Loose Primer Pockets

[Robinhood]

Loose primer pockets. Often people say that over pressure loosens primer pockets. While that may be true, more often the culprit is an oversized chamber combined with high pressure loads. If a reamer is out of spec or the tailstock center-line is off just a few thousands of an ", it can cause the base of the chamber to be cut OS. Over polishing could be the culprit also.

In this drawing you can't match up exact numbers but you will see the case major diameter at the base is .4703". This is about .070" in from the breach face when chambered. At .200" into the chamber the .4714. A difference of about .0011" on diameter. calculating the distance and taper of the 308 case that .070" equals to about .0008 on diameter. Therefore your SAAMI spec'ed chamber should give you less than .002" between the chamber and the base of the case. In a perfect world...........Just something to think about.


http://reducerecoil.com/wp-content/uploads/2015/01/308-Winchester-specs.jpg

[bigedp51]

On the vast majority of rifle cartridges the very base of the case is not supported with the exception of rimmed cases. Meaning a over sized chamber would cause a bulge where the case does contact the chamber. "BUT" high pressure will have a effect on primer pocket life.


https://i.imgur.com/IBJQA9p.gif

One of the biggest problems of short primer pocket life is the thickness of the flash hole web and the hardness of the brass. Below you can see why Federal get a bad rap for oversized primer pockets after a few reloadings

. https://i.imgur.com/cYeTsDp.jpg

Below Lake City and contract ammunition for the military uses harder brass and thicker flash hole webs.

https://i.imgur.com/4kXrGuI.png

https://i.imgur.com/ohI86Bf.jpg

At the link below measuring the expansion just above the extractor groove doesn't tell you the chamber pressure. It just tells you how soft the brass is and the strength of the flash hole web. Meaning the same load in a Federal case would show more base expansion than a Lake City case.

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

[Robinhood]

He ed! Good to hear from you. Neat graphics that skew the correct information. If you look at your first graphic you will see your argument is counter intuitive. The primer pocket depth is within .010" of the cartridge protrusion. You then have approximately .065 above the primer for the flashhole. So the graphic is not only misleading, it is incorrect.

Draw the breach face in a straight line at .010 above the bottom of the primer pocket rather than showing .300" protrusion and you will get the real story.The bulge cannot take place there because it is captured by the chamber....unless the chamber is ...oversized. I had read all of that information before from the same place you got it. It did not stand the test then and it does not now. Sometime pictures explain things and sometimes they tell lies. :p

Your graphic tells the tale of incorrect protrusion. Nothing else.

[Robinhood]

For your comparrisonhttps://external-content.duckduckgo.com/iu/?u=http%3A%2F%2Fuploads.tapatalk-cdn.com%2F20160421%2Fb902120933b29cb379e768768969d 8ee.jpg&f=1&nofb=1

[bigedp51]

Sometime pictures explain things and sometimes they tell lies. :p

Your graphic tells the tale of incorrect protrusion. Nothing else.

Darn, I looked on the internet for hours trying to prove you wrong and couldn't find anything. :frusty:

But I still decided to not invite you to my birthday party this year anyway. :smile-new:

Protrusion aside I'm only half wrong, below is a photo from AR15.com and the reloading moderator. A two inch rod was used to measure the flash hole web thickness. The base of the rod was drilled and cup shaped so any protruding burs would not give a false reading. Any Federal or other cases with a thin flash hole web were tossed in the scrap brass bucket as not worth reloading. I had factory loaded 09 and 10 dated Federal cases with loose primer pockets after the first firing. The two inch rod saved you from sizing and prepping the cases only to find loose primer pockets when seating the primers.

I made up my own two inch rod to check my Federal cases but then I said why bother inspecting all theses cases and just started using nothing but Lake City brass. That being said it is how hard the brass is in the base and the thickness of the flash hole web that governs primer pocket life.

https://i.imgur.com/POsazjb.jpglongevity

Below both these .303 British cases were fired in my 1943 No.4 Enfield rifle with a large diameter chamber. The Prvi case is larger in diameter and .010 thicker in the base than the HXP case. And my point here is the case construction has a great deal to do with primer pocket and case longevity even with large diameter military chambers.

https://i.imgur.com/eM3H3ls.jpg

During the 1968 Congressional hearings on the M16 rifle jamming problems, it was found the brass used was too soft and the case hardness was increased.

https://i.imgur.com/suc7fK5.jpg

https://i.imgur.com/OujD1z7.jpg

https://i.imgur.com/JcVlKzc.jpg

[Robinhood]

Let me quote myself....


Loose primer pockets. Often people say that over pressure loosens primer pockets. While that may be true, more often the culprit is an oversized chamber combined with high pressure loads. If a reamer is out of spec or the tailstock center-line is off just a few thousands of an ", it can cause the base of the chamber to be cut OS. Over polishing could be the culprit also.

[bigedp51]

Let me quote myself....

I collected milsurp rifles that had large military chambers and if you wanted longer case life you used harder and better quality brass. With commercial rifles and cases you still have plus and minus tolerances for the chamber and case diameter. Bottom line the brass case has elastic limits and this varies between brands of ammo. And if you apply too much pressure to that brand case the brass will not spring back.

I understand what you are saying, if you have a fat chamber and skinny brass the case can expand in diameter more. But the quality of the case and its construction also plays a big part in case life.

https://i.imgur.com/4kXrGuI.png

[Robinhood]

Agreed.

[charlie b]

Interesting stuff.

