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9mm case length

37K views 35 replies 16 participants last post by  howlnmad 
#1 ·
Hello, fellow gun guys,
I just joined because I have run into something I had never run into before.
I have done reloads for quite a few years and not blown my hand or eyes off so, I know a little.
I have just recently decided to reload 9mm Lugers. My reload manuals say the typical case length is .754". On measuring some cases I find the once fired length is closer to .745" (+ or - .002). I have checked a fair number of different brand cases (I bought some once fired cases in bulk) and all are around .010" short. Does anyone here know anything about this?
Thanks for any help.
 
#3 ·
R.E., you made me curious. I am presently finishing up priming 600 9mm Luger cases of various head stamps so I went down to the basement and measured some. Picking different head stamps at random I got measurements anywhere from .746 to .750 on brass that range from once fired to "I have lost count". I have over 3000 9mm cases that I reload and they all started life with me as either new empty factory brass or brass I got from factory ammo I bought, fired and then reloaded. I hate to admit it but I have never purposely measured any of my 9mm brass. I have never trimmed any of it either. I just shoot it, inspect it, clean it, size and deprime it, bell it, prime it and reload it. So I have never been concerned with it's length. I measured some new Winchester unfired brass and it measured .747 and .746.

And Welcome to the forum.
 
#4 ·
Well, todd51, thank you for your reply. I have never run into this situation in my past reloading. It seems to me that we both have run into the same animal. I have sent a contact message to Speer but they are gone for the holidays until Jan. 5. I will tell you that I have checked 8 different manufacturers cases and all are in the 745" to 747" length. Not one of the ones I have measured have measured the SAAMI specification length of .754"
 
#35 ·
Well, todd51, thank you for your reply. I have never run into this situation in my past reloading. It seems to me that we both have run into the same animal. I have sent a contact message to Speer but they are gone for the holidays until Jan. 5. I will tell you that I have checked 8 different manufacturers cases and all are in the 745" to 747" length. Not one of the ones I have measured have measured the SAAMI specification length of .754"
[/QUOT
Well, todd51, thank you for your reply. I have never run into this situation in my past reloading. It seems to me that we both have run into the same animal. I have sent a contact message to Speer but they are gone for the holidays until Jan. 5. I will tell you that I have checked 8 different manufacturers cases and all are in the 745" to 747" length. Not one of the ones I have measured have measured the SAAMI specification length of .754"
I always understood the .754 was a max dimension.
 
#7 ·
The way it works is there is a maximum case length listed in reloading manuals and that is 0.754 inches for 9mm Luger. When the cases reach the maximum they are supposed it be trimmed back to 0.744 inches (0.010 inches shorter than max). The trim-to length 0.010 inches less than the maximum case length is typical for every one of the 30+ different cartridges I reload for. If your case fall within the range of 0.744 to 0.754 inches then you are supposedly good to go. The most recent Hornady manual I have says trim-to 0.005 inches less than the max case length but it is the only manual I have ever seen with that spec and I believe it is wrong base on 30 years of reloading experience.

But let me tell you most of my 9mm brass is stuff bought in the late 1980's. It has never been trimmed. Each case has been reloaded so many times that the head stamp is disappearing and NONE have every been trimmed. Straight wall case do not grow like necked down rifle cases. I never bother to measure the 9mm cases but just reload them again. The only ones to have been replaced are those that got lost on the ground at the range.

LDBennett
 
#9 ·
Like everyone else, I to have never measured my 9mm , 45acp or my 32acp.
Since straight wall brass really doesn't "grow" much and also being pistol ammo , I am as guilty as everyone else in not trimming or measuring the fired cases.
Up until now I've never given it much thought because I haven't had any problems ( due to case length) reloading pistol brass for the past 40 years.
 
