Primers expand in diameter upon firing - how much is normal?

[JimGnitecki]

I am trying to find a way of assessing RELATIVE peak pressures for my 9mm 115g loads, wondering if the peak pressure varies a lot with COAL changes over a range of about .015".

I found an online article that speculated that primers do indeed grow in diameter upon firing. The article looked at "9 Major" loads since that would accentuate any growth. The testers used Federal Gold Medal small pistol primers (like the ones I am using) for their testing, as they asserted that the Federal GM primers are softer than most and so show more diameter growth.

The testers said that the unfired diameter of an unfired Federal GM SP primer is .1745". My digital caliper agrees.

The testers found that the diameter grew for many 9 Major loads, to about .178" or .179", and to as much as .180 to .183" or so as I recall, for the hotter loads.

I amusing 8.0 grains of Vihtavuori 3N38, which is almost exactly in the middle of the VV load table for the bullet and powder I am using (The range in the table is from 7.2g to 8.7g). And my muzzle velocity runs from high 1200s to about 1324, depending on the COAL I use, where VV says that the predicted muzzle velocity for the 8,.7 g load is 1401 fps. So far so good.

So imagine my surprise when I found that the vast majority of my fired primers in my Dillon primer catcher were indeed in the .1745" to .1775" range, BUT a handful of them (4 out of about 50) ranged in diameter from .1800" to .1820"! Could this be the result of that COAL variance that I have been posting about recently in my other current thread, where the COAL was varying up to .010" (ultimately traced to bad combination of bullet shape and die bullet seating insert) ?

Those larger OD primers MIGHT have occurred when I was targeting a 1.142" COAL, before I discovered the magnitude of the COAL variance, and so moved my target COAL length upward to stay longer than the minimum COAL length in the Vihtavuori load table. But I cannot be sure, as the primer cup on the Dillon XL750 is not "first in & first out"!

Here's a photo of the 4 primers:



Thoughts?

Jim G

 

[Dale Alan]

Did you measure the primer pocket diameter before firing ?

 

[fxvr5]

Link to the article?

 

[fxvr5]

I amusing 8.0 grains of Vihtavuori 3N38, which is almost exactly in the middle of the VV load table for the bullet and powder I am using (The range in the table is from 7.2g to 8.7g). And my muzzle velocity runs from high 1200s to about 1324, depending on the COAL I use, where VV says that the predicted muzzle velocity for the 8,.7 g load is 1401 fps. So far so good.

To be clear, VV does not show 3N38 for your bullet, or its sibling the 115 grain XTP. You're using data for the 115 grain Berry's HB RN TP.

 

[forrest r]

Your fp is dragging

 

[bluetopper]

Never in my life have I heard anyone measure a primer after firing. The diameter would be directly related to the particular and individual brass it was sitting in, not the chamber pressure upon ignition.

 

[Walkalong]

Old timers would measure rifle case head expansion to the nearest .0001 and compare it to factory ammo.

Our best bet with auto pistol ammo is to follow trusted published data.

 

[Blue68f100]

You would have to measure the primer pocket to 1/100000 of an inch to have a reference to know if any thing changed for every piece of brass. Which means every one will have to be numbered logged before and after, the same applies to the primer cap. I don's see that happening. If your expanding your primer pockets your yielding the brass under pressure. How much? The only way to know is with pressure equipment

 

[243winxb]

my muzzle velocity runs from high 1200s to about 1324,

BUT a handful of them (4 out of about 50) ranged in diameter from .1800" to .1820"

Expanded primer pockets from a pressure spike, using mid-range powder charges of slower then normal powder burn rate.

Note SAAMI velocity for +P loading.

VV says that the predicted muzzle velocity for the 8,.7 g load is 1401 fps.

Compared to SAAMI, if velocity is a sign of increased pressure, 8.7 grs is an over load? Look for high pressure signs , like expanded primer pockets after 5 firings or less.

 

[243winxb]

https://www.shootingtimes.com/editorial/ammunition_st_mamotaip_200909/100079

1. Pressure spikes may come from early bullet movement.
2. A starting load or mid-range may do better with a magnum primer.

Too Much Primer
You can have too much primer. When the output gas volume of the primer approaches that of the cartridge case, sometimes special handling is required. I remember when CCI was working with some experimental primers for 9mm Luger, and we started seeing odd time-pressure curves on the computer. Instead of the normal single peak, we saw two. One QA tech commented that it looked like the dual humps of a Bactrian camel.

It was a classic case of high gas volume but too little temperature. The primer's extra gas unseated the bullet while still trying to light off the main charge, producing one peak. Then the bullet retarded as it engaged the rifling, creating the second peak. Although a shooter would never notice this in a production firearm, that double hump was worrisome, and we abandoned that mix.

The powder you listed at 8.7 grs is a compressed load for the 115 gr Berry´s, HB RN TP. Not a good choice imo. Bullet or powder.

Watch for expanded primer pockets in 5 firings or less.

 

[fxvr5]

Note SAAMI velocity for +P loading.

Compared to SAAMI, if velocity is a sign of increased pressure, 8.7 grs is an over load? Look for high pressure signs , like expanded primer pockets after 5 firings or less.

SAAMI's velocities are 'nominal', aka typical. 3N38 is well known for producing very high speeds in 9mm and 38 Super within normal pressure limits. It's a favorite powder for IPSC/USPSA for this reason.

SAAMI's velocities are from a 4" barrel. The P210 has a 5" barrel.

I run 8.0 gr of 3N38 in 9mm from a 5" Kart barrel with 115 HAPs and get 1390 fps (at 1.100 OAL).

 

[243winxb]

I run 8.0 gr of 3N38 in 9mm

How do the primer pockets hold up? Getting more then 5 firings? Just want to learn.


