the distance between the points on the tool. You can find the circular pitch by either measuring the distance between the points or by dividing the TPI in to the number 1. Dividing the circular pitch of the knurling tool by pi (3.14...) produces a constant for that knurling tool. The part's diameter should be an even multiple of the constant for the best results.

If you divide the diameter of the part by the constant and you get an even number then the knurling should come out perfect. If the result isn't an even multiple then will need to turn the stock down a thousandths of an inch or two in order to get a good knurl. You can use this method to calculate what diameter the part needs to be; If you have a 12 TPI tool then

1/12 = .083 which is the circular pitch.

Now divide the pitch by Pi

.083/3.14 = .0265 which is the constant for a 12 TPI knurling tool

So let's say that you have a piece of stock that you want to finish with a 12 TPI knurl, and you know that it will have a finished diameter of around 1", you can figure out what diameter it needs to be before you try knurling it. Start by dividing the approx. finished diameter by the constant,

1/.0265 = 37.736

Now you know that the part must be somewhere between 37 and 38 times the constant value.

37 x .0265 = .9805
38 x .0265 = 1.007

So the part needs to be finished to a diameter of .9805" or 1.007", depending on whether you choose to have it slightly under or over 1".

Don't forget, the part can be slightly under or over the mathematically perfect size by a few thousandths and still turn out well so the 1.007" diameter might only need to be 1.003" and still work.

Other than that, clean the chips off as you go and brush the knurling with a wire brush after you're done and it should look pretty good.
 

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Awesome! Thanks for the in-depth answer. I'm not a machinist, so in the past I just ran a knurling tool into the work and got something that resembled knurling, but never gave it much though beyond that. The notion to start with a part that has a circumference that is an integer number of knurls in length is completely obvious .... so obvious that when it was staring me in the face I never saw it.
 

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Discussion Starter · #16 ·
Been pretty busy this week, made some changes yesterday, but its a fail.
Took some advice on using alcohol cutting the aluminum, works great.
also took the advice of roll the knurl back and forth, comes out much better, but thats just the width of the rollers. still need to invest in a scissors type.
the piston size is much smaller now to exert more force on the output surface(primer) but at the same time it pushes the cylinder out of the body with such foce that it compress the outer edge of where that steel retaining disc sits. I probly need to make a wider main body that will support the whole disc, or make the body out of stainless like that disc.
but I could never get good finishes on the 303SS on my mini lathe. maybe i need to see if I can tighten the carriage as i think it tilts when under heavy load.









 
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