What exactly is happening that causes primer pockets to get loose? Also why so inconsistent? Seems like such a small amount of mine suffer. But mainly just looking for a detailed explanation of what is happening that causes this. Your rounds are to hot is not the answer either. Thanks for any insight.
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What’s the science behind loose primer pockets?
- Thread starter Simonsza1
- Start date
How many firings
What brand of brass
What brand of primer
Caliber and specific load
What brand of brass
What brand of primer
Caliber and specific load
The pocket becomes bigger than the primer….
On a serious note. It’s generally that the primer pocket and cartridge get expand beyond the elastic limit of the brasses ability to return to its original size.
This causes it to stretch and the primer pocket becomes larger. Could happen over several firings or in one firing.
But at a metallurgical, level the brass expands under pressure and doesn’t return all the way back to its original size. This happens when it goes beyond the elastic limit which is the point at which it can’t go back to its original size. Don’t think of metal as hard, but think of it as taffy which can be stretched and pulled and reshaped. Just takes a little more force.
Hope that helps.
On a serious note. It’s generally that the primer pocket and cartridge get expand beyond the elastic limit of the brasses ability to return to its original size.
This causes it to stretch and the primer pocket becomes larger. Could happen over several firings or in one firing.
But at a metallurgical, level the brass expands under pressure and doesn’t return all the way back to its original size. This happens when it goes beyond the elastic limit which is the point at which it can’t go back to its original size. Don’t think of metal as hard, but think of it as taffy which can be stretched and pulled and reshaped. Just takes a little more force.
Hope that helps.
Not asking about certain brass. Asking what it is in firing that is actually causing this event to happen and how it happens.
Short answer is pressure that exceeds the elastic limits of of the brass. Different brands of brass vary in case head strength. Other cause is simply wearing out from seating repeated priming.
Again not asking about a certain brass brand, caliber, bolt or gas just asking how exactly it happens. I know it’s pressure over fairings just wondering how it impacts the actual pocket and how it really gets it stretched out. Thanks.
Primers are very powerful, so the pressure in the primer/pocket gets a head start before chamber pressure peaks. Chamber pressure then adds to that via the flash hole.
I think your question has been answered, at least three times. Oh, and yeah, hot loads will do it too.......
So, brass isn’t the only thing that expands when you pull the trigger. Among other things, the chamber/barrel wall itself expands.
So, the chamber expands slightly, the brass expands to fill that slight larger chamber. The steel barrel then springs back and so does the brass.
Brass has a much lower yield rate than steel. Which is why sizing is needed. The chamber will spring back the entire life of the barrel. The brass will continually need sizing.
On larger things like .338 rounds, this is why many times a larger tenon thickness is needed. A thinner wall will expand too much, allowing the brass to expand too much. Creating stuck/sticky cases no matter what. As the brass wasn’t able to spring back enough.
What does that have to do with primer pockets?
Well, we don’t resize those. This is the reason the case head an such is kept hard and shouldn’t been annealed. So that it will retain its size as long as possible.
Eventually, depending on many things, the area around the primer pocket will expand enough it will have loose or falling primers.
Many things dictate the speed in which that occurs. But it will eventually occur. Obviously hotter rounds and such will happen faster.
That’s a brief overview on what causes it.
Not saying you’re wrong, but my guess is this chamber expansion is too small to even be measured. Sort of like saying water is compressible. Yes, but very slightly, and not significantly enough to matter…so essentially not.
Depends on pressure and the thickness of the chamber wall. Also the metallurgy.
Measurable is relative. To how good your measuring equipment is. Not going to measure it with a micrometer. But in lab level testing, it is very measurable and recordable. If you ever go to Springfield armory, they have some of the old test gear on display.
The barrels will also react under firing, and “move” not just in a harmonic, but think of it like an ostrich swallowing a grapefruit. A tiny bulge will follow the bullet down the length of the barrel. It’s one of the reasons you don’t want to clamp things on a barrel. And why thicker Bull barrels developed for high pressure and high velocity cartridges. At extreme levels of bulge and/ or obstruction, barrels burst. But if they don’t reach the fracture point but do exceed the elastic limit, you get a bulged barrel.
There is a lot of science to internal ballistics. Some good books on it if you want to geek out! Mostly formulas I need a physicist to explain.
Cheers, Sirhr
If it didn’t, the brass wouldn’t need to be resized on the body. As it wouldn’t be able to stretch anywhere except to get longer.
