I see, I can understand your point but for Projectiles Attaching and Detaching isn’t what you want 
(@OORTIZ also gave a nice explanation)
You can simply disable simulation by default so it will stay in place and run the simulation when you’re ready
For now (as I am outside my home) I don’t know if and what should be a good way to keep the location ‘attached’ to something but instead you can add a component representing your Projectile and when you want to finally shoot - spawn your Projectile and immediately after - destroy the component that’s just playing the visual role in your System 