An interesting pair of articles on this site: https://neillgilhooley.com/engineering/military/

I can't understand the purpose of the Burney design. Assuming it worked properly you'd still end up with a rifle that would be far more powerful than an the average infantry man would need. It might make a good sniping round but rifle design itself doesn't appear to be one that is conducive to accuracy.

The Hall rifle looks much more promising except for that ejection system!