They explode "up" simply because that is the path of least resistance. Less about the sun softening the plastic and more about the large block of wood resisting the expansion of gasses.

The FithOps perimeter alarms are great, but I would really love to see you repeat this setup using the perimeter alarm PLUS a 12-ga cartridge adapter, which should eliminate the problem of the shell exploding and no power behind the projectiles. Such adapters are available in rimfire and centerfire for many calibers, as well as a variety of "barrel" lengths, with or without rifling. You could probably lengthen your target range also.

I think we may get a couple of these to use with primer-only poppers. The possibility of use to simulate tripwire-detonated explosives for CQB training purposes is very interesting to me

I believe the solid mass below the shell is more of the reason they split across the top vs. The sun's heating the surface, try putting the shells in a cooler with ice for 30 minutes before testing, wouldn't suggest dry ice though being it may make plastic in shell too brittle

Love the high speed camera shots. Especially the first one, you can see the expansion of the shotgun shell like a balloon popping. As always a pleasure to watch your videos guys. I also like the "World's Cutest Shotgun Shell". :-) Oh was the black powder substitute louder than the smokeless? Kind of hard to tell on video.

I was rewatching this and out of curiosity I was wondering if you say put a board over it like a 2x4 or 2x6 as a over shield to keep the sun off would that still make it legal. Something to keep all that extra sun heat off of it and how much more would it do with that upper part not getting softer. Still love watching your older videos over and sharing them with others.