Why do primers back out when firing just a case with primer?

[Rule3]

I broke apart a few 44 mags. Removed bullet and powder.

Put the primed case in my 629 and ignited the primer. The primer backs out enough to jam up the cylinder.

I mentioned this in another post and Bruce said it's normal. My question is why? Is it because there is no back pressure or what?

Also, for the poster(silvercn) that was concerned with lead. I fired three of these and my barrel and forcing cone were filthy. I ended up cleaning my gun as much as if I took it to the range. I could not believe how much "crud" a few primers could create!

 

[jepp2]

All the gases from the primer burning must rush through the flash hole in the case. It generates enough pressure to back the primer out of the primer pocket.

This happens when you fire a loaded round also. But in that case the pressure from the burning powder forces the case backwards against the recoil shield, thus reseating the primer in the case.

You didn't have the reseating action by just firing the primer. Folks that shoot the reusable rubber bullets wind up drilling out the flash hole larger.

When I need to remove live primers, I slowly deprime them using a universal decapping die. I wear eye protection and gloves, and I have a piece of PVC pipe cut to slide over the cutout area of my Rock Chucker ram. I'm not suggesting you do this, but I haven't ever had a primer go off. But I am always prepared just in case.

 

[ms]

I think the primers normally back out, and if it is a fully loaded cartridge they get reseated when the case pushes back against the recoil shield.

I remember reading that if you open up the flash hole the primers won't back out, so it's handier if you shoot wax or plastic bullets with just primers.

 

[Iggy]

Normally the case would be forced against the recoil shield when you fire a loaded cartridge. This would then force the primer back into the case

Again, a normal cartridge with a powder charge would have a fuller ignition and burn out most of the residue that comes with just firing a primer.

Looks like MS is a faster typer than me.*G*

 

[Rule3]

Thanks all. that sounds like the ticket.
Iggy, did not think of that (amongst many other things) Yes the powder burning must burn up the primer charge.

I have deprimed many live primers but did not have the 44 dies in the press and did not want to change out as I am loading 45's.

Kinda like being a kid again with a big arse cap gun!

 

[Titegroups]

If the whole case comes back when fired with a regular charge would the primer even move or have the chance to move? I guess maybe the differential in time between the primer firing and the powder in the case igniting would give it a chance to move first. Would be neat to see some macro high speed footage of that.

 

[Skip Sackett]

Yes, no pressure to make them flat with the case.

 

[cjw3]

As others have said, firing a cartridge in a revolver re-seats the primer.

Several years ago, I used to make up primer-powered wax bullet loads for fast draw practice. The flash hole had to enlarged so that the primers would not back out. The cases were kept carefully segregated from unmodified cases.

 

[silvercn]

I broke apart a few 44 mags. Removed bullet and powder.

Put the primed case in my 629 and ignited the primer. The primer backs out enough to jam up the cylinder.

I mentioned this in another post and Bruce said it's normal. My question is why? Is it because there is no back pressure or what?

Also, for the poster(silvercn) that was concerned with lead. I fired three of these and my barrel and forcing cone were filthy. I ended up cleaning my gun as much as if I took it to the range. I could not believe how much "crud" a few primers could create!

Prior to all this discussion I would have never known primers have a lead discharge too.
In hind-site it just makes good sence.

 

[Rule3]

Yes, lots of nasty stuff in the primers. It literally took me 4-5 patches to clean the barrel and bore of my 629 after firing only 3 primers. They were filthy dirty, not just a little bit.

"Primer and ignition compounds for small arms are known from AT-PS-370 403. These compounds contain heavy-metal salts of aromatic nitro compounds. Such primer compounds generate injurious gases, particularly if used in closed rooms for training purposes.

Other initiating explosives known in the prior art, containing such heavy metals as antimony, barium, lead, mercury and the like, are no longer wanted today because of their emissions and residues in firing ranges. The same also holds true for zinc-containing pyrotechnical compounds. On the other hand, organic nitrogen compounds known to be used as initiators, such as diazo compounds, triazoles, tetrazoles or the like, are objectionable because of their carcinogenic properties, which applies both to the primer substance and to its decomposition products."

Scroll down to primer chemistry:

http://en.wikipedia.org/wiki/Centerfire_ammunition

 

[SmithSwede]

To answer the above question---yes, generally speaking primers always back out first, and then they get re-seated as the main charge forces the entire cartridge case back over the primer.

John Garand actually used the movment of the primer to actuate his early rifles.

Garands primer-actuated mechanism? [Archive] - BayouShooter.com Forums

If you drill out the primer flash hole larger, they won't set back. I suppose it is also possible that primers can be crimped in such a way that they don't set back.

 

[laney566]

All the gases from the primer burning must rush through the flash hole in the case. It generates enough pressure to back the primer out of the primer pocket.

This happens when you fire a loaded round also. But in that case the pressure from the burning powder forces the case backwards against the recoil shield, thus reseating the primer in the case.

You didn't have the reseating action by just firing the primer. Folks that shoot the reusable rubber bullets wind up drilling out the flash hole larger.

When I need to remove live primers, I slowly deprime them using a universal decapping die. I wear eye protection and gloves, and I have a piece of PVC pipe cut to slide over the cutout area of my Rock Chucker ram. I'm not suggesting you do this, but I haven't ever had a primer go off. But I am always prepared just in case.

I prefer turning my head away and squinting real hard
Kinda like when you open a can of buscuits!!