Enlarged Primer Pockets

[Merc]

I've been reloading for a couple years and finally ran across something for the first time while at the range the other day. I had a primer pop out of a spent case when I ejected it from my M1917. I brought that case plus the other cases home to reload and found that the primer pocket on the case with the popped primer was enlarged to the point where it would not hold a fresh primer. I measured the enlarged pocket with my digital calipers and found that it measured .210" wide. I measured the width of the pockets on three dummy rounds I have with newer cases. Two measured .206" and one measured .207". The new large rifle primer measured .209". All of my cases are made by PPU and most have been fired multiple times. I'm curious to know what would cause the primer pocket to expand by .004", especially since it's in the thickest part of the case. I'll have to start checking the pocket hole size on the next group of cases that I reload. Here, I thought I'd be able to reload these cases indefinitely if I only neck size and anneal necks every time, guess not.

[Sunray]

"...what would cause the primer pocket to expand..." Somebody lit a fire in the case that created 50,000 plus PSI pressures to build up. Said pressures go in every direction and cause all parts of the case to expand. The only part that doesn't get resizing is the primer pocket.
.210" is the max diameter for a Large Rifle primer pocket. The primer itself can be no larger than .213".
Oddly enough the minimum diameter for an LR primer is .2105".
"...start checking the pocket hole..." Maybe on those Prvi cases, but not as a normal thing.

[bruce]

Once upon a time I was doing a lot of shooting with a Rem. 700 SF-VS in .308 Winchester. I used Remington brass w/o problems. Excellent results. Then I bought some Federal Gold Medal Match .308 brass. Believe it or not, the primer pockets were enlarged usually after no more than two reloads. Winchester brass did not demonstrate this problem. I dumped the Fed. GM brass and spent the next 15 years shooting that rifle w/ Rem. and Win. brass. Never had another brass problem. Given that the 1917 is chambered in .30-06, you should get your hands on some USGI Lake City brass, or get some good quality commercial brass such as Winchester or Remington. Properly prepared and used, such cases will give you many many multiple reloads.

Neck sizing with a bolt-action is a good way to get best results with brass. You will occasionally have to full-length resize, but when you do make sure to only bump the shoulder back a smidgen... just enough to allow easy chambering. You should not have to anneal case necks every time you reload the brass but rather wait till the necks are beginning to get work hardened from resizing. HTH. Sincerely. bruce.

[bigedp51]

The Lake City 5.56 case vs some .223 cases is a good example of what happened to your brass. Some brands of brass are said to be softer but that is not the whole story.

The flash hole web thickness adds radial strength to the base of the case meaning how soon the primer pockets stretch out of shape.

I have factory loaded Federal .223 cases that had over sized primer pockets after the first firing and the photo below shows why.





The link below is good example, it doesn't actually measure pressure it measures the strength in the base of the case. Meaning how much pressure a given brand of brass can take.

Simple Trick for Monitoring Pressure of Your Rifle Reloads

http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads

Below are Rockwell tests of brass hardness in the base of the case with Lake City cases being the hardest.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests

http://bulletin.accurateshooter.com/2014/05/how-hard-is-your-brass-5-56-and-223-rem-base-hardness-tests/

Before doing anything to a fired case I check the primer pocket with pin gauges that are .0005 smaller than the primer I'm using. The reason for this is I prepped 500 once fired Federal .223 cases, sized, uniformed the primer pockets, uniformed the flash holes etc. Only to find out when priming these cases that 1/3 of them had over sized primer pockets.

So now I use the pin gauges "FIRST" and not waste any time prepping cases before this check, and during primer seating if any primer feels loose during seating it is checked with a Lee depriming tool.

If the primer moves with just finger pressure the case goes in the scrap brass bucket.



The main reason for these tests is "dad" reloads for his sons AR15 rifle and his own two AR15 rifles and "dad" isn't going to be blamed for what happened below. The person who posted the photo below in a AR15 reloading forum said he didn't worry about loose primer pockets and would just replace the bolt when it got bad enough.

And Forest Gump said "stupid is as stupid does", and brass is a expendable item and the bolt face is not.

[Merc]

Thanks to all for sharing your wealth of knowledge.

I probably got 10 or more reloads with the PPU cases with only one enlarged pocket so I don't feel they owe me anything. I'll refine my inspection technique to include giving the new primer a push with the de-priming tool. Or, I could measure each pocket width with my digital calipers which easily shows the degree of enlargement. So, what's the recommended brand? Lake City has the hardest brass and should hold up the longest? PMC and Winchester have thicker heads but may not be as hard?

[p246]

Bigedp51 nice post with good illustrations.

