Still no idea what I am doing wrong here..

Yesterday I threw in a bit of scrap and it came out looking alright.
This problem is only happening with my tumbled parts...






Just found someone on eBay UK selling the Craftsman Electric Powder Coat Spray Gun that is quite popular over in the US for its low price.
So for £40 with powder I thought I might give it a go.

https://www.ebay.co.uk/itm/NEW-Craft...72.m2749.l2649