Also, this is a big time problem with .338 and larger and why many actions use a larger tenon.
This stuff isn’t “guessing.” It’s well documented.
You don’t get 60k + psi and the steel doesn’t move.
This is also why some pressure testing equipment use sensors glue to the outside of the barrel at the chamber.
Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace
Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.
www.shootingsoftware.com
Hope your not referring to the op (me) who asked the question. I never said any of these replies are wrong. Not reading all the replies and paying attention to who said what before putting up a post stating the wrong thing is more along the lines of classic SH.
Touché, was in reference to Fig's post...Hope your not referring to the op (me) who asked the question. I never said any of these replies are wrong. Not reading all the replies and paying attention to who said what before putting up a post stating the wrong thing is more along the lines of classic SH.
So you're saying that stuck cases are based on how much the steel expands, and not on the brass? If you neck size only you get stuck cases where the chamber doesn't "change" even if it is expanding and contracting on each shot. I don't dispute that the steel moves, I just question that this is the causality or the primary causality. Seems more likely that it's the brass being worked and re-stuffing a primer in the pocket twenty times...
If the steel doesn't move, or moves only an "insignificant amount," there is nowhere for the brass to go- unless your contention is that brass is stronger than steel and can push it out of the way. However, if the steel moves a significant amount (most people don't actually know what "significant" means), it creates extra space for the brass to expand into. When the tempered steel barrel shrinks back down, it clamps down hard onto the brass that expanded into the extra space.
^^^
The higher the pressure the more the brass expands. Brass only springs back so much. Steel springs back a lot more. If you run pressure high enough you will stick a case by virtue of the steel clamping down on the brass like Mr. Hlee explained.
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The outside diameters of the case, in its unfired state, are smaller than the inside diameters of the chamber. The case expands to fill that gap and doesn't spring back 100%. That's why it has to be resized.
The chamber begins expanding once the brass has fully expanded to eliminate the radial gap. Once pressure subsides, both the chamber and brass contract back again. Like I said brass doesn't spring back 100% but it does enough to be easily pulled out of the chamber by hand.
For arguments sake assume cartridge brass springs back about .001” cuz that’s what I have seen.
Steel springs back to zero in firearm applications. If you run pressure high enough to expand the chamber by more than .001” the case will get stuck.
Brass cases are designed to yield which is why the do not return to the original unfired dimension. The case expands to the chamber wall then both expand based on the stress strain relationship of the chamber wall. When the pressure decreases, the chamber and the brass case return along the stress strain curve. The chamber to original because it was stresed below the yield point. The brass to an interim dimension because the stress was beyond the yield point. If the case expanded too much, the chamber contracts more than the case and hard bolt lifts occur.
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More powder, more powder in a load work up.. until short brass life.. back off 6% normal powder or 3% for temperature insensitive powder.
I have been doing this for a long time with a lot of guns.
I have been doing this for a long time with a lot of guns.
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Too much guessing without any knowing. Your guess is 100% wrong.
Have you ever heard of a strain gauge? It's literally a sensor that measures expansion of the steel (or whatever other surface it's applied to). A strain gauge on the outside of the barrel over the chamber gives a direct measurement of how much the steel barrel expands, and it's far from "too small to be measured". Those measurements can be then correlated to pressure based on dimensions and material properties of the steel.
god hates you .your primer pocket hole is now too large , and you need to close it up or get new brass
you can fight back
you can fight back
I’m not saying that’s the only reason cases get stuck.
I’m not saying it’s the only reason primer pockets expand.
But, I am saying that chambers absolutely expand and if they expand too much, you will have issues.
And the issue may not be a stuck case. It could be you get 10 loading cycles instead of 20 because the tenon is too thin or the steel expands more than another barrel.
Regardless, the chamber always expands. But it will spring back longer than the life of the throat.
Brass will not spring back as well and needs to continually be replaced.
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In a proper system yes.
If the chamber expands too much, you have extraction issues.
Hence things like larger tenons and Litz preferring virgin brass.
As well as if you don’t size then body down, you’ll eventually have feeding and extraction issues.
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Well, there is another reason. Pocket cleaning. I have reduced this error by hand de-priming and then Ultrasound which cleans the pockets good enough, with tumbling to remove lube after sized. Number of pocket rejects has dropped significantly with the same batch of primers.
My experience is this…brand XX brass designed for sammi pressures fails (primer pockets) in X number of firings. ADG, Lapua, etc. extends brass life to extreme extents using the exact load. We all know the pressures are higher because the water capacity is lower. However, the life of the better man brass remains considerably higher even when the pressures increase considerably vis-a-vis more powder.
