TargetTalk

Firing a Steyr evo 10 in 55 deg. F environment. Fired 18 rounds fine, the 19th round sounded different and hit low, the next round stuck in the barrel. The cylinder was very cold to the touch and showed 75 bar of pressure. Anyone experience this?

The low pressure and cold cylinder says you have a leak somewhere. To cool the cylinder that much, it would have had to have been pretty abrupt. I'm surprised you didn't hear it unless you were on a range with other people shooting firearms and had ear protection on.

I shoot my Evo in that temperature frequently.
75 bar is still in full velocity mode.
There is something else wrong. Maybe a regulator issue.