As steel is ultimately sold by the pound, the thicker the steel, the more you are paying for the same target surface area. Therefore, it behooves you use the thinnest steel that will safely and reliably handle your long term shooting needs. Secondly, a discussion of modern commercial steel. It is easily welded, cut, formed, and drilled.
The CQ is a lightweight, hyper velocity design using an aluminum core and pre-stressed jacket. The aluminum core initiates the expansion slightly after contact, pressing back into the pre-stressed jacket and activating a violent, incapacitating energy transfer. The aluminum nose optimizes feeding and provides a barrier blind entry. The pre-stressed jacket separates into petals sized for appropriate penetration based on the specific cartridge. These petals, base, and core are all designed to penetrate no more than 18", transferring a huge amount of energy to the target in a very short timeframe. The energy is there; our goal is to utilize every bit of it and dumping it all on the surface in a non-vital area is not appropriate for a personal defense design.