WiseWolf made a great .308 chamber flag model that was simple and very effective. 

I like the model so much that I custom sized it in 2 other calibers as well. This model contains flags sized for:

• 308
• 22
• 223 (I know, not very different than the 22, but I decided to custom make it to fit even better. Print if you want) 

Credit to WiseWolf since this is mostly just a resizing remix. Original: https://makerworld.com/en/models/21719#profileId-19849

Enjoy & be safe everyone!