Thanks for the ideas, I never thought of going in and deleting keyframes on a baked simulation. I'll try that and let you know what happens. At any rate, here are the expressions I used. I first made a couple of new attributes, CustomValue, which is a float, I think, and CustomRotation, which is a vector. Tha partice object was renamed to Casing Creation Expression: //Random Value// CasingParticleShape.CustomValue = rand(-10, 10); //Random start rotation for each instance// CasingParticleShape.CustomRotation = <<rand(360), rand(360), rand(360)>>; Runtime Before Dynamics Expression: //Random Rotation Over Time// CasingParticleShape.CustomRotation += CasingParticleShape.CustomValue; //Attempt to stop rotation of instances// if{CasingParticleShape.age >=3) (CasingParticleShape.CustomValue = 0); The idea of the if statement is that at around 3 seconds of age, roughly when a shell casing lands and bounces once, it stops rotating becase the number that gets added to the rotation value from the previous frame is 0. So, now that's my current set-up. Will try your suggestions. Rage. If you or anyone have any more ideas, I'm all ears. Thanks