.223 rounds have a lead core, yes. Every one of them I’ve ever shot or seen is fully jacketed. I’ve shot .223 through 1/4” steel plates at the range. Close range I confess. But a small round, jacketed, with a high velocity can penetrate steel. I guess it just depends on thickness etc etc.
I was under the impression that a stray bullet had hit the hydraulic line?
That was my assumption also.
Edit: X OP mentioned "Leak is opposite the shooter cylinder is steel, bullet is lead." - so maybe not possible?
You fail to consider physics.
.223 rounds have a lead core, yes. Every one of them I’ve ever shot or seen is fully jacketed. I’ve shot .223 through 1/4” steel plates at the range. Close range I confess. But a small round, jacketed, with a high velocity can penetrate steel. I guess it just depends on thickness etc etc.