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unclenick,
Are you measuring your brass after sizing?
Of course. The comparison is new to old. Many folks have reported the same observation with 45 Auto.

Here's the illustration I created some years ago to show where growth occurs during resizing a rifle case. Follow the black dots on the case to see where brass flows.

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But there is an important distinction to make. Below is an illustration of a rifle case exaggerating pressure ring formation. This case is an oddball foreign-made case that has thick walls after the head that extend further than normal so the pressure ring is further forward than normal. The illustration shows what is happening inside.

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This significance is that the lion's share of stretching results from the thin-walled portion of the case forward of the ring is clamped to the chamber by pressure during firing and while the head is still forward and out of contact with the bolt face. The pressure continues to grow until the force it applies to the head web pushes the head back into contact with the bolt face. But because the thinner-walled portion has stuck to the chamber while the pressure has not yet got high enough to stick the thicker-walled portion at that point, in order for the head to reach the bolt face, stretching of the bocy commenses at the interface between the stuck and as-yet unstuck portions of the case. That stretch adds to the length of the body by the amount of the head clearance excess headspace in the chamber allows—usually just a thousandth or two. When you resize, as in the first illustration, the amount by which the that has added to the case body height causes the shoulder to meet the die shoulder early, so that when the sizing die tries to put the case back to original dimensions, that stretched area acts like stilts, making the shoulder taller. That, added to elongation by die squeezing, forces brass to extrude upward where it flows brass from the shoulder up into the neck. The neck, being narrower than the case body, has to get longer than the case body did to accommodate at that brass.

You can prove the above to yourself. Try neck sizing only. You will find it does not grow cases significantly. Sure, you will get a thousandth or two as the case gets closer to fully conforming to the chamber's size over several load cycles, especially the first one, but not nearly what shooting FL resized brass produces. Lacking the headspace clearance between the bolt face and breech face, there is little space for the case to stretch to.

That, finally, brings us to cases at pressures too low to stick the brass to the chamber wall before pressure backs it up into the breech face. Where is the pressure ring then? There is none. The only stretching then is widening to fill the chamber. This can produce brass to be squeezed back a little longer than original with loads right on the pressure edge or that are hot enough to cause sticky extraction in a revolver, but mostly because the brass isn't stuck to the chamber walls as the case expands, the extra brass needed to fill that space is obtained by pulling the mouth back, shortening the case.

If the cases are getting shorter, where is the brass going?
When fired, the case expands to the chamber and the mouth seals to the chamber wall to prevent gases from venting. When resized the brass is squeezed back to it's original diameter and the cartridge lengthens because the mouth is the only unsupported area of the case.
I have a set of spools that limit the travel of my trimmer so I don't have to make any adjustments. I put in the proper spool and trim. I run every round through the trimmer after sizing because it is faster than using calipers to check the length. If the cases got shorter then no trimming would occur after the first firing. In 50 years of reloading I have never experienced a fired case getting shorter. I do know that unsized cases are shorter than after sizing. I also experience trimming is performed on cases after multiple firing and sizing.
In the 45 Auto, the chamber is tapered but the carbide resizing dies we use are not. They form the case straight back at the diameter needed to hold a bullet in the mouth, the only exception being due to the mouth radius and taper not moving it back quite so far. A consequence of this is that there is more expansion into the chamber when reloaded brass is fired, due to coming out of that carbide ring. A second factor with 45 Auto is the case begins to thicken about 0.35" below the mouth to be thick enough to contain pressure in an unsupported chamber, so most of the expansion from firing is forward of that. When the sizing die runs over the case, friction tries to push that expanded portiont back over the thicker part. It can't really do that, but a tiny amount of rearward brass flow results where the thickness differences meet, nonetheless.

This all depends on the pressures you are loading to. The higher they are and the faster the powder reaches them, the more likely you are to expand the brass to the sticking pressure level faster than inertia will allow the pressure to back the case up, the more likely you are to see stretching.

I bought a Lee trimming cutter when I started reloading and got the 45 Auto, 38 Special, 357 Magum and .44 Special gauges and holders to go with it. 357 Magnum would let me trim cases this way some of the time and some new cases were long enough to trim, but I don't think I could ever get the cutter to touch the other three rounds after they were no longer new. Keep in mind that in the '70s and '80s, I was mainly interested in bull's-eye target shooting, so the pressures were low in my non-magnum rounds. Nonetheless, cast an eye around on this and other shooting boards and you will find lots of folks report they never trim handgun brass because it doesn't grow significantly. The long revolver cases don't shrink like the 45 Auto, which supports my contention that the chamber taper and the short length from the mouth to the thickening portion of 45 Auto case walls and the one-diameter carbide resizing rings combine to be responsible for the observed rearward brass flow. The cases didn't get any lighter during my experiement.

As to your cases all growing, that, again, depends on how warm you load them and on the diameters of your chambers. You might try an experiment with not trimming and measuring the change over the course of several reloads, assuming they all stay within safe limits. The idea is to see if they grow by the same average amount per load cycle over time. If not, it is possible that flexure and flow from mouth flaring can move enough brass for a trimmer to pick a little up. It would be interesting to see if it settles. If you now what sorts of pressures you are developing, that would be interesting to learn, too.[/QUOTE]
 

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My 9mm die is a carbide die. It has two carbide rings. One to size the base of the case and the other sizes the neck. 54% of once fired brass will trim with some just cleaning up the mouth of the case to square. I call that trimming, any amount of brass removal is trimming in my mind. Since my trimmer is not adjusted with the exception of adding the proper spool for the case I am trimming. The spool keeps the case lengths from changing due to minor differences in adjustments.
I am not sure what "significant growth" is to anyone else but if brass is cut the cases have been trimmed. If they don't grow the trimmer will not cut brass. With my setup any growth is trimmed.
 

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The Hog Whisperer (Administrator)
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So if Nick counted 50 firings, and the cases were measured as 0.025" shorter, then wouldn't it be fair to conclude that the cases did indeed shorten about 0.0005" each firing cycle?
 

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Right. My trimmers made no contact with the 45 Auto after they were new and trimmed once for consistent crimping. The 45 Auto has less than a third of the taper rate of the 9 mm, so it is easier to size fairly straight. Also, with light target loads, the case doesn't really expand much in the lower half.

I haven't run into double-ring 9 mm sizing dies, but that doesn't mean much since I don't own a 9 mm. I have seen it commented that the Lee 9 mm die sizing ring is rather longer than its other handgun die rings, so I suspect it has some taper ground into it. ShooterPaul, whose die are you using?

To me, significant growth is something that affects either the gun (too long and raising pressures) or performance on the target. In other words, something that can't be ignored without consequence.
 

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Unless the case exceeds max length, why trim?
Trimming and cleaning are not that important for all the time spent worrying about them.
For cases that head space on the case mouth, it is really easy to run some tests and find that increasing the head space gap by trimming causes groups to open up.
So, trim cases all you want, but you may be losing accuracy if they are semi-auto pistol cases.
 

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WOW!!!! And my wife makes jokes about my OCD reloading precision,... some of you guys make me feel almost normal!:LOL:

OP,... if the case is too hard to cut, it may be work hardened,... anneal as suggested above, and you should be good to go!

All the best.
 
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