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Discussion Starter #1 (Edited)
I made up a variety of different variations of 9mm ammo, all with Delta 115gr FMJ bullets. I chrono'd each one. The loads are conservative; I'm not pushing the envelope.

My interpretation of the data is in a following post. Here's the data:





I used two different brass headstamps (Win and RP), some crimped using the Lee die, some not, different powders, different loads. The last two lines were by comparison using some rounds I'd already loaded earlier, which I could separate by headstamp.

The things to look at are equivalent load, headstamp, powder with crimp and not crimped, also to look at how the velocities tighten up as the charge increases, and the differences between headstamps.

Short conclusion: The crimp seems to make a difference in consistency of velocity, but mostly at the higher charges.

There appears to be a couple apparent light charges that really inflate the spread and SDs. That would be on lines 9 and 10.

I'll try to do a formal interpretation/writeup of what the data says later today.

I'd also be interested in others indicating what kind of consistency of velocity one should be able to achieve with handloading rounds like this.
 

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What I see, & have experienced myself, crimping gives you smaller SD which indicates a more uniform powder burn. This doesn't always mean better accuracy but often that is the result. The biggest reason for me to crimp is reliability. Taper crimped ammo just runs smoother than not crimping.
 

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And if anyone can do a screen snapshot to turn this into a .jpg and email that to me so I can insert the image directly into the post, I'd appreciate it.

I'd also be interested in others indicating what kind of consistency of velocity one should be able to achieve with handloading rounds like this.
If you will PM me your e-mail address I'll send you your jpg. The e-mail feature in the forum doesn't allow attachments as far as I can tell.

Just looking over your data I don't think you'll be able to draw many conclusions with statistical analysis. You might be able to say something like RP/BE/4.2/y @ 1088/39.4 is a lower velocity loading than RP/UNQ/4.9/y @ 1192/23.3. Other than that, conclusions will be difficult to draw because possibly there is no difference or because your sample sizes are too small.

One casual observation I've made comparing crimped reloads to factory ammo like WWB is that while the brass from factory stuff scatters over a fairly wide area requiring me to move around to pick it up, my reloaded brass will often fall in a small area allowing me to walk over and pick up 80-90% of it without moving. My groups on paper are about the same but my groups on the ground are much tighter. What's it mean? Beats me, but if nothing else it's easier on my back.
 

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Thank you for sharing those results. I rarely have access to a chrono, and I use 115 FMJ & TG loads, so that data is very helpful to me. I have settled on 4.4 grains of TG for my primary practice/target/game load. I load up to 4.7 grains to help replicate my SD load.
 

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Discussion Starter #5 (Edited)
First, let me note that I view this as preliminary data. Any conclusions I draw I will try to replicate, to see if they hold.

For now, though, I think there are several conclusions suggested by the data.

First, generally the crimped cartridges performed better in terms of consistency of results.

In most cases (lines 3/4, 5/6, 7/8, 11/12, 13/14, 15/16), the crimped rounds were more consistent, both in spread and standard deviation.

Not so with 1/2 and 9/10. In each case there was a significant outlyer that skews the results. When you remove it (dropping the number to 4 observations), it doesn't really change much. I don't know why the pattern wouldn't extend to these two, except for one thing: In each case, it was the first set of cases I filled with that powder. While I weighed a lot of charges to ensure I was on target, I didn't weigh them all.

But the others are clearly showing that the crimp reduces variation. This is probably most easily seen in the standard deviation numbers.

Second, the crimp does *not* increase pressure; it's kind of shocking how close the means are to each other, in each pair. In fact, the pressures for crimped rounds are slightly lower than the non-cromped rounds.

Third, the headstamp doesn't seem particularly related to any conclusions. In some cases it seems to matter, then the next set of pairs doesn't confirm it.

Fourth, more grains does result--generally--in higher velocities. The exception again is the first two rows, where we have higher velocities than the expected values.

I'll do this again and see if the results confirm, but for now, I'm happy doing the crimp. I think it results in more consistent results.
 

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Good stuff, thanks!
How can one figure out case pressure by reading the numbers; higher velocity=higher pressure?
I'll continue to crimp my rounds.
 

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Discussion Starter #7
Good stuff, thanks!
How can one figure out case pressure by reading the numbers; higher velocity=higher pressure?
I'll continue to crimp my rounds.
I'm not aware of any way to calculate it from velocity. I'm just going from the assumption that faster rounds = more pressure built up from *something*. My concern was to not approach velocities that would push the envelope, but simply to see if there were variables that led to differences in velocities.
 

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Good stuff. Seems like with faster burning powders such as TG you end up with a lot less Standard Deviation with the crimp.
 

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tagged for reloading reference
 

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Discussion Starter #10
The one thing that's always...intrigued me, I suppose, about this data is that crimping didn't have much apparent effect on velocity, but it did on standard deviation.

I would have thought one might get higher velocity from a crimp. The lower dispersion makes sense, but why dispersion would decline but velocity not change much at all is a mystery.
 
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