The OP did pick the powder* , 8.7 grs that will produce the highest velocity, 1401 fps. .

 

[fxvr5]

The powder you listed at 8.7 grs is a compressed load for the 115 gr Berry´s, HB RN TP. Not a good choice imo. Bullet or powder.

8.7 grains of 3N38 with the Berry's bullet produced 1321 fps from a 4" barrel in this article:
https://www.shootingtimes.com/editorial/fast-9mm-loads/388612

3N38 is a superb powder for high speed in the 9mm and 38 Super. Berry's bullets, on the other hand, would not be my first choice (for accuracy) and I opt for something else in that weight, the 115 HAP being a very good choice.

How do the primer pockets hold up? Getting more then 5 firings? Just want to learn.

I don't know. I've not reused the same brass with multiple loads with 3N38, or any other powder, in 9mm, so I can't comment on that. (I have gazillions of 9mm brass.) 3N38 seems to be okay with compression, as noted in the link below when loaded for 9 Major.
https://www.ssusa.org/articles/2018/1/9/how-to-use-9-major-in-a-short-barrel/
And it can be very accurate pushing bullets fast in the right gun:
https://www.ssusa.org/articles/2020/4/28/accuracy-of-9-major-handloads/

People who question 3N38 in the 9mm have never used it in 9mm. It's a super powder. It's a little flashy and loud, but it delivers.

I have more experience with 3N38 in the 38 Super. It is super-fast and super-accurate.

 

[243winxb]

People who question 3N38 in the 9mm have never used it in 9mm. It's a super powder. It's a little flashy and loud, but it delivers.

Good to know, Ty.

The OP may want to get some pin gauges & measure primer pocket diameters? Before and after firing?

4 out of about 50) ranged in diameter from .1800" to .1820"

 

[243winxb]

Nine millimeter Luger ammunition loaded to Major power factor is called 9 Major―to distinguish it from regular 9mm Luger, 9mm +P and even off the shelf +P+, which might not make the power factor required for competition. A 165 power factor (bullet weight times velocity divided by 1,000) means that 115-grain bullets must go at least 1435 fps.

WOW, my plastic Taurus G3C might melt if i loaded that hot.

 

[reddog81]

Did you measure the primer pocket diameter before firing ?

I agree with this line of thinking. In order to know how much it "grew" you'd need to know the diameter of the primer pocket before firing. It could just be a larger primer pocket to start with.

 

[JimGnitecki]

Did you measure the primer pocket diameter before firing ?

No, I did not. .The primers before firing are 1475", as expected. But I have not yet measured the primer POCKETs.

Jim G

 

[JimGnitecki]

Link to the article?

http://www.natoreloading.com/9mmmajor/

Jim G

 

[Dale Alan]

I agree with this line of thinking. In order to know how much it "grew" you'd need to know the diameter of the primer pocket before firing. It could just be a larger primer pocket to start with.

Exactly my point , pin gauges don't lie . We all know some primers go in a little easier than others , or come out with less force . Many variables involved, but primer pocket diameter before firing is key with this test.

 

[JimGnitecki]

To be clear, VV does not show 3N38 for your bullet, or its sibling the 115 grain XTP. You're using data for the 115 grain Berry's HB RN TP.

Yes, as advised by Brad MIller PhD, who writes many of the the handloading articles for Shooting times Magazine, and who has run similar loadings (see his articles). Brad told me that since the HAP bullet is shorter than the Berry bullet, the pressures with the HAP bullet would be lower. He used QuickLOAD to do some simulations, as did I later. Although QuickLOAD is admittedly recognized as weak in its accuracy on handgun loads, when I did the simulations in both QuickLOAD and Gordon's Reloading Tool software, they both showed modest pressures at 8.0 grains, and did warn that the burn might be inefficient since only about 70% of the powder burns before the bullet exits the muzzle.

Jim G

 

[fxvr5]

WOW, my plastic Taurus G3C might melt if i loaded that hot.

Yeah, 9 Major is not for the timid, or all guns. Many competitors will load 115s a bit faster, near 1,500 fps, to ensure that they reliably make power factor.

 

[JimGnitecki]

SAAMI's velocities are 'nominal', aka typical. 3N38 is well known for producing very high speeds in 9mm and 38 Super within normal pressure limits. It's a favorite powder for IPSC/USPSA for this reason.

SAAMI's velocities are from a 4" barrel. The P210 has a 5" barrel.

I run 8.0 gr of 3N38 in 9mm from a 5" Kart barrel with 115 HAPs and get 1390 fps (at 1.100 OAL).

Wow, you are running a very short (1.100") COAL versus what VV recommends. And apparently successful. What prompted you to go that short?

Jim G

 

[JimGnitecki]

How do the primer pockets hold up? Getting more then 5 firings? Just want to learn.


The OP did pick the powder* , 8.7 grs that will produce the highest velocity, 1401 fps. .

I have only had 1 firing from most of the cases so far, with a few cases (40?) having ogtten their second firing. None with more than 2 firings so far, simply because I have not yet had time to get to the range and shoot. Out of the 600 brand new cases I bought, I still have some that have not yet been fired, but I switched to fired and resized cases specifically because that is what I intend to use long term. With 600 cases, it will be some time before any cases get 5 or more firings!

Jim G

 

[JimGnitecki]

How do the primer pockets hold up? Getting more then 5 firings? Just want to learn.


The OP did pick the powder* , 8.7 grs that will produce the highest velocity, 1401 fps. .

With only 1 or 2 firings on any of the cases so far, it is way too early to know.

Jim G

 

[JimGnitecki]

Good to know, Ty.

The OP may want to get some pin gauges & measure primer pocket diameters? Before and after firing?

Good idea. I had not yet gotten that far. Just found the article on primer grwoth last evening.

Jim G