Re: 6.5mm keyhole at 500 yds.
Sounds like a normal reaction to me. Anytime a bullets path is altered in any way i.e.: water, tree, bottles, etc. you cause the bullet to loose energy in its flight path causing cavitation. This cavitation is what causes some bullets to tumble through animals and targets after impact rather than passing through unchanged. Depending on the construction of the bullet will also effect the flight of the bullet. An example would be a FMJ vs a SGK. The FMJ is designed to maintain its shape when penetrating an object, whereby a soft point bullet such as the SGK is made to deform. The reason you got a hole in side 1, is due to the fact it was at its optimum performance. Side 2 with the triangle you started seeing the effect of the bullet coming apart or deforming. The target is a result of lost performance of the bullet entering the bottle, losing momentum in the water and penetrating the rear surface and then hitting the tile. That is about as simple a terms as I can hypothesize and use the little bit of knowledge on physics that I can give you. As far as the bottle not exploding, if it is not filled to the very top where pressure will have no where to go, then it will more than likely pass through with no explosion and a couple holes. These are only my thoughts, but pretty sure I'm on track.
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