Cracked Brass Test Target

Hello,

I have been working on using modern measuring techniques with statistical analysis to answer a few questions about the importance (or non-importance) of what brass life may play in ammunition accuracy. I had some cracked brass run through the test barrel. The cases were cracked to varying degrees and all definitely would not be recommended for use in any reloading or further reloading. However, I thought it might prove interesting to see what results we would get on a target, and whether or not cracked brass would be wildly inaccurate. It wasn't.


Don't misunderstand- I'm not advocating the use of cracked brass, but rather highlighting that should you run into a case during your shooting, you may very well not be able to attribute that case to a poor result on the target. Since it is impossible to predict when brass will crack other than the likely hood going up with additional firings on a case, it is difficult to really say more than what I have here regarding case failures and accuracy issues. If anyone has a good idea about how we could potentially induce a cracked case to fail during shooting- I'm all ears.

Load Details:

4.12 VV N310
CCI LPP
Misc brands of brass, all USA make
Zero 185 JHP

Seating pressures as measured by AMP Press:



Finally, the chrono data from the labradar:

Stats - Average    735.15    fps
Stats - Highest    777.38    fps
Stats - Lowest    637.75    fps
Stats - Ext. Spread    139.63    fps
Stats - Std. Dev    44.46    fps

It would appear that seating pressure may not matter for accuracy; however, more work needs to be done to be able to resolve that issue completely.

Enjoy,
Chase

Interesting. I wonder if the low shots were with brass that had cracks extending below the bullet base, allowing for some pressure blow-by, and therefore lower velocities.

Dave

Great question- I don't know. Some were "minor" cracks, and others were more severe. I should be getting the brass back, so I'll measure them and update this thread with findings.

Here are the muzzle velocities for the 10 shots:

696
777
638
767
735
703
765
739
760
772

-Chase

I infer from your specifying powder charge to the hundredth of a grain that the rest of the load attributes were equal but for the case.

The low 600s fps projectile explains the first low shot? Would POI shift that much? Now what about the 2nd. The 696 isn't an outlier if we consider there's a 703 also but only two projectiles printed low.

On the other side of the brass life, what does the seating force (as the graph that you posted reads it is force not pressure which would have been reported as psi not that it matters too much, just wanted to note that it is different) in new factory brass look like?

In my experience with some cracked (from the factory) Federal Match ammo many years ago, the variance that was observed came from the bullet setting back in the case during either recoil within the mag or during the loading of the round into the chamber.  When I tested in a gun at 50 yards, carefully loading each round individually, I got groups around 1.75 inches CTC.

New brass generally looks something like this:



If you tumble your new brass in NuFinish, it looks something like this:



No idea just yet if that matters, but it does seem to make a difference (at least, visually).

Ed Hall wrote:In my experience with some cracked (from the factory) Federal Match ammo many years ago, the variance that was observed came from the bullet setting back in the case during either recoil within the mag or during the loading of the round into the chamber.  When I tested in a gun at 50 yards, carefully loading each round individually, I got groups around 1.75 inches CTC.

Ed- I got a note back to me about these cases after testing, it is as follows:

"The test with the split cases. Almost all cartridges did not chamber freely. None had to be forced into the chamber; but, thumb pressure was adequate to seat the cartridge fully."

Just mention it as another data point for folks. There wouldn't have been any setback from recoil (these were not in a magazine, but rather his barrel testing fixture) but it is possible that since these cases couldn't take a crimp that some, however minor, force to seat them could have influenced the results.

It's a good call out- thanks!

-Chase

SingleActionAndrew wrote:I infer from your specifying powder charge to the hundredth of a grain that the rest of the load attributes were equal but for the case.

The low 600s fps projectile explains the first low shot? Would POI shift that much? Now what about the 2nd. The 696 isn't an outlier if we consider there's a 703 also but only two projectiles printed low.

That's not quite right- the 4.12 grains I mention is the average powder drop. I include the additional digit to give an idea of how heavy my 4.1 charge is; the scale offers it, so might as well use it. This particular charge is closer to being a true 4.1 instead of 4.15- which probably resolves to 4.2 even though you really aren't quite there yet. SD is .02 for this particular run.

No idea on which strikes were which from what piece of brass. But the aggregate is what's more important here, imo.

-Chase

Picture of brass for those interested: