Is your barrel the same length as the test loads were fired in? The Colt Commando 38 Special is a collector's item, so I appreciate you are concerned to treat it nicely. However, with cast bullets, you can be considerably oversized before it causes pressure issues. For example, a lot of revolvers chambered in 45 Colt have chambers for the old 0.454" bullet diameter, often being around 0.456" or so, but have a 0.451" groove diameter barrel to meet the modern spec. In general, cast bullets are sized to fit the throats of a revolver's chambers for best accuracy, so they can be 0.005" over groove diameter in some of those Colts. But it's also one of the reasons the 45 Colt doesn't have a great accuracy reputation. When you squeeze a bullet down too much, whether it is in a proper sizing die or letting the gun serve as the sizer, it's hard to do that perfectly symmetrically, so groups are bigger than they would be if the throats and bullets were about 0.002" over groove diameter, which is what, IME produces the smallest revolver groups.
I cast and shoot the 148-grain TL bullets as-cast (no sizing) and mine are close to 0.359-0.3595 with the alloy I use, and they group about half the diameter of commercial match ammo in my K-38. I don't think you will have a problem with them. I have one chamber in my gun that won't shoot them well, but its throat is smaller than all the others and apparently, the barrel doesn't appreciate that.
