9mm case length and accuracy

[lordpaxman]

In an other thread, a member posted this article:
http://www.lasc.us/TaylorSecrets9mm.htm
The author ran a series of tests on case length and found a case length of .750” gave the best grouping.
With the volume I load I’m most likely not going to be measuring case length but I found the data interesting and was wondering if anyone else has corroborated this? I may at least add this to the measurements during load development.

 

[Rule3]

In an other thread, a member posted this article:
http://www.lasc.us/TaylorSecrets9mm.htm
The author ran a series of tests on case length and found a case length of .750” gave the best grouping.
With the volume I load I’m most likely not going to be measuring case length but I found the data interesting and was wondering if anyone else has corroborated this? I may at least add this to the measurements during load development.

I would think Live Life (bds) would be doing a Myth Busting presentation on this.

 

[Blue68f100]

In general with cases that headspace off the mouth do better with near max length (<0.003") brass. The reason is a better seal to the chamber, less movement when hit with FP. This helps minimize ES, and lowers SD. But you have to be really really go to see the difference.

 

[red rick]

I would think OAL would make more of a difference than case length .

 

[Walkalong]

……….. But you have to be really really good to see the difference.

That’s where I am at with it.

 

[WeekendReloader]

I've trimmed 9mm brass. The first thing I noticed is that once fired factory brass is not consistent in length and the case mouth is not even. I could see that sometimes only half of the case mouth was touched by the trimmer. Sometimes, the trimmer would slice away a lot of brass. Very inconsistent.

My thought in trimming the brass to a consistent length was that the sizing, flaring, seating and taper crimp would be consistent.
I have since loaded a bunch of mixed range pick-up brass without trimming and it all loaded and shot just as good as the trimmed brass. I guess I'm not accurate enough off-hand to see a real-world difference in performance.

 

[DMW1116]

After testing a fair number of different loads in 9mm, this was probably going to be my next step. I'm pretty much convinced I'm not a good enough shot to see the difference now, so I'll wait a bit. Range brass is all over the place length wise, so trimming it all the same would make it all equally short. I'd have to buy some new 9mm brass to really get a good starting point. If I won't be able to tell anyway, I'll probably pass. Then again, curiosity might get the better of me, both in relation to accuracy of the rounds and if I can see it or not.

 

[GeoDudeFlorida]

The only time I trim 9mm is if I'm making it into something else, like 9mmMak.

 

[redcon1]

I'm sure it wouldn't lead to less accuracy. I would need a more compelling reason than that to trim 9mm brass however. Maybe if I knew my time here on earth was unlimited but it ain't.

 

[LiveLife]

The author ran a series of tests on case length and found a case length of .750” gave the best grouping.

I found the data interesting and was wondering if anyone else has corroborated this?

I would think Live Life (bds) would be doing a Myth Busting presentation on this.

In theory yes and I have considered doing a longer vs shorter resized brass myth busting thread but as pointed out by other members, with reloading/shooting variables that will be in play, I am not sure if we could isolate the variable of case length alone to stand out to make a successful myth busting thread.

The reason is a better seal to the chamber, less movement when hit with FP. This helps minimize ES, and lowers SD. But you have to be really really go to see the difference.

That’s where I am at with it.

In actuality, longer cases headspace off case mouth and shorter cases loaded to same OAL/COL will start to headspace off extractor (Imagine bullet nose/case mouth dangling in the air away from chamber ).

When primer flash ignites powder charge (For magazine fed semi-autos, powder charge will be tossed "powder forward" when chambered), burning gas will expand case neck and case mouth sealing against chamber wall. If longer case mouth is in contact with chamber, sealing of gas will be quicker but shorter case will be pushed back against breech wall face and more gas will leak around the case mouth/neck before sealing with chamber wall.

So based on this, longer cases should produce more consistent chamber pressure build, which will produce more consistent maximum pressures for more consistent muzzle velocities in terms of SD/ES ... ultimately leading to smaller groups on target. BUT, will this variable be large enough to overshadow other reloading and shooting variables to show on target? As Walkalong and Blue68f100 pointed out, we may not be "good enough" to show the difference.

I can certainly choose the longest and shortest resized cases to see if I can produce difference on paper (I probably could produce smaller groups with longer cases) but since I do not trim straight wall semi-auto pistol cases nor sort by resized case lengths (Like most reloaders here on THR), I will default back to checking neck tension of finished rounds by measuring bullet setback after being fed/chambered from the magazine (Which IMO carries far greater reloading variable to overshadow other reloading/shooting variables to matter on group size).

Sometimes, an OCD reloader must know his limitations.

So I will tip my hat that if you got to where you have isolated and eliminated enough reloading and shooting variables to see difference from resized 9mm case lengths; sure, go ahead and sort by longest resized case lengths but by all means, do not trim 9mm brass.

