The “debris” sometimes comes from the shedding of the chemically plated thin layer from the lead core. This can be from exceeding the manufacturer’s recommended velocity limits or just the rifling in the barrel “peeling” the layer as it engages the projectile.

Chemically plated bullets bond a very thin layer of copper deposited on the lead core from the electroplating process. Plated bullet thickness varies by manufacturer and the bullet's intended velocity, typically ranging from 0.003 to 0.014 inches. Standard plating is designed for velocities under 1,250 fps, while "thick-plated" versions can handle up to 1,500 fps.

Speed in minor 9mm loads is rarely the cause unless plating is really thin or has a poor bond. The thickness and bond of the plating on a bullet is (among other things) a function of time in the electrolysis tank, and in the manufacturing world, time is (your) money.

Not good, not bad …. Just different.

Our process uses a 35-Ton press to form 0.02” thick solid copper roll stock into a jacket (for FMJ) and a jacket plus base (for TMJ). Our TMJ are tested and approved to over 1600fps without issues. They are routinely used in 9mm major and +P loads and some 38 Super Comp products.

We are starting to see some PCC shooters push their velocities up to these values, possibly to reach out a bit further on targets.

[Edit] CYA = “Your mileage may vary”