Metallurgy must be the answer relative to the brass case. The tenon won’t expand until force is applied, the force is the expansion of the brass case, therefore the remedy is better brass or lighter loads.
Metallurgy must be the answer relative to the brass case. The tenon won’t expand until force is applied, the force is the expansion of the brass case, therefore the remedy is better brass or lighter loads.
I think the question was, why do pockets fail at all. Not why in more or less firings.
The answer isn’t a one off thing. It’s a combination of things. No one is saying the tenon expanding is the only reason anything happens.
Just that the chamber does expand and allows the brass to expand outwards. The pressure doesn’t stop against the brass wall when the chamber expands, it keeps going.
Better brass (better can be better for man reasons) will obviously last longer than lesser brass.
But, you can take the same Lapua brass and put it in a chamber that expands more than another chamber and that Lapua brass will last less firings than the other Lapua in the other chamber.
Better brass is better brass, but other factors are at play that dictate the life of that brass. Including pressure from hot or not hot loads.
Web thickness has a part in this. Some years back there was warning about webs in .223 Federal brass being too thin (web thickness)
to safely reload. The web is like a disk at the end of the case with a hole in it (flash hole).
With a thin web the case internal volume also is closer to the end of the chamber and is not fully supported.
If the base expands because the chamber expanded it will leave a contact/rub ring on the outside.
0.002" diameter growth can allow the web to stretch and open the primer pocket.
Work hardened case bodies should actually be stronger than virgin.
It's web stretch, resizing, web stretch, sizing that leaves pockets oversize.
Extra headspace can also allow the body to stretch and stretch the web.
Web stretch open pockets.
Measure web thickness of your various brands.
Here are two cases for the same chamber. A 6mm HAGAR (left) resized to 22 NOSGAR and a 22 Nosler brand (right) case.
When cleaning pockets only the edge of the pocket at the bottom (where the primer seats) and the flash hole needs to be cleared. Try not to scrape the sides of the pocket. I use a sharp pick and ring the pocket.
to safely reload. The web is like a disk at the end of the case with a hole in it (flash hole).
With a thin web the case internal volume also is closer to the end of the chamber and is not fully supported.
If the base expands because the chamber expanded it will leave a contact/rub ring on the outside.
0.002" diameter growth can allow the web to stretch and open the primer pocket.
Work hardened case bodies should actually be stronger than virgin.
It's web stretch, resizing, web stretch, sizing that leaves pockets oversize.
Extra headspace can also allow the body to stretch and stretch the web.
Web stretch open pockets.
Measure web thickness of your various brands.
Here are two cases for the same chamber. A 6mm HAGAR (left) resized to 22 NOSGAR and a 22 Nosler brand (right) case.
When cleaning pockets only the edge of the pocket at the bottom (where the primer seats) and the flash hole needs to be cleared. Try not to scrape the sides of the pocket. I use a sharp pick and ring the pocket.
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I haven’t cleaned a primer pocket in years. Never seemed to make a difference. The powered primer pocket cleaners always have looked like reamers to me.
Resizing has nothing to do with primer pocket loosening. Pockets can loosen just as fast when neck sizing only as when full length sizing (which doesn't affect the web anyway. That also doesn't correlate with the fact that a hot load can loosen a primer pocket in a single firing, with no sizing happening at all.
Few things to add.
Firing brass doesn’t work harden it that much. It’s counterintuitive. However AMP had been testing this stuff for years and they have seen very little hardening of brass due to firing. Especially when compared to sizing.
Also, rings around web/case head typically form when there is excessive headspace and the brass is stretched length wise. Typically not from the chamber expanding. The ring forms where the thinner case body meets the thin web. You and I may be talking about different “rings” though as there’s several types.
You can take rifles in the .338 and larger that always have trouble extraction because the chamber expands too much, and you won’t see much of a ring, if any at all.
If you are not loading hot, have the proper barrel wall outside of the chamber, are bumping the shoulders back minimally, and have a proper sizing die that minimally sizes the body, you’ll still eventually have loose pockets. For all the reasons we have all described.
some primers are bigger and some primers are smaller, so first one go harder into primer pocket.
some primers are inconsistent, like mine from magtech, and some get normaly into primer pocket and some get loose; the same box and lot.
some primers are inconsistent, like mine from magtech, and some get normaly into primer pocket and some get loose; the same box and lot.
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