Odd reading, case length...

daved20319

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Have a Hornady Comparator, and was checking some once fired .223 brass from my Savage 12 FV. Was comparing it to the same unfired ammo, and the numbers were the same! So either no stretch, or this ammo happens to be an exact fit to my chamber. Is this common? And BTW, it is NOT accurate in this rifle, at 100 yards I'm lucky to hold 3", and at 300, even a 12" plate is a challenge. My 55 gr. reloads are far better, around an inch at 100 yards, and with the right ammo, this is a 1/2 MOA gun, at worst. The ammo is the Magtech 62 gr. FMJ, if anyone cares. Later.

Dave
 
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Was the once fired brass re-sized?
If not, it will gauge shorter(to datum)/longer case length after re-sizing.
If already re-sized when gauged...never mind.
:D
 
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OP
D

daved20319

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I guess I'm confused, why would I resize it first? The whole reason for using the comparator is to determine how much to bump the shoulder back during resizing, or have I got it wrong? Just seemed weird that fired and unfired would measure the same in this rifle, my Grendel grows about .003" when fired. Both are bolt action, BTW.
 
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I guess I'm confused, why would I resize it first? The whole reason for using the comparator is to determine how much to bump the shoulder back during resizing, or have I got it wrong? Just seemed weird that fired and unfired would measure the same in this rifle, my Grendel grows about .003" when fired. Both are bolt action, BTW.
Oh OK, you want stretch...add more powder.
FYI: lubed cases will not stretch/thin the web
jmo
:D
 
OP
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daved20319

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Not trying to be rude, but do you even know what a case comparator is used for? Your responses make no sense to me, it sounds like you're somehow confusing a comparator with a resizing die. I don't "want" stretch, I'm trying to determine how much the brass is being stretched during firing, AKA fire forming to the rifle chamber. In my Grendel, the brass "grows" about .003", in the Savage, it didn't change at all. Just seemed a little odd to me.
 
Not trying to be rude, but do you even know what a case comparator is used for? Your responses make no sense to me, it sounds like you're somehow confusing a comparator with a resizing die. I don't "want" stretch, I'm trying to determine how much the brass is being stretched during firing, AKA fire forming to the rifle chamber. In my Grendel, the brass "grows" about .003", in the Savage, it didn't change at all. Just seemed a little odd to me.


LOL.... you’re being teased.... trolled... punked..... and as the Aussies say, he’s “pissing in your pocket”.


:s0112:
 
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So you said: "I'm trying to determine how much the brass is being stretched during firing".
And you found: "in the Savage, it didn't change at all"
Seems like you answered your own question right there.
If I were you, I'd pay no attention to anything I've posted here and concentrate on the other answers you have gotten.
In fact, I suggest you just add me to your ignore list.
:D
 

Dyjital

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How did you measure your brass?

From end to end? If so that’s your problem.

Brass stretches when it’s resized. It doesn’t stretch by length when you shoot it. It expands when shot, the expansion caused length growth upon resizing.
 
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How did you measure your brass?

From end to end? If so that’s your problem.

Brass stretches when it’s resized. It doesn’t stretch by length when you shoot it. It expands when shot, the expansion caused length growth upon resizing.
It will always generally grow if you check over all length. Now, it will only stretch out as big as the chamber, but only when it's being fired. Then microseconds later, it shrinks back down a little bit. If it didn't, you would have a seized piece of brass in your chamber every time. That is the beauty of using brass for a cartridge case. I'm also thinking the OP is not using the comparator correctly... I'd use the correct size insert and measure as close to the shoulder datum point as possible..... Also, if you use the correct insert, you can check it to be sure your headspace is within spec. Again, that would be a measurement taken directly from the datum...
 
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The comparator insert should be the same as the datum point, so you know head space gap. If it really is unchanged, you may be lucky or you may have a chamber below minimum tolerances.
For .223, it would be an insert of 0.330".
 
OP
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daved20319

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The comparator insert should be the same as the datum point, so you know head space gap. If it really is unchanged, you may be lucky or you may have a chamber below minimum tolerances.
For .223, it would be an insert of 0.330".
Yup, that's the one I used. I don't think the chamber is below spec, I haven't had any issues in this rifle with a variety of ammo, both factory and hand loaded. Also, I've only checked the one brand/batch of factory ammo, maybe something else would gauge shorter, I know that's the case with the variety of Grendel ammo I have on hand.

BSA, I do understand the firing cycle of a brass cartridge case, and I'm pretty sure I'm using the comparator correctly, it's not exactly rocket science o_O. They call it a comparator for a reason, not a gauge, because it's a relative measurement comparing two different pieces of brass, rather than an absolute dimension. As I've said before, it just seems odd to me that this particular ammo seems to be a virtual exact match to my chamber headspace.

Thanks for the responses, guys, I guess I have some more research to do, verify my procedure, and check some other ammo. Later.
 
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It isn’t uncommon for the chamber to match the unfired case. Check Sammi drawings for both the cartridge and the chamber. You will notice an overlap where the cartridge can be longer than the chamber.

For 223, the cartridge could be 0.003 longer than the chamber.
Max cartridge to shoulder datum is 1.4666
Min chamber to shoulder datum is 1.4636
 

DLS

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First of all you are using the comparator correctly.

Second, Pepe-lepew is correct and most likely has described what is happening with your rifle. There are really three measurements that a reloader needs to watch that can become confused.

1. Chamber headspace
2. Cartridge headspace
3. Overall cartridge length (OAL)


When folks talk of "headspace" they are almost always referring to chamber headspace, which is the distance from the face of the closed bolt to some datam point on the chamber shoulder (usually midpoint on the slope). You can measure this indirectly with a comparator by measuring fired brass using the proper insert. Since brass flows out to the chamber dimensions (with a tiny bit of spring back once pressure drops) the exterior measurement of the brass gives an indication of chamber headspace.

Cartridge headspace is the measurement from the base of the cartridge case to some datum point on the cartridge case shoulder. You can measure this directly with the comparator. Typically cartridge headspace is a bit shorter than chamber headspace to ensure reliable chambering, but as already noted there is an overlap in allowable specs. So you can have a case longer than the chamber it's being loaded into. This usually is not a problem since the "over size" is typically very small and even with an autoloader there is enough chambering force to push the shoulder back, giving a nice tight fit of the brass to chamber. This will result in your fired brass being the same length as the chamber headspace which can, in rare circumstances result in a case with a shorter cartridge headspace measurement after it was fired as compared to before.

The real problem in chambering comes from cartridges that are too large in diameter. The amount of cartridge surface area that is contacting the chamber walls during loading results in (with an over diameter case) high enough friction to potentially keep the firearm from going into battery.

OAL is another thing entirely.

I hope this helps?
 

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