I used the Sawzall on some tubing that was already welded in place. Didn't work at all. Was using DeWalt 18T bimetal blades. Tooth the teeth off faster than I could change the blades. That's why I was asking about the holesaw. I might have attacked the tubing with too fast a rate of speed, like you mentioned. Will try some practice cuts with some 24T blades.
I got involved in some upgrades to a homebuilt cage a number of years ago, was supposed to be 4130 and had been certified as such, and it was an older car then. The tubing in that car was unbelievably hard and I had the same issue. Was terrible to work on. Don't know what it was, but it wasn't Cond "N" 4130.
