Brass shrinkage

pinne65

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Does pistol brass shrink after firing?

My unfired Starline 10mm brass measures ~ .985 +/- 0.005, after firing it's 2-3/1000" shorter.
Is this normal?
Load is 11gr Blue Dot under 180gr JHP.
 
Last edited:

Reno

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Sort of.

From the technical specs after firing the brass expands. Forming to the chamber. Which is larger than the case. This can appear to be shrinkage until you resize.

Once you resize, that expanded brass is squeezed back forward, where often, it actually gets longer.

Hope this makes sense.
 

thorborg

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Does pistol brass shrink after firing?
My unfired Starline 10mm brass measures ~ .985 +/- 0.005, after firing it's 2-3/1000" shorter.
Is this normal?
Load is 11gr Blue Dot under 180gr JHP.
So your brass is .985 +/- .005.
You indicate your after firing the brass is .002 to .003 shorter. Does this also come with a +/- .005 tolerance or did you mark the unfired brass exact length to know where it fit in the +/- spec after firing otherwise I don't see how the numbers tell the tale.

Regardless of the numbers, yes it likely did shrink and is normal.

The windy part: most of little importance to 10 mm; but I'm sort of house bound for a couple of dayso_O The larger your chamber is the more the brass will expand when fired (albeit minutely).
The more it expands, the thinner and shorter it becomes. (again minutely, and likely not proportionately)
Whether firing, or resizing, the brass has to go somewhere, or come from somewhere. Resizing, squeezes the brass back to spec inward (if you didn't have too much head space) but does not control the length so usually leaving it a little longer and a little thinner just because. Neck sizing only will usually show less length change because the body can slump some.
The ambiguity for the specifics of moving material is controlled or influenced by the varied brass shapes, straight to bottleneck, also if it is FL sized, or just necked.
Unless radically altered by changing caliber size or shape, most standard loads used in once fired brass will maintain enough thickness throughout its reload life as not to worry about it though may be worth noting from time to time to see what's going on.
That leaves hardness and length. I've rarely needed to trim length throughout the life of the brass, because, for little good reason, my first reload after resizing I bring down to minimum length, this not always a necessary thing for some unless you use it in a variety of same caliber guns. (I don't do this with 45acp)

Fl Resizing, and fired expansion, particularly in an extra large chamber, make brass brittle (work harden). Schedules for annealing brass vary according to alloy and amount / frequency of stress applied, also different between caliber / brands, loads used. All in all, as an example, in general, and though I have, I rarely need to anneal my 45-70 loads nor my 45acp in the life of the brass. I need to anneal .270 brass if Full length sizing, about every four reloads, depending on the brand of brass, more or less. However, I neck size only since it is used in the same gun, so rarely anneal in the life of the 270 (and similar fast calibers), though I might get a couple more loads if I did, I choose not to unless I see premature cracks on some lessor quality brass I'll anneal the (brand) batch to see if that abates it..
This opine on my case prep is for my hunting, and target shooting for hunting. Proved "Good Enough" (for me) over a half century. Its also as good as I can shoot.
If I needed to be more specific where the bullet goes, consistently, I had the ability to shoot, I would want my brass to be as close to perfect clones in all physical aspects as I could get them using any tool, machine, cheater I could muster up. Still, there would be a lot of shot placement variables, but ruling out the case, wouldn't be out of line for most.
A word of caution for neck size only; Early on when brass is still fairly supple, sometimes neck size only will cause the lower portion of a long case to "pooch" because of less support when being squeezed from the top only, making measuring and more importantly chambering the resized brass in your gun to see it fits.
 
So your brass is .985 +/- .005.
You indicate your after firing the brass is .002 to .003 shorter. Does this also come with a +/- .005 tolerance or did you mark the unfired brass exact length to know where it fit in the +/- spec after firing otherwise I don't see how the numbers tell the tale.

Regardless of the numbers, yes it likely did shrink and is normal.

