[JCL3]

Although your mileage may vary....

A friend went through famous defense training classes, 1 week of intense training, hundreds of rounds or more spent. I specifically asked him which hand guns and which ammo had problems. He said most all of the down and out guns had been running steel cased ammo. He also said he would never run steel ammo in anything but firearms made for it that have used it for decades(i.e. AK and variants).

[Myrddin]

My wife and I did a 9 hour, 300 rd course. Winchester 115 gr in the 350 rd bucket. I used a P365 in a leather holster. My wife use the S&W 9mm EZ with a thumb safety, leather holster. At the end of the course, I had no malfunctions, but the leather holster was too slow for the time draw/fire test. Kydex would have fixed it. My wife's principal issue was hitting the thumb safety unintentionally leading to a delay in being ready to fire. Remedied that by trading in the thumb safety model for an NTS. Issue resolved. No ammo issues for the two firearms. 300 rds each.

Roll forward a few months with the 365XL. My wife has an early one and it fails to go to battery often...even half-way down the mag. Full mags seem to drag the slide hard against the first round. Same ammo that was used in the defense class.

Steel cased 7.62x39 cycles fine in my old Romanian SKS. I keep it sparkling clean after watching another owner dump a full mag with a single trigger pull. Filthy firing pin protruding from the bolt face fired on bolt closure. I helped him clean it and restored correct operation.