(Probably not a) Shotgun Blast To The Face - NASTY

[doc Russia]

I don't know that it was a downward angle. the guy may have been shot while standing.
It may not be an execution, since there is the possibility that ti was a .30 cal or something like that which just happened to hit the guy in the right temple from a distance, but that is statistically unlikely, and the only way to tell is with a good look at the presumed entrancve wound for stippling, or, if contact distance, a stellate laceration pattern.

[Highspeed]

I've seen photos of gunshot wounds in a restricted British Army report on terminal ballistics. The closest to that guy looked like a Malayan Communist who caught a 7.62 round from an L1A1 right in his bonce at close range in the jungle.

But after seeing the insides of my own body during a couple of traumatic episodes I have developed a profound disinterest in looking at photos of the disgusting gloopy shit contained inside human flesh

The 12g flechette round pictures were instructive as well. I was offered a box of those, but I didn't fancy betting my life to 40 year old ammo that spent most of it's life either baking or soaking in tropical heat and humidity. It's not like they were any good for hunting ducks either, unless you want to evaporate them instead of eating them...

[doc Russia]

The chest also looked somewhat flattened to me; which was what made me think it may be a high speed impact.

That said, it does also look like a high velocity large caliber rifle shot as well, just taking into account the total destruction of the maxilla, and the right side of the skull at or proximate to the sutures

I think that the chest looks normal (aside from the blood). Kind of tough to tell from a 2 dimensional image, but certainly no obvious deformities.
If you look at the whole thing, the elbows bend where the elbows are, the wrists bed where the wrists are, the hips bend where the hips are, and there are no bends where there are no joints. With that observation, it makes the whole inconsistent with some sort of high energy trauma which was delivered to the whole of his body.
here is a pic of a guy who leapt to his death from 9 stories onto dirt:

Note: obvious deformities since his right foot is in his pocket. Also note: largely intact cranium (though that is obviously influenced by the surface he impacted on).

[Yogimus]

The swelling of the neck area makes me think of overpressure or a downward impact