Why are my primers flat?

[Northman999]

Fellows,

I hit the range today and after firing a box of factory ammo (Federal Power Shock 150gr powerpoints) through my Garand I tried some of my recent handloads (165 gr Accubonds, 48.3 gr IMR 4064, Federal brass, Winchester primers, for 2700 fps). The fired smoothly and seemed to be less "snappy" than the factory stuff, brass was not thrown any further than factory 150's, and cycled flawlessly. After three rounds I inspected my brass and was surprised to see my primers were flat. Now a note about these primers, this is my first time using these primers and I noticed when I reloaded that the seat VERY easily and in fact seat deeper than factory ammo, or other primers I've used. They weren't falling out or anything and the deeper seat seemed cool for a military semi auto to minimize the risk of a slam fire, so I really wasn't concerned. My load is not a "hot" load and is 150 fps slower than factory 165's in Winchester Silvertips or Failsafes. I suspect that the flat primers are due to the primers themselves, rather than a sign of pressure, which I would normally think. Here are a couple of pics, unfired on left, fired on right.

So...what do you guys think? Is this something to worry about or do these primers just do this?

 

[Eagleye]

I don't see anything there that would cause me concern. The new Winchester primer (like the Remington) is bare, no nickle plating, and is a tiny bit smaller in diameter than the plated ones were. Thus they tend to seat easier than did the older type. Additionally, I have found Federal brass to be a bit "softer" in the web area than is Winchester, making primer pocket expansion a reality, even with loads that are not overpressure. Regards, Eagleye.

 

[Northman999]

Thanks Eagleye!

 

[TRG-42]

As already mentioned nothing to worry about in your case .

Problem with Primer Reading as Pressure Sign

Although a overly flat primer generally indicates a problem with pressure it is sometimes NOT the case

What you are experiencing is most likely caused by the following :

You have a Garand, which will have a genereous chamber and possibly headspace on the long side .

When the firing pin strikes the round, it is driven forward to headspace on the shoulder. If your headspace is excessive , it gets driven forward a significant amount

Round goes off. Primer gets pushed BACK out of pocket to contact bolt face ( if you dont think this happens you have never fired a primed brass in a revolver. It can lock up your cylinder ! ) .

At this point the case has gripped the chamber walls . Recall, case head is forward from bolt face, primer pushed out to contact bolt face

As pressure builds case head gets driven back to bolt face. This is where the "flat looking" primer CAN come from even with moderate case pressure. The primer has already swollen from the pressure and again, recall its unsupported slightly since its been pushed out of the pocket

As the case head contacts the bolt face, the primer pocket gets "filled in" by balloned out primer as it forces the the primer back into the pocket

This can make the primer look very "flat" even with moderate pressure . Most load books such as the Speer describe this in better detail than I can

BTW - it is this phenomenom that causes case head separation. The case gets driven forward ( by firing pin ) to headspace on the shoulder. As pressure builds, case grips chamber walls ( that is why you dont lube your chamber ! ) , then expands in length as case head contacts the bolt face. Because the case has gripped the chamber, the location the case stretches is just above the case head. that causes thinning of the web and eventually case head separation. Case head separation is generally a sign of excessive headspace

This is why neck sizing when appropriate doesnt hurt. There should be no thinning in this region because your case is the perfect fit before firing

Cut a case in half to see if there is any thinnning just above the case head

A final BTW, although Fed brass tends to be on the soft side , an enlarged primer pocket won't really contribute to the problem you are seeing there. I had a bunch of test loads were half the brass had VERY loose primer pockets...don't ask ! They were Wby brass so I wanted to get one more firing for load testing . There was no diffrence in primer appearance between the embarassingly loose primer pockets and tight pockets.

 

[Northman999]

Thanks for the informative answer TRG-42. I'll save this page in my "reloading info" archive for future reference. You guys are a gold mine of info!

 

[CanAm]

Soft primers. The PMC Russian primers do the same on my 303 reloads.

 

[stocker]

If you look at the freshly primed case in the photo you will see that the primer is seated quite deeply as it probably should be for a semi auto. Whether it's head spaced a bit generously or not gas pressure is going to get the primer moving backwards quite sharply and it will impact the bolt face hard enough to cause that degree of flattening. I doubt you have a problem with the primer itself.