I'm hoping this will be a simple question, but the subject has always somehow bothered me a bit. We see all sorts of Gelatin tests on Youtube, and some even appear to be relevant and valid, but are gel tests without denim, or other barriers even valid? There are a lot of videos shot either way, or even both ways, and except for uniform comparison the non-barrier tests strike me as unrealistic, especially in light of the effect denim and other light barriers have on bullet performance. A great example is SIGs 124 gr 9mm bullet which expands well in bare gelatin, but plugs up and falls on its face with denim. So, how valid are bare gelatin tests?