#10 ·
I've got cases that are down to .735" that have never been trimmed. I found this out by dropping them into the barrel, removed from the gun, and seeing them disappear.
I found that when you crimp the case you have to keep the crimp to the diameter shown, specs, in the book. If you crimp the case too tight it can also fall to far into the chamber.
Also on another note, the COL for different 9mm cartridges seems to be all over the board. Not to mention the use of all the new swagged and copper plated bullets with no recipes, just keep them below 1250fps.
Any body else or is it just me?
 
#11 ·
rimmer1:

The cases should be in to the range I gave (0.744 to 0.754 inches). Too short and they will fall too deeply into the chamber and the firing pin may not be able to reach the primer with enough energy. Too long and the slide may be open enough that the disconnector will not allow the trigger to be pulled.

NEVER over crimp semi-auto ammunition. If you do the edge of the case that is suppose to stop the case from falling all the way into the chamber will not engage the chamber correctly. You also distort the bullet which may cause poor accuracy.

Plated bullets, in my experience of well over 20 years of use, should not be run at over 1000 FPS. That goes for the Rainier Plated bullet that I have been using for all those years. The same for cast bullets. Only jackets bullets or gas checked cast bullets can be driven to speeds above 1000 fps. Some here have founds that by custom sizing home cast bullets to exactly mate with the barrel (whatever that size difference is??) higher velocities can be used. For commercially cast bullet the 1000 fps limit applies, in my experience.

LDBennett
 
#12 ·
OK. To my new friends, I thank you for your replies to my inquiry. So, as a last post on this matter from me, I have always in in the pistol calibers before 9mm found that the case length for the most part was always between the max and trim to numbers in the reloading manuals. Obviously, 9mm is different in that respect. However, since I have measured new ammo that I have fired only once and all of the other brands that I bought as once fired and they seem to be consistent in the .745" to .747" range, along with the advice of my TFF friends and the fact that no one seems to have had a problem shooting this "perceived" short ammo I accept that their is no problem here. Thanks again for you interest and help, guys! R.E.
 
#13 ·
R.E.Spencer:

Your case are NOT short. They fall into the range between the trim-to length and the max length. 0.747 is between 0.744 to 0.754. The case length range need NOT be any tighter than that specified in every reloading manual (except the Hornady manual which I think to be wrong or just extra cautious). It makes no difference what new ammo or once fired cases you previously bought are but it matters what the reloading manuals says your sized cases should be. Don't confuse the max case length as the specification. The range 0.744 to 0.754 is what counts. And do not measure the cases until you sized them first. Sizing can change the case length. In fact, just load and shoot them and forget about measuring the case length. This of course doe not apply to bottle necked rifle case. They change case length drastically with firing and NEED to be trimmed regularly when they exceed the maximum listed case length after being sized.

LDBennett
 
#15 ·
Cartridge OAL (Over All Length) in pistol calibers is the most important factor in pressure levels. Seating a bullet too deeply generally increases the pressure levels. Exactly as George pointed out - straight walled pistol cases don't "grow" in length like bottle neck rifle calibers.

Just for grins-and-giggles I trim my pistol cases to the same length. I'm only reloading a hundred or so cases at a time, so it isn't a big deal for me to trim them. Just like removing the spent primer carbon from the primer pockets every time I reload - I **don't have to do it** but I do. I also tumble my cases every reloading until they sparkle and shine inside and out - I don't have to do it but I do. I just enjoy reloading. I know my ammunition is better than anything I can walk into a store and buy off the shelf.
 
#17 ·
COL should be determined BEFORE you ever start to load, much less change after you have a load. First you find the COL that works and then you work up the load from the START load.
You can seat a bullet quite deep in most cases, if you start at the start load, and have no issue.
Remember, the whole COL/pressure issue came from an article pointing out that KBs amongst LEOS at the range was traced back to LEOs who kept rechambering the same cartridge for months. They showed that a 9x19 cartridge that produced 33ksi would produce about 63ksi if the bullet was set into the case 0.25" (1/4") deeper (and 0.100" set-back was found in the top cartridge in many LEOs magazines from continually rechambering the same cartridge). THAT is beyond any COL variance a reloader will use.
So, if 0.25" set-back produces a 30ksi pressure rise, a first-order assumption would be that a 0.025" set-back would produce a 3ksi pressure rise (and that will not take a safe load to proof pressures, much less KB pressures) and a 0.0025" set-back would produce a 300 psi pressure rise.
So, first find your COL and then work up the load.
 
