A few other factors affect blowby in .45 LC. Many of the guns chambered for that cartridge have pretty-much oversized chambers. Second, the thickness of the case walls do vary from manufacturer-to-manufacturer, and so does the hardness of the case. If you are curious enough, measure the water capacity of different brands of brass after one firing. The greater the case capacity, the chances are the walls are thinner, as the outside dimension are pretty standard. The amount of blowby may only occur partially down the case. It is more important (annoying) in rifles, when the case doesn't expand enough, quick enough to allow the powder gas to escape the action. 8.0gr. Unique under a 250 gr cast bullet is pretty much the "standard". You might also try W231/HP38, which is faster-burning, and may expand the case more quickly, albeit it doesn't take up as much room in the case.
Stay well and safe, Pards!