Merc I just check the brass I get. If you get 10 reloads out of it you are in the game. Like I said I use the heck out of PPU in 303, In the tight bores I get plenty of reloads. In the brass eaters it does not matter. I also have better luck with getting a good reading on size with pin gauges then calipers, but sometimes you got to use what you have and I understand.

[musketshooter]

The cause is an enlarged flash hole which allows to much gas pressure on the primer which in turn stretches the pocket,

[Merc]

The cause is an enlarged flash hole which allows to much gas pressure on the primer which in turn stretches the pocket,

That makes sense. So, it's a gradual process and how quickly it occurs depends on brass thickness and hardness, but it's going to happen at some point in time to all cases regardless how gently we handle and load them.

[Merc]

Bigedp51 nice post with good illustrations.

Merc I just check the brass I get. If you get 10 reloads out of it you are in the game. Like I said I use the heck out of PPU in 303, In the tight bores I get plenty of reloads. In the brass eaters it does not matter. I also have better luck with getting a good reading on size with pin gauges then calipers, but sometimes you got to use what you have and I understand.

The PPU .303 brass has held up really well through 10 or more reloads without head separation or overly enlarged primer pockets. It has a slightly smaller powder charge than the .30-06 which probably helps. By only neck-sizing the cases, I noticed the walls of the cases have expanded to fit the generous No. 4 Mk 1* chamber to the point where they've become difficult to chamber and eject. Have you noticed this? I've not seen this happen with the .30-06 cartridges.

[S.A. Boggs]

Are you using the appropriate head space gauge to set your sizing dies?
Sam

[p246]

The PPU .303 brass has held up really well through 10 or more reloads without head separation or overly enlarged primer pockets. It has a slightly smaller powder charge than the .30-06 which probably helps. By only neck-sizing the cases, I noticed the walls of the cases have expanded to fit the generous No. 4 Mk 1* chamber to the point where they've become difficult to chamber and eject. Have you noticed this? I've not seen this happen with the .30-06 cartridges.

If you neck size the body will expand to the point it needs full length resized every so often. I full length everything in 303 and 30-06 because I want to be able to shoot it out of all my L.Es and American Mil Surps, so no direct advise. On others I have singles (example 1918 Carl Gustav 6.5 X 55) I full length resize every fourth firing. Others might be able to tell you what they are doing in 303 and 30-06. A chamber gauge could be used but in military 303 bores I've been told it's hit or miss due to bore size differences. Good luck.

[Merc]

If you neck size the body will expand to the point it needs full length resized every so often. I full length everything in 303 and 30-06 because I want to be able to shoot it out of all my L.Es and American Mil Surps, so no direct advise. On others I have singles (example 1918 Carl Gustav 6.5 X 55) I full length resize every fourth firing. Others might be able to tell you what they are doing in 303 and 30-06. A chamber gauge could be used but in military 303 bores I've been told it's hit or miss due to bore size differences. Good luck.

I've been thinking that I'd eventually have to full length size the 303 cases. Forcing the expanded cartridges into the chamber is probably a great way to wear out the locking lugs. Do you occasionally experience case head separation in either caliber?

[bigedp51]

The cause is an enlarged flash hole which allows to much gas pressure on the primer which in turn stretches the pocket,

The same amount of pressure will go through the small hole as a large hole, meaning the size of the hole doesn't change the amount of chamber pressure. All the hole size changes is "flow or volume" just like the nozzle on your garden hose.

Over sized primer pockets/base expansion is caused when the chamber pressure exceeds the strength of the case. Meaning brass hardness and case design and a thicker flash hole web adds radial strength to the base of the case. And if you notice below the flash hole web is "below" the supported part of the case and the case starts to expand "above" the flash hole web.



The link below does not tell you chamber pressure, it tells you the strength of your brass and loading limits. Meaning how much pressure the brass can take before it reaches its elastic limits and can not spring back to its original shape.

Simple Trick for Monitoring Pressure of Your Rifle Reloads

http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads

[Merc]

Big Ed,

Thanks for the info. The stiff extraction I'm experiencing from the expanded 303 cases which, according to the link, is one of the signs of high pressure. As previously mentioned, I'm using starting loads BUT neck size only. These expanded 303 cases have been fired and reloaded multiple times which has probably caused or allowed progressive body expansion to reach its current size. Would you agree that a better test might be to evaluate a new or full length sized case for symptoms of stress, i.e. expansion, extraction stiffness, etc. after it's been fired only once?

[PhillipM]

Are you using the appropriate head space gauge to set your sizing dies?
Sam

How do you use a headspace gauge for that?

I have an RCBS case mic which while checking fired brass, my chambers are all on the minimum end of the scale.

p.s.

I hope your health is improving.