Depriming with air?

[hdwhit]

In the last couple of weeks, some members have shown automated decapping machines they built. They were truly impressive devices and I mean no criticism in the questions that follow, only to suggest an avenue for additional exploration.

What I noted with the decapping process used replicated what reloaders normally do on a press; to shove a pin through the flash hole to mechanically knock out the primer. My concern is 1) what about those oddball cases with smaller than normal flash holes that might bend or break a normal decapping pin, and 2) what about Berdan cases?

In order to not have the automated process fail because of either oddball flash holes or Berdan cases, it seems that someone using an automated machine would need to inspect their brass before using the machine to avoid stoppages. And then I wondered whether those concerns might be able to be addressed by forcing the primer out of the case using compressed air rather than a pin.

• Has this been tried before?
  
• If so, was it successful?
  
• What are its limitations?

I didn't want to build an experimental apparatus to answer these questions if the work had already been done and the process determined to be impractical for sound reasons.

Thanks for any information you can provide.

 

[HankC]

Primer hold at 50K PSI chamber pressure, but there is firing pin behind it. I guess it will still take some pressure to blow it out.

 

[jmorris]

On all my automated presses and machines I use a slip style collet to hold the decapping pin. So it moves up if obstructed instead of breaking off.

One could decap with air though, it would take a lot of pressure though as the area of a primer is tiny.

 

[jmorris]

They would certainly come out well before 50,000 psi though. The reason they stay in there is the same reason the case doesn’t blow into bits, there is steel keeping it in place.

 

[maxxhavoc]

I have not used air because it is inefficient. Air compresses too easily. I would guess you would need PSI in the thousands to do this.

I have used water. Basically,
-Get the case on a shellholder or other device that gives it a solid base, but has a gap for the primer to come out.
-Find a screwdriver/punch, or whatever that will go EXACTLY in the case mouth.
-Fill the case with Water
-Smack the screwdriver with a hammer.

If you do not use a case gauge or some other method (pressurizing the outside of the case the same as the inside) the brass will bulge. If the cases are WWII 8mm with staked and glued primers, they will bulge a lot.
If the water coming out of the case neck at pressure hits your hand, it will cut your hand. I did this, it only cut in about 1/8" - maybe less. Enough to bleed, not enough to do anything other than wash it with alcohol. It hurt, but it was cool. Worth it. I wore gloves after that.

Here is a video to demonstrate what I talked about. This makes it look easier than it turned out to be with WWII-era military ammo.

 

[jmorris]

The SI part of PSI is the important part, in this case. Like the thread where I was testing how much pressure a bullet being seated would creat inside the case and what it would take to get it to move under pressure. A .452" bullet has a radius of .266, for an area of .160, X 130 psi = holding against 20.8 lbs of force trying to push it out, unsuccessfully.



A small primer has around .025 area so with 130 psi you would have about 3.5 lbs of force on it. 1000 psi would be 25 lbs.

I just took a fired case and put it on top of a nut, place both on a scale and pushed down on a decap die while watching the scale. The primer popped out right around 60 lbs, it would have taken about 2400 psi to apply that much force.

 

[hdwhit]

jmorris wrote:
They would certainly come out well before 50,000 psi though.

Yes. But that is a fundamental misunderstanding of what air pressure is.

In a benchtop test, I was able to get non-crimped primers to start to move at 120 psi with a slow acting valve. I couldn't get crimped primers to move at all.

 

[hdwhit]

jmorris wrote:
I use a slip style collet to hold the decapping pin. So it moves up if obstructed instead of breaking off.

Yes. But it still stops the process since once the decapping pin moves out of the way it will no longer decap further cases until the process is stopped and it is re-set.

 

[jmorris]

In a benchtop test, I was able to get non-crimped primers to start to move at 120 psi with a slow acting valve.

Unless they were loose I don’t see how 3 lbs of force could remove a primer. If you have 120 pounds per square inch of pressure acting on .025 square inches, that’s all the force you have.

Now you could use a pneumatic cylinder with a larger piston that is attached to a decapping pin that would be effectively the same thing as a spring, that would normally decap unless it hit something then allow the decapping pin to move out of the way without being destroyed. That said, you still want the machine to stop, so you can get rid of the offending case or down the line you are going to have problems with the same case. Like trying to stick a primer into a case that still has a primer in it.

 

[doubleh]

It appears to make something really simple more expensive and complicated.

 

[jmorris]

Just so we are on the same page, you are talking about sealing something to the case like this rubber tipped blow gun and appling 120 psi and the primer moved?

 

[sbwaters]

Not sure I want to propel lead dust into the air I breathe.

 

[muleman11]

The primers would be leaving the cases at a very high speed. Like shooting yourself in the foot.

 

[WestKentucky]

Initial thought...why would anybody want to take the loose primer problem we all “love” so much and amplify that by using air pressure to knock it loose?

 

[Jim Watson]

Back when there were enough British shooters to support a small handloading industry, not just imports from the Colonies, there were some novel means of decapping, largely to handle Berdan primers. Nothing suitable for mass production, though.

 

[Fine Figure of a Man]

Decapping pins cost 2 or 3 dollars and I rarely break one.
Sounds like a really complicated fix for a non issue.

 

[buck460XVR]

The primers would be leaving the cases at a very high speed. Like shooting yourself in the foot.

^^^This......

Decapping pins cost 2 or 3 dollars and I rarely break one.
Sounds like a really complicated fix for a non issue.

^^^......and this.

While it may be feasible, would it be any more efficient or faster than what us home reloaders use now? Would one still still have to put each case in a shell type holder and lower some form of ram into it? Wouldn't one also need a noisy and costly air compressor in the reloading room? Would the decapping still be able to take place on a standard press or off press at a special dedicated decapping station?

 

[mdi]

FWIW; primers do move with pressure from the powder charges. In a revolver, the primer moves out of the pocket, the case moves back when pressure drops some and reseats the primer...

 

[jmorris]

You dont even need pressure from the powder. Load a primer in an empty case and drop it in your revolver then fire the primer. It will be moved back out of the pocket, if the flash hole has not been drilled out.

From what I am gathering the op is thinking about much less pressure than powder or even a primer can develop.

 

[rsrocket1]

The hydraulic method for Berdan primers is much better and safer than 2400 psi of compressed air. Once the primer exits the primer cup, the piston for ramming the hydraulic media prevents the incompressible fluid from shooting out of the case. A pneumatic decap will want to shove that compressed 2400 psi gas out somewhere.

Much better to simply buy a handful of extra decapping rods or replacement pins.