I ran into the primer pocket problem with my Axis in .223. 4 loadings and most cases were toast. Some made it to 5. Even the lake city brass I had only got to 5 reloads before the primers fell out. This was with less than Sierra max loads (which are lower than Hogdon). Based on CFjunkie's posts I went to Lapua and they have gone 7 so far and still good (he gets more than 10 reloads).

Interesting that my .308 has had no problems going over 10 reloads with Winchester and Hornady brass. Both are now used for cast loads so they might never wear out. Still have not had a case neck split either. Maybe Savage uses 'fresh' reamers for the model 12's (mine is a BVSS) so the chamber is tighter?

[Robinhood]

Just for giggles and grins, What 223 brass was blowing the primer pocket out.

[charlie b]

LC, FC, Winchester and Hornady.

[Robinhood]

If you ever have that barrel off the action someday, measure the breach end of the chamber.

[Texas10]

After reading that graphic for the first time showing FC brass with a web at the flash hole as measuring .048 I sectioned several of my FC .223 brass harvested from American Eagle ammo and measured the web. It was .070 at the flash hole, so in all probability the brass used in the graphic was not made at the same time or by the same manufacturer as the FC brass I have.

Over the past 5 or 6 years I have found that some brass from American Eagle 223 loads is particularly low quality, and was tossed instead of saving for reloading. Some had flash holes that were as much as 1/2 diameter off center, and without digging that brass out of my scrap pile, I'd bet those had the thinner webs described above.

Doing the same for some Winchester 223 brass, I found nearly identical thickness (.070) , and total weight was also nearly identical to FC brass. To me, that's a clear indication both were manufactured at the same facility at about the same time, probably at the Lake City plant as some of the American Eagle brass I have seen is stamped LC.

It is also a popularly held belief that Federal brass (FC) is soft and not ideal for hand loads. In my experience that is simply not true of all FC brass. For instance Federal Gold Medal Match 308 brass is indeed soft by design, and won't stand up to repeated loadings. However FC 223 brass is quite hard and sill stand up to dozens of loadings including at or near max pressures.

Bottom line is that few name brand ammo manufacturers actually make their own brass, preferring to contract out that job to the lowest bidder, so year to year, even contract to contract there can be significant differences in quality.

Furthermore, the particular American Eagle 50g Tipped Varmint ammo in 223 that I purchased was apparently a limited run under contract by Federal and was never featured on their website. It was extremely accurate frequently placing 3 and sometimes 4 of 5 into one hole at 100 yds. Information on this load was hard to find and only obtained by me after calling Federal C.S. who then emailed me a copy of the technical data. Sadly, it has since been discontinued.

I still have some of this ammo, bought years ago, and use it as a benchmark load if I'm suspecting something other than a load is causing poor groupings. There are some interesting aspects to this load, for one being a tar like substance was used in the case neck area that may have contributed to its extreme accuracy. I found that moving the bullet out slightly with an inertial puller and then reseating it would destroy the inherent accuracy of the ammo. Interestingly, the factory data sheet indicated it was NOT a sealed round, so the use of tar may have more to do with making the round accurate and consistent, rather than weather proof.

[charlie b]

If you ever have that barrel off the action someday, measure the breach end of the chamber.

I will...but, it only has 2500 rounds through it so far :) Maybe in another year or two :) Wish I still had my small bore measuring tools and I could do it today.

[hardnosestreetcop]

On the vast majority of rifle cartridges the very base of the case is not supported with the exception of rimmed cases. Meaning a over sized chamber would cause a bulge where the case does contact the chamber. "BUT" high pressure will have a effect on primer pocket life.


https://i.imgur.com/IBJQA9p.gif

One of the biggest problems of short primer pocket life is the thickness of the flash hole web and the hardness of the brass. Below you can see why Federal get a bad rap for oversized primer pockets after a few reloadings

. https://i.imgur.com/cYeTsDp.jpg

Below Lake City and contract ammunition for the military uses harder brass and thicker flash hole webs.

https://i.imgur.com/4kXrGuI.png

https://i.imgur.com/ohI86Bf.jpg

At the link below measuring the expansion just above the extractor groove doesn't tell you the chamber pressure. It just tells you how soft the brass is and the strength of the flash hole web. Meaning the same load in a Federal case would show more base expansion than a Lake City case.

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
Ive got a Boat load of the PMC .308 Brass, it’s definitely heavier than my Winchester commercial 308 brass. Thank Ed

[darkker]

Ive got a Boat load of the PMC .308 Brass, it’s definitely heavier than my Winchester commercial 308 brass.

Cases weigh different amounts for several different reasons:
Balloon head Vs flat head, alloy difference, standard lot variance, primer size, etc. When Frankfort and Pic were testing 5.56 in the 70's over the dropped primer issue, they found a stunning variance in case weight even from the same production line; whereas the actual volume difference and corresponding pressure differences were negligible. I also pressure tested this fact out a couple years ago when testing LR Vs SP Creedmoor brass. Despite marketeering wank by Lapua, they had a significantly larger case variation in weight than the Norma. Regardless, loading identical charges by volume on both cases, produced the same pressures.

Texas,
It is true that Federal heat treats differently than "most", especially towards the case head. The faster the case obturates, the potentially more accurate the ammo. Couple that with a larger chamber and you can have issues. I've had cases that grew significantly in the extraction groove, blew primers out and was general unpleasant, running PT confirmed @45,000 psi loads.

If you want to know volume and how your burning curve will be impacted, measure volume. If you simply want to know how much winter weight you've gained, weigh the cases.

Cheers

[Robinhood]

Thanks for the good input Tex and Dark.