 

[Walkalong]

I shot mixed 9MM brass for years and it did fine, but seemed to have the occasional what the heck shot. Since I have so much 9MM range brass I finally decided to sort some and shoot one headstamp. I had already proven to myself that one headstamp 9MM brass shot better than mixed, so when my 9MM needs went more from blasting to serious plinking informal target shooting, I wanted my reloads to be more consistent.

I will not be going the next step and sort by headstamp and case length, regardless.

 

[243winxb]

Precision pistol competitors, shooting 45acp @ 50 yards, have known for years, the long brass shoots best when of the same lot.

 

[Blue68f100]

In theory yes and I have considered doing a longer vs shorter resized brass myth busting thread but as pointed out by other members, with reloading/shooting variables that will be in play, I am not sure if we could isolate the variable of case length alone to stand out to make a successful myth busting thread.


In actuality, longer cases headspace off case mouth and shorter cases loaded to same OAL/COL will start to headspace off extractor (Imagine bullet nose/case mouth dangling in the air away from chamber ).

When primer flash ignites powder charge (For magazine fed semi-autos, powder charge will be tossed "powder forward" when chambered), burning gas will expand case neck and case mouth sealing against chamber wall. If longer case mouth is in contact with chamber, sealing of gas will be quicker but shorter case will be pushed back against breech wall face and more gas will leak around the case mouth/neck before sealing with chamber wall.

So based on this, longer cases should produce more consistent chamber pressure build, which will produce more consistent maximum pressures for more consistent muzzle velocities in terms of SD/ES ... ultimately leading to smaller groups on target. BUT, will this variable be large enough to overshadow other reloading and shooting variables to show on target? As Walkalong and Blue68f100 pointed out, we may not be "good enough" to show the difference.

I can certainly choose the longest and shortest resized cases to see if I can produce difference on paper (I probably could produce smaller groups with longer cases) but since I do not trim straight wall semi-auto pistol cases nor sort by resized case lengths (Like most reloaders here on THR), I will default back to checking neck tension of finished rounds by measuring bullet setback after being fed/chambered from the magazine (Which IMO carries far greater reloading variable to overshadow other reloading/shooting variables to matter on group size).

Sometimes, an OCD reloader must know his limitations.

So I will tip my hat that if you got to where you have isolated and eliminated enough reloading and shooting variables to see difference from resized 9mm case lengths; sure, go ahead and sort by longest resized case lengths but by all means, do not trim 9mm brass.

I don't trim pistol brass either. But I did take the time to measure and sort out my 45acp brass looking for the long ones. Took several days to go through 3k mixed brass. Out of the lot I only got around 150 cases that fit the criteria. What a waste of time, won't do that again. Surprisingly most of the ones fitting criteria was PPU brass.

 

[BJung]

I'm the one that probably posted the thread the OP cites. I've never trimmed pistol brass before but plan to. I enjoy experimenting and finding ways to increase the accuracy of my reloads. I have bags of range brass, have separated them by brand and plan first so I can load 10 or 5 rounds of each length to test. I'll also trim others so I have increments of a certain range. And, I will test accuracy by seating depth too. I just haven't got around to it. I never shoot my test loads standing because of increased error instead shoot from a sandbag.

 

[Otto]

In an other thread, a member posted this article:
http://www.lasc.us/TaylorSecrets9mm.htm
The author ran a series of tests on case length and found a case length of .750” gave the best grouping. ….

I read the above article and this sentence caught my eye….“All loads with HERCULES BULLSEYE POWDER”.

It should be noted that Hercules powders were discontinued 27 years ago. So when was the article written?

 

[CQB45ACP]

I've trimmed 9mm brass. The first thing I noticed is that once fired factory brass is not consistent in length and the case mouth is not even. I could see that sometimes only half of the case mouth was touched by the trimmer. Sometimes, the trimmer would slice away a lot of brass. Very inconsistent.

My thought in trimming the brass to a consistent length was that the sizing, flaring, seating and taper crimp would be consistent.
I have since loaded a bunch of mixed range pick-up brass without trimming and it all loaded and shot just as good as the trimmed brass. I guess I'm not accurate enough off-hand to see a real-world difference in performance.

I’ve never trimmed any brass nor do I plan to. But, I have two (yes, just two) 9mm cases that are too long to pass a gauge and I can’t bring myself to simply trash them.

 

[DMW1116]

I’ve never trimmed any brass nor do I plan to. But, I have two (yes, just two) 9mm cases that are too long to pass a gauge and I can’t bring myself to simply trash them.

Same here. I figure I’ll keep them until I have enough for a full magazine then trim them and see what happens.

 

[GeoDudeFlorida]

Same here. I figure I’ll keep them until I have enough for a full magazine then trim them and see what happens.