#19 ·
Thank you for the cited data.
Wow, that would scare anyone loading the .40 S&W. Reads more like: don't mess with the .40 S&W—walk away very slowly.
They went from about 33ksi at 1.100" COL to about 63ksi at 1.030" COL, in only 0.070" of COL change. Putting a linear "best match" curve to the data from 1.100 to 1.030" gives a linear equation that pressure = -470756x + 548193, where x is the pressure in psi, for an R^2 of 95.38%—not a bad fit at all.
However, it is important to remember that the .40S&W, as cited, was using a 180gn bullet—which really cuts into the case volume before ANY set back happens. Next, what powder were they using? TiteGroup, N310, and Clays already produce pressure spikes in 9mm and .40 and should be loaded carefully and well under max.
Yet, in the article I was citing, they reduced the COL of a standard 9x19 cartridge by 0.25" and only got about 30ksi increase.
For your data, again assuming that the pressure increase is fairly linear from 1.100 to 1.030" (when in fact, the pressure is actually going up exponentially, so the linear assumption will OVER STATE the pressure change), a 0.07" change caused a 34ksi change. So, based on that, a 0.007" change would produce about a 3.4ksi change, max. Quite a bit larger than the cited 9x19 data where the 0.25" set back raised pressure by about 34 ksi—but it doesn't make my first order assumption bad in the range I was dealing with.
Your data set shows that a 0.010" setback under those conditions will raise pressure quite a bit more, making NOT going UNDER the manual's COL and NOT starting any where but the START load even more critical. As I always say: try to find several sources of data and start at the lowest start load.
We can argue the extent, but the simple linear fit is more than good enough for our purposes.
 
#23 ·
And the article states this was NEW brass to begin with. Kind of makes you question range pickup brass. I have only had to retire a couple dozen .45acp cases because of primer seating problems. My last batch of 45acp once fired brass was truly once fired, it came from a military training range and is head stamped "MATCH" a very nice gift of 500 Cases.
 
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#27 ·
I am just being lazy - but the question of trimming pistol brass - I trim all new, unfired brass the same: I size them and trim them. I've bought enough NEW brass to know that just because it is NEW doesn't mean that it is ready to prime, charge and shoot. I've had NEW cases exceed maximum length, and also be distorted/dented from shipping.

Straight wall pistol caliber cases that have been fired/ range pick-up brass? I trim all of mine. Sometimes I am surprised how much I can trim to reach a standard measurement. Maybe I don't "have to" - I do it because I enjoy reloading and making my ammo 'extra special' IMHO.;)
 
#28 ·
Yes. I do the same by measuring my brass and trying to trim to a uniform length within tolerances if I choose to trim. Most of the time I don't trim. I just measure and chunk the ones that are too short if I can't stretch them back out to within tolerances in the sizing die. I put a chamfer on the inside of the case but not the outside as long as there are no burrs so I maintain the lip for headspace.
 
#29 ·
30 years ago I trimmed one lot of handgun brass. I have never trimmed any handgun brass since. I trim fired rifle brass (shouldered cases) when they need it. I have never in those 30 years had a single problem with new brass being too long, either rifle or handgun. This experience is based on reloading for 30 different cartridges, including both handgun and rifle brass. I suppose if you have nothing else to do then trimming brass might be fun. That is not my case, though.

LDBennett
 
#34 ·
Fairly old thread. Wonder how many of the posters are still alive? :p
I think I am alive this morning. I checked my OAL and I have lost one inch. I am in the last hole in my belt so I may be over crimped. I have reduced my load by 30 pounds and am now with in the BMI recommendations. It has been a long time since I did a "plunk test".:rolleyes:
 
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