Maybe this has been done before, but I just wanted to explore the idea.
So, I thought about a rifle round specially designed to defeat kevlar armor at short ranges. It would have the exact dimensions as a 5.56 Nato, just have some of the lead replaced with aluminium to increase the speed of the round.
Inside is still a lead core with a corundum tip used as a penetrator. If you ask why I chose corundum, it's because it is hard as shit and cheaper than diamonds.
The lead core should push the corundum tip through the armor, while the aluminium is shaved off.
The following MS Paint pictures are not 100% representing of the actual insides of the round, they're just an approximation.
1. This is the original design, the lead clump at the back would give the penetrator better characteristics, since as opposed to the other two designs the lead core has the diameter of the corundum tip. Though this placement would most likely lead to a very unstable round that could sway around if hit by a strong gust of wind.
2. The same, just with the clump placed further towards the tip. This has better flight characteristics, but extremely decreased penetration.
3. The frontal lead weight is sloped to slightly increase penetration as oposed to model 2, while maintaining the improved flight characteristics of said round.
The biggest problem with 2 and 3 are that the tip would most likely detatch from the core, which would be left outside the armor with the aluminium, basically negating the principle on which this idea is based, though this can be solved by making the lead weight and the core two seperate components. This in turn increases production complexity, a t6hing that should be kept at a minimum.
The biggest problems are that the tip will shatter if the target is too hard and that the bullet will quickly loose speed over short distances.
I'm no expert, this is just a stupid idea by some random on the internet, so don't expect too much. Your input is apprechiated.