The windy part: most of little importance to 10 mm; but I'm sort of house bound for a couple of dayso_O The larger your chamber is the more the brass will expand when fired (albeit minutely).
The more it expands, the thinner and shorter it becomes. (again minutely, and likely not proportionately)
Whether firing, or resizing, the brass has to go somewhere, or come from somewhere. Resizing, squeezes the brass back to spec inward (if you didn't have too much head space) but does not control the length so usually leaving it a little longer and a little thinner just because. Neck sizing only will usually show less length change because the body can slump some.
The ambiguity for the specifics of moving material is controlled or influenced by the varied brass shapes, straight to bottleneck, also if it is FL sized, or just necked.
Unless radically altered by changing caliber size or shape, most standard loads used in once fired brass will maintain enough thickness throughout its reload life as not to worry about it though may be worth noting from time to time to see what's going on.
That leaves hardness and length. I've rarely needed to trim length throughout the life of the brass, because, for little good reason, my first reload after resizing I bring down to minimum length, this not always a necessary thing for some unless you use it in a variety of same caliber guns. (I don't do this with 45acp)

Fl Resizing, and fired expansion, particularly in an extra large chamber, make brass brittle (work harden). Schedules for annealing brass vary according to alloy and amount / frequency of stress applied, also different between caliber / brands, loads used. All in all, as an example, in general, and though I have, I rarely need to anneal my 45-70 loads nor my 45acp in the life of the brass. I need to anneal .270 brass if Full length sizing, about every four reloads, depending on the brand of brass, more or less. However, I neck size only since it is used in the same gun, so rarely anneal in the life of the 270 (and similar fast calibers), though I might get a couple more loads if I did, I choose not to unless I see premature cracks on some lessor quality brass I'll anneal the (brand) batch to see if that abates it..
This opine on my case prep is for my hunting, and target shooting for hunting. Proved "Good Enough" (for me) over a half century. Its also as good as I can shoot.
If I needed to be more specific where the bullet goes, consistently, I had the ability to shoot, I would want my brass to be as close to perfect clones in all physical aspects as I could get them using any tool, machine, cheater I could muster up. Still, there would be a lot of shot placement variables, but ruling out the case, wouldn't be out of line for most.
A word of caution for neck size only; Early on when brass is still fairly supple, sometimes neck size only will cause the lower portion of a long case to "pooch" because of less support when being squeezed from the top only, making measuring and more importantly chambering the resized brass in your gun to see it fits.

Holy smokes, dude! That post is so long that it may just qualify for another book of the Bible right there! :eek:





The reloading bible, that is!!

;):D
 
OP
pinne65

pinne65

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So your brass is .985 +/- .005.
You indicate your after firing the brass is .002 to .003 shorter. Does this also come with a +/- .005 tolerance or did you mark the unfired brass exact length to know where it fit in the +/- spec after firing otherwise I don't see how the numbers tell the tale..
Thanks for making me double check! Didn't do a good job neither measuring nor calculating - new brass should be .9856 +0.0014/-0.0016 sampled 10 / 1000. I didn't do a before and after firing comparison. I accidentally mixed some of my new fired brass w some of the old and tried sort the two out by among other things measuring case lengths. Measuring the fired brass without depriming is hard but an unscientific 2nd check seems to suggest it actually shortens more like 0.005 to 0.006 or 0.0055 +/- 0.0005 at least for me using a Lonewolf aftermarket barrel.
but I'm sort of house bound for a couple of dayso_O The larger your chamber is the more the brass will expand when fired (albeit minutely).
Also been stuck at the house with nasty chest cold for a week. But one day I might compare LW to regular Glock shrinkage.
 
OP
pinne65

pinne65

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Your best bet is to fire it until the neck splits.

That’s how you know it’s no good.

I haven’t run into pistol brass yet that’s needed a trim. That’s counting .357 and hot .44 Mags.
Yep - waited for'em to split - and they did
split.jpg


Unfortunately on my 2nd 1000 batch of 10mm I got this idea it all needed to be trimmed down to min (don't ask me why!!!)
I've since joined the no-trim bandwagon for straight walls.
 

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