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No. Sitting and resting my hands on the rolled up carpet things at kokohead.
why?

It will take more variability out of the grouping.  Even braced like that I assume there is more human error in there than you want.

It will take more variability out of the grouping.  Even braced like that I assume there is more human error in there than you want.

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True dat.
On the other hand, Accuracy was not my primary goal. The primary goal was to make ammo that looks and feels like the factory XTP ammo.
Good accuracy is only a pleasant perk to have. Besides, It's already a PITA to haul around and set up the chrono in addition to all the normal stuff.

Having said that, there is one other anomaly that I noticed last week. I'll tell you about it if I can duplicate the anomaly.

Going back to the 2.5 inch group I shot. I thought that was pretty good for 3.5 inch compact 9mm "carry gun"

A surprising anomaly....

Last week, when I was testing for the best accuracy with the "simulated XTP" load. I noticed that the same load specs stuffed into different shell casings had a drastic difference in point of impact. In this situation, the bullet was the 9mm 124 HAP with 4.x HP38 with a Fed GM100 primer. Test gun was a stock 3913 at 25 yds off the carpet roll at KHSC.

So I went and re-tested yesterday to confirm that it was not a fluke. ...I got the same result.

When I used Federal (FC) shell casings, the poi (point of impact) was at 8 o'clock about 2.5" from center.
When I used Winchester (WIN) shell casings the poi was 3 o'clock about 1.25' from center
See the attachment...

I am at a loss to explain why there would be such a drastic change in poi just by changing shell casings.
Velocity test showed a 1.4% difference in speed (WIN was about 16fps faster) I do not think 1.4% makes that kind of difference.

Anyone care to form a theory?

Consider the implications. If you are reloading for casual target shooting and get your shell cases all mixed up, then some shots go low-left and some shots go high-right and you get a big spread of shots all over the place automatically. And that is before you factor in human error. YIKES!

Hmm interesting I wouldn't think 16fps would do to much also. Unless you trimmed the brass to the same length could it be that the different cases have a different oal causing the crimp to be different resulting in poi difference? I'm not a pro loader but just a thought..

Hmm interesting I wouldn't think 16fps would do to much also. Unless you trimmed the brass to the same length could it be that the different cases have a different oal causing the crimp to be different resulting in poi difference? I'm not a pro loader but just a thought..

Considering the 9mm round head spaces on the case neck having the bullet embedded into the case and crimped at different places along the bullet's length I think you may be on to something here.

Could be the amount of crimp on too.  So much different areas for variances.  Unless OP is using new brass, then it takes some of the variances out of the equation.

Hmm interesting I wouldn't think 16fps would do to much also. Unless you trimmed the brass to the same length could it be that the different cases have a different oal causing the crimp to be different resulting in poi difference? I'm not a pro loader but just a thought..

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I do not trim 9mm brass. These were once fired shells. Absolutely no changes made to the dillon between the loads. Only the shells changed.
It's a mystery.

Personally, I shot almost 100% 45 auto in combat matches so supreme accuracy was never a consideration.
I was more concerned with making power factor and reliable function.
The 45 auto shoots straight with almost anything. To prove that point, I once dug 45 FMJ ball heads out of the backstop, washed them, ran them through a sizer to make sure they are sort of round, and loaded them up again. I got 25yd groups about 4". Crazy but true.
I suppose that is why I tried to avoid 9mm all these years. It is a bit more twitchy than the old 45.

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I do not trim 9mm brass. These were once fired shells. Absolutely no changes made to the dillon between the loads. Only the shells changed.
It's a mystery.

Personally, I shot almost 100% 45 auto in combat matches so supreme accuracy was never a consideration.
I was more concerned with making power factor and reliable function.
The 45 auto shoots straight with almost anything. To prove that point, I once dug 45 FMJ ball heads out of the backstop, washed them, ran them through a sizer to make sure they are sort of round, and loaded them up again. I got 25yd groups about 4". Crazy but true.
I suppose that is why I tried to avoid 9mm all these years. It is a bit more twitchy than the old 45.

I have been reloading 9mm for almost 30 years and I have never seen this. Only time I have seen a different POI is with different weight/type bullets. Even charge differences don't move the POI enough to mention. At least this is what I have seen.

Did you measure the over all case lengths between the different cases? I've noticed that different brands have had different length and being that you set up your Dillion for case "A" and didn't make any changes to it when loading case "B" if it is longer there will probably be more crimp applied or vise versa not enough crimp and like what the inspector said about the different places along the bullet's length

Did you measure the over all case lengths between the different cases? I've noticed that different brands have had different length and being that you set up your Dillion for case "A" and didn't make any changes to it when loading case "B" if it is longer there will probably be more crimp applied or vise versa not enough crimp and like what the inspector said about the different places along the bullet's length

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I just took a quick survey of the fc and win cases. This is what I see.
Generally, the thickness of the brass at the mouth is the same.
Generally the win cases are about .004" longer. I think this could be the key, but not because of the crimp.

