Rival round adapter for XSHOT or NERF gun barrels

This is my first model and is a Rival round to any barrel that fits it adapter. I would love for feedback and things I could do to make it better. (That includes criticism which I am hoping to be mostly constructive.)  Made in TinkerCAD and I am hoping to release more (better) models soon. IMPORTANT: It is better used on more powerful guns and even then, it should be more like a grenade launcher than like shooting a regular dart. In the photo is an Xshot Excel Kickback which doesn't launch too well and is mainly for showcasing purposes. It does not fit all barrels, and some may need to be held against or taped to the barrel, so it doesn't slide out and for a better seal. We all have different experiences, so what worked for me may not work for you. I hope that it will be somewhat useful and fun.