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1st safety post,..casehead seperation (new guys)
JustC
Member Posts: 16,056 ✭✭✭
Ok guys,..take a look at the first case from the left. if the picture was better you would see the case is slightly expanded a little ways above the rim. This straight walled case was fired and loaded repeatedly in an obviously sloppy cylinder. You can find out how loose your chamber is by running your thumbnail (under fair amount of pressure) from neck to rim direction. If you feel or can quite often see where the case gets a few .001"s larger in diameter from this point just above the rim for the remainder of the body towards the neck,..that is an indication of a slightly large chamber. This is very common in factory rifles.
Now,..take a look at the second case from the left. You can see the small crack forming around the circumference of the body. This is the area where internaly, the casehead material is no longer solid, as it joins the powder cavity. After repeated firings in that oversized cylinder and repeated FL sizings, the brass has stretched to the point of being too thin to even hold itself together. Had you missed this and loaded/fired this case again, you would have been sorry.
Now,.on to bottlenecked cases. Look at the two rifle cases (6.5x55). The left side case shows the tell-tale (shiny ring) that appears just before a case-head seperation. That shiny area is actually the brass being thinner than anywhere on the rest of the case. Just for a experiment,..take a peice of gum in say a pink bubble gum color. Take the gum and stretch it between your two hands,...see the color in the middle getting lighter and lighter as the gum gets thinner and thinner? That is the same thing.
Now,.the right side case shows a seperation crack that somehow did not let go when it was fired last. if you missed this and loaded/fired this case again,..you would REALLY have been sorry.
As a NOTE: do not confuse this bright ring with the brighter spot/ring left around the case body down near the rim,..this one is where the die body stops making contact with the case body. This one will be there from the first sizing and on for the rest of it's life. Check a 1x, 2x, etc fired and sized case that you know is nowhere near being loaded too many times. You will see the shiny area I mean,..this is normal. Now,..the seperation will occur just above that area a few 1/10's of an inch depending on the thickness/height of the internal casehead/primer flash hole area. This bright shiny ring is something you will need to be on the lookout for the more times you reload your brass. KEEP TRACK OF HOW MANY FIRINGS YOU HVE ON EACH LOT OF BRASS. This will give you a good idea of when to start looking on other brass in other rifles you have.
Hope this helps.
why chase the game when the bullet can get em from here?....
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Does anyone have a stress strain curve for brass? With that you could actually calculate, by how much you have trimmed off, when the brass will get to thin, reach is elasticty point, and then when it would break.
By knowing what the length was when you started, to how much you have cut off, you would be able to calculate with in certain persision, how much you could trim off of each case before it had to be thrown away.
What does happen when the cases seperate in the chamber?
To add a lil on the subject of watching pressure signs.
Casehead seperation is probably at the extreme level of over pressure.
Other signs to watch out for is:
Heavy Bolt lift: After firing a round and the bolt is REALLY heavy to lift and extract the round. Thats a good indication of pressure.
Flatten primers: Primer is completely FLAT after firing, there are no round edges.
Primer Crater: if your primers start to flow into the firing pin hole and you start to develop a lil bur on your primer.
And if you have a chronograph, check your velocity. If everyone is pushing 2700 FPS with a 308 Win shooting 175gn bullets and you start pushing 2850 2900 with the same setup, maybe need to back off the powder a lil.
And just start SLOW. Just because a book says it is ok to use 46gn of Varget, don't start there. Start low and work your way up.
One last thing I can think of. GAS guns/Semi autos do not handle the same pressures a BOLT gun will.
HTH,
Vu
Sticky bolt lift,..is a sign that you are Wayyy tooooo high in pressure. That in my experience is usually the last pressure sign after ejector marks and then primer cratering, followed by primer flattening (usually appears that the primer has filled the entire primer pocket from edge to edge) without that slight gap around the sides of the primer as ContacFront has stated.
This is one of the situations you will need to try your best to avoid. The gassess escaping the seperated case will find their way to your face and eyes around the bolt raceway (unless it is one of the mauser designs) and out the magazine well and trigger notch in the stock, and end up at your fingers and hand. Either area will suffer at least slight burns and often brass fragments will require the help of a doctor to remove them from your person.
PAY ATTENTION
why chase the game when the bullet can get em from here?....
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The one area where I respectfully take issue with some of this commentary is the use of "flattened" primers as a sign of pressure issues. Perhaps it is just me, but IME, most primers flatten under even mild loads. When I look at a primer for warnings of excessive pressure, I'm looking to see if the area around the firing pin has flowed backward ("cratered"). In the absence of this situation or other symptoms of problems, I don't lose any sleep over the face of primer being flat.
"There is nothing lower than the human race - except the french." (Mark Twain)
I believe that flat primers are one of the first indicators of pressure signs followed by a primer that has flowed into the firing pin hole. Most of my loads cause a primer to flaten a lil but not to the point where there are no round edges at all.
why chase the game when the bullet can get em from here?....
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Don't want to step on your toes, but please don't tell people to "start low" with loads! You CAN have an explosion by using TOO LITTLE POWDER!! I'm sure you know this, but didn't phrase it correctly!
Best to say "Start at the MINIMUM recommended loads"
Merc
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All American Arms Company
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START WITH MINIMUM RECOMMENDED LOADS AND WORK YOUR WAY UP. [:D]
This mainly will happen with very fast pistol powders in rifle cases when someone is experimenting with using blue dot or some other extremely fast powder. If they were to fill the case even 1/2 way with that powder,..they would blow the rifle up then as well. This is not a good thing to practice. Stick to appropriate burn rates and experiment with SLOW powders if you wish,..experimenting with fast powders needs to be undertaken with a lot of experience in burn rates and extreme caution still need be applied.
why chase the game when the bullet can get em from here?....
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Free Men do not ask permission to bear arms.
Some reloaders use the thumb rule of "trash when they need trimming for the 5th time".
As Justen pointed out, excessive headspace (including that caused by over-sizing the case) is the greatest cause of head seperations (the main reasion that guys who reload Belted Mags recogmend sizing only the neck to increase case life).
The brass that get's trimmed off comes from the entire case extruding under the pressure of firing, not from one paticular area of the case.
Some guys like a mag full of lead, I still prefer one round to the head.
Schoff14
Some reloaders use the thumb rule of "trash when they need trimming for the 5th time".
As Justen pointed out, excessive headspace (including that caused by over-sizing the case) is the greatest cause of head seperations (the main reasion that guys who reload Belted Mags recogmend sizing only the neck to increase case life).
The brass that get's trimmed off comes from the entire case extruding under the pressure of firing, not from one paticular area of the case.
Some guys like a mag full of lead, I still prefer one round to the head.
i realize it comes from the whole case. So if you know your beginning case thickness and length, you should be able to find out when your case is two thin, which is what causes the shininess.
The shininess comes from the brass reaching its elasticity point or yield point. Which means that the piece of brass as reached a stress point where it no longer goes back to where it was before.
Here is an over view of what I am talking about.
http://www2.latech.edu/~jordan/courses/me215/ManualF03/03TensileTesting.htm
So instead of making this a rule of thumb, I am saying that you can know exactly when, after you have trimmed a certain length off, your case can no longer be fired safely.
why chase the game when the bullet can get em from here?....
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