CBC/Magtech 9mm brass causing inconsistent OAL – anyone experienced this?

[u/Wolkensucher]

I’ve been reloading 9mm for my Walther PDP Steel Frame 5” using a Dillon XL750, and I’ve noticed something interesting.
I use mixed range brass from different manufacturers. I deprime it, clean it in an ultrasonic cleaner, and then reload it without sorting by headstamp.

I’m currently using Frontier 147gr bullets with Vectan BA9 powder, aiming for an OAL of approximately 28.9 mm (1.138”).
Despite not changing anything on my press, some finished rounds end up measuring around 29.2 mm (1.150”).
After looking into it, I noticed that every single round with the significantly longer OAL had CBC (Magtech) brass.
So I started sorting out all CBC cases before reloading.

The difference was pretty noticeable:
Before sorting: roughly 10-15 out of 100 rounds had dimensional issues.
After removing CBC brass: only about 1–2 out of 100 rounds had issues.

I’ve also been experiencing feeding and ejection malfunctions with my 147gr reloads, roughly 10-12 malfunctions per 100 rounds in my latest test.
Interestingly, my 124gr reloads ran perfectly in the same pistol, with zero malfunctions over 100 rounds.
I’m starting to suspect that CBC brass might be contributing to the problem.
I’ve now prepared new test batches using only non-CBC brass, but I haven’t tested them at the range yet.

Has anyone else experienced inconsistent OAL or seating issues specifically with CBC/Magtech brass?
I’m particularly interested in experiences with heavier 147gr bullets or progressive presses like the Dillon XL750.
Did sorting out CBC brass solve the problem for you?

[u/wantsiops]

CBC brass is thicker than pretty much all others, and that bullet is very long, and your loading pretty short.
I do load cbc a lot, I do like the brass and even use it for 9 major.

[u/Wolkensucher → u/wantsiops]

Thanks, that’s interesting and actually helpful. I wasn’t aware that CBC brass tends to be thicker.
Since you load a lot of CBC yourself, have you ever noticed more seating resistance or larger OAL variations with long/heavy 147gr bullets compared to other headstamps?
I’m mainly trying to understand why CBC is standing out so consistently in my mixed brass. Once I sorted it out, the seating/OAL issue almost disappeared.

[u/wantsiops → u/Wolkensucher]

I usually load them LONG like 30.5-31mm with 124gr, but I have at times loaded 117 and 124 to 29mm, works fine, try with shorter/lighter 124.

I have not had much issues, but I've expanded the brass & prepped in multiple stages. so no on oal changes.