Switch your display to SI and mic them. Maybe you’ve got a couple of 9x21mm?

 

[lordpaxman]

I have since loaded a bunch of mixed range pick-up brass without trimming and it all loaded and shot just as good as the trimmed brass.

The article wasn’t so much about trimming as it was measuring and selecting known lengths with the .750” brass showing the best results for 9mm at 25 yards. What would be interesting to know is what the “random” population was in his test, and also the “.003” population. I’m not going to be trimming 9mm brass, or any TC brass for that matter.

So based on this, longer cases should produce more consistent chamber pressure build, which will produce more consistent maximum pressures for more consistent muzzle velocities in terms of SD/ES ... ultimately leading to smaller groups on target.

I’ll agree with you that a longer case that headspaced on the mouth would most likely produce better SD/ES, but with 9mm at 25 yards I’m not sure that’s the factor that leads to smaller groups on target. I’ve had really bad SD/ES loads that produce superior groups.

The article had .750” cases produce a 2.6” group and .743” produce a 5.6” group which is crazy to me. If and when the component shortage abates I’m tempted to run a case length vs accuracy test. If there is a relationship it’d be interesting to fathom what the accuracy mechanism is.

 

[runner3264]

9mm will hardly ever seal off at the headspace. Most cases are .010 shorter than SAAMI specs and then manufactures add many more thousandth of an inch longer chamber length than that. Most case will seal off on the diameter of the chamber than they will at the headspace.These aren't rifle cases they are pistol. My opinion is that pistol cases sealing off at the headspace or length of the case is a misconception.

 

[Nature Boy]

I will not be going the next step and sort by headstamp and case length, regardless.

Me either. My pistol skills were trained to the army standard to be just good enough to qualify expert, which is to say, not very good.

Certainly not at @Walkalong level given some of the targets he’s posted

 

[DMW1116]

Switch your display to SI and mic them. Maybe you’ve got a couple of 9x21mm?

Im pretty sure they were stamped 9x19 but I’ll check. The vast majority of the brass I pick up is shorter than trim length. I’ve had 3 cases out of about 1500 I’ve reloaded that were longer than max. I started reloading 9mm in August of 2020 so it’s only been a bit over a year.

 

[Rule3]

In theory yes and I have considered doing a longer vs shorter resized brass myth busting thread but as pointed out by other members, with reloading/shooting variables that will be in play, I am not sure if we could isolate the variable of case length alone to stand out to make a successful myth busting thread.


In actuality, longer cases headspace off case mouth and shorter cases loaded to same OAL/COL will start to headspace off extractor (Imagine bullet nose/case mouth dangling in the air away from chamber ).

When primer flash ignites powder charge (For magazine fed semi-autos, powder charge will be tossed "powder forward" when chambered), burning gas will expand case neck and case mouth sealing against chamber wall. If longer case mouth is in contact with chamber, sealing of gas will be quicker but shorter case will be pushed back against breech wall face and more gas will leak around the case mouth/neck before sealing with chamber wall.

So based on this, longer cases should produce more consistent chamber pressure build, which will produce more consistent maximum pressures for more consistent muzzle velocities in terms of SD/ES ... ultimately leading to smaller groups on target. BUT, will this variable be large enough to overshadow other reloading and shooting variables to show on target? As Walkalong and Blue68f100 pointed out, we may not be "good enough" to show the difference.

I can certainly choose the longest and shortest resized cases to see if I can produce difference on paper (I probably could produce smaller groups with longer cases) but since I do not trim straight wall semi-auto pistol cases nor sort by resized case lengths (Like most reloaders here on THR), I will default back to checking neck tension of finished rounds by measuring bullet setback after being fed/chambered from the magazine (Which IMO carries far greater reloading variable to overshadow other reloading/shooting variables to matter on group size).

Sometimes, an OCD reloader must know his limitations.

So I will tip my hat that if you got to where you have isolated and eliminated enough reloading and shooting variables to see difference from resized 9mm case lengths; sure, go ahead and sort by longest resized case lengths but by all means, do not trim 9mm brass.

But it is good to know that you put "some" thought into this.

 

[gifbohane]

I I finally decided to sort some and shoot one headstamp. I had already proven to myself that one headstamp 9MM brass shot better than mixed, so when my 9MM needs went more from blasting to serious plinking informal target shooting, I wanted my reloads to be more consistent.

Walk-
What headstamp did you settle on for 9mm? And may I ask why?

I use WIn, Blazer, and GFL, and the store the rest.

 

[Walkalong]

I chose FC because I had a crap load of in the first 5 gallon bucket.

I have done testing with Blazer, like it just fine. Thought I was going to find more of it in the first bucket, would have used it. I have picked up a ton of it over the years

No issues with the Win and GFL cases either.