Here is my theory:
Because the taper crimp is so gentle, .004 in. case length difference does not make the crimp change much, if at all.
However, I think .004 in. is enough to make a tighter chamber fit  This might make the bullet more concentric with the bore and thus launching the bullet into the lands a bit truer. That might also be why the poi of the win cases are really close to the correct  place.
Tighter chamber fit would also account for the increase in velocity, guaranteed.

How does that theory sound??

Seasoned rifle shooters know all about this, don't ya?

Yup that's a good theory. After fire forming brass to the headspace of the chamber and seating the bullet ~ .020-.030 off the lands depending on the rifle, by getting the case body and bullet to line up with the center of the bore will help with concentricity and lead to better accuracy. I noticed it helped with my .308. But if any one of these are off along with case neck tension it can throw off accuracy that's why I thought maybe your crimp could of been causing the problem. But with only .004 difference I doubt the crimp is the problem either.

This is about the end of the project. After testing loads for about a month, I got a decent powder charge.
My buddy tried a sample and it was ok with him, so I started busting into those precious boxes of XTP heads.
pic 1 is after cleaning the lube off the ammo.
pic 2 is checking for high primers and the max cartridge gauge for checking for proper chambering

Bonus Rounds:

Just for fun, I loaded some XTP heads at what might be considered "+P" levels.
I achieved velocities approx. 15% to 20% higher than the factory XTP load.
When using lightweight 9mm heads and medium/slow Aliant flake powder, Sometimes the powder charge is compressed by the head when seating.
Sometimes the powder overflows and you have to tap the shell to get it in, then smash the head on top.

In this case it was not so bad. The powder charge was the max listed for UNIQUE. The powder is only slightly compressed.
see pic

I hope all you newbie 9mm reloaders found this thread to be informative. Happy loading.

thanks for all the info!!! It seems like a trial and error to find the right combination...

A surprising anomaly....

Last week, when I was testing for the best accuracy with the "simulated XTP" load. I noticed that the same load specs stuffed into different shell casings had a drastic difference in point of impact. In this situation, the bullet was the 9mm 124 HAP with 4.x HP38 with a Fed GM100 primer. Test gun was a stock 3913 at 25 yds off the carpet roll at KHSC.

So I went and re-tested yesterday to confirm that it was not a fluke. ...I got the same result.

When I used Federal (FC) shell casings, the poi (point of impact) was at 8 o'clock about 2.5" from center.
When I used Winchester (WIN) shell casings the poi was 3 o'clock about 1.25' from center
See the attachment...

I am at a loss to explain why there would be such a drastic change in poi just by changing shell casings.
Velocity test showed a 1.4% difference in speed (WIN was about 16fps faster) I do not think 1.4% makes that kind of difference.

Anyone care to form a theory?

Consider the implications. If you are reloading for casual target shooting and get your shell cases all mixed up, then some shots go low-left and some shots go high-right and you get a big spread of shots all over the place automatically. And that is before you factor in human error. YIKES!

Thank you for all the great info! 

My theory would be that the different brass might be of a significant different volume.  In rifle reloading this is a know factor.  In a tiny case like 9mm, a slight difference in case volume could mean a great difference in pressures, causing such POI and accuracy shifts. 

In a voluminous case, such as .45acp, this would not matter as much. However, in 9mm the higher pressures and smaller volume could be why it is so "finicky".  My $.02... 

Also to add, if you play with seating depth, just a little, you can move those groups around as well.

Thank you for all the great info! 

My theory would be that the different brass might be of a significant different volume.  In rifle reloading this is a know factor.  In a tiny case like 9mm, a slight difference in case volume could mean a great difference in pressures, causing such POI and accuracy shifts. 

In a voluminous case, such as .45acp, this would not matter as much. However, in 9mm the higher pressures and smaller volume could be why it is so "finicky".  My $.02... 

thanks heavies
your theory makes sense

Thank you for all the great info! 

My theory would be that the different brass might be of a significant different volume.  In rifle reloading this is a know factor.  In a tiny case like 9mm, a slight difference in case volume could mean a great difference in pressures, causing such POI and accuracy shifts. 

In a voluminous case, such as .45acp, this would not matter as much. However, in 9mm the higher pressures and smaller volume could be why it is so "finicky".  My $.02... 

Also to add, if you play with seating depth, just a little, you can move those groups around as well.

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I just noticed this reply years after posting.
Yes it does make sense.

In theory, it makes sense. For rifle, I've seen where it makes little difference, at least for 223.

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I just noticed this reply years after posting.
Yes it does make sense.

I agree with Heavies.
Try weighing the cases.
Heavier case thicker wall ?
Thicker wall, less space inside.

I agree with Heavies.
Try weighing the cases.
Heavier case thicker wall ?
Thicker wall, less space inside.

...
Ya know this was 4 years ago.
I'll try weighing somè shells anyway .