Flattened Primers

[J.Johnson]

I am fairly new to reloading and have read some about flattened primers. Could someone please explain what exactly "flattens". I am confused. A picture of a flattened primer would be great if someone has one.

Thanks in advance.

 

[Jimbo357mag]

All primers will be flattened to a certain extent when fired in a gun. In the photo below you can see a good example of a normal primer on the right and an over pressurized, flattened primer, on the left. The softer, weaker, metal of the primer will flow to fill the primer pocket as the pressure increases.

...Jimbo

 

[GP100man]

To add to Jimbos response :

While primers do flatten it`s not necassarily a sign of hi pressure.

Take into consideration of the materials used (brass) thinner than the case at least at the case head .

Naturally if primers are grossly flattened it`s a sign of excessive pressure ,but when I`m going for MAX loads I use NEW cases & carefully measure casehead dia. this is a sure way to assese chamber pressures .

& I`ll never do it with out a chronograph again !!!!

 

[bowfishn]

In the past the only flatten primers I have experience have been Factory loads, and I tend to run my reloads hotter than the factory loads. Go Figure

 

[jforwel]

My .41mag reloads have been flattening primers for decades and I do not load up to max. A recent article in Handloader by Brian Pearce I believe, says that flat primers are not a good indicator of high pressures since the type of gun and brand of primer can be a factor with what happens upon firing.

 

[edfardos]

let me guess, federal primer on the left, cci primer on the right... Same pressure.. Both are good primers.

edfardos

 

[sourdough44]

I take flattened primers as one possible indicator of higher pressure, you have to take other factors into consideration. As mentioned some loads/guns may give you very flattened primers about all the time with factory loads. You often hear of Federal primers being rather soft.

I start with carefully measured charges and chronograph speeds as to where I am with a load, compared to 'book data'. Of course characteristics of the powder type have to be taken into account. As an extreme example H-110 gets to 1100fps much differently than the likes of Titegroup.

 

[Donaldjr1969]

JJohnson, for what are you reloading? Semiauto or revolver? A person will almost always get primer flattening with revolvers since the case will slam into the recoil shield after discharge. Since the primers are slightly blown out after firing, the re-seating of them on the recoil shield will serve to flatten them. For revolvers, sticky extraction is a far greater indicator of excessive pressure than a flattened primer.

Now I know that primers also strike the back of the bolt/slide on a semiauto before the bolt moves backwards and that too will reseat the primer and serve to flatten it as well. However, since the only semiauto cartridge I reload is 45Auto, a low pressure round, I have not seen primers in the condition seen after shooting even plinker level 44Mag loads. Obviously our members here that reload 9mm, 40s&w, 38Super, and other high pressure loadings will see some flattening as Jimbo's example illustrates. But for my 45Auto loads using WLP primers (as well as WSP in small primer brass), they all look like the right side example in Jimbo's photo.

In my opinion, unless there is perforation of the primer cup or "cratering" of the primer, flattened primers really do not tell too much of high pressures, especially in revolvers.

 

[anachronism]

Flattened primers are not a reliable indicator of excessive pressures under any circumstances. This is outdated information. There are too many possible variables from primer to primer, case to case, load to load, and gun to gun.

 

[WESHOOT2]

By the time a(ny) primer REALLY flattens I'm well-and-WAY past safe maximum pressure.

I 'read' primers like this: If the primer has fully flowed in its case pocket, right out to the edge (or over) I consider it "flattened".

Except I've observed "flattened-n-flowed" primers in loads nowhere remotely near "max".

 

[J.Johnson]

Thanks for all of the responses guys. Lots of good info.

 

[Jimbo357mag]

Flattened primers are not a reliable indicator of excessive pressures under any circumstances. This is outdated information. There are too many possible variables from primer to primer, case to case, load to load, and gun to gun.

When working up loads in any gun I always look for flattened primers. It is not the best indicator of pressure but it is one indication. When working with the same components it is possible to see some differences in the appearance of the primers. When you take velocity, recoil, case extraction, carbon on the sides of the case, smashed printing on the case heads, POI, group size and several other factors into account you can get an idea of the pressure without a copper crusher barrel or strain gauge. 8) 8)

...Jimbo

 

[anachronism]

Flattened primers are not a reliable indicator of excessive pressures under any circumstances. This is outdated information. There are too many possible variables from primer to primer, case to case, load to load, and gun to gun.

When working up loads in any gun I always look for flattened primers. It is not the best indicator of pressure but it is one indication. When working with the same components it is possible to see some differences in the appearance of the primers. When you take velocity, recoil, case extraction, carbon on the sides of the case, smashed printing on the case heads, POI, group size and several other factors into account you can get an idea of the pressure without a copper crusher barrel or strain gauge. 8) 8)

...Jimbo

I feel you would be better off measuring case head expansion.

 

[Jimbo357mag]

I feel you would be better off measuring case head expansion.

That too. :D :D

...Jimbo

 

[DHB]

One other thing. Depending on what weapon you are shooting, a primer can also back out, In some of the single shot rifles (original more so) the primer sticking into the firing pin hole can make the weapon inoperable. In some cases it is just the firing pin/hole is too big, and the primer flows into the firing pin hole. Thus stopping the weapon.

 

[BearStopper]

I have seen a 22-250 in a Mauser action that grossly flattened primers loaded at standard pressure...caused by an incompetant gunsmith that removed and replaced the barrel and did not bother to properly set the headspace. Pushed the shoulder of the brass forward what appeared to be almost an 1/8th inch. On a revolver I have never had any hint of it even on 44 magnum.