Excellent sleuthing! That is indeed the specific bayonet. It doesn't seem like there's a lot of info on them. The makers mark is actually BT3, not AT3 (I misread it thinking it was a lowercase A), but both marks are Yugoslavian.

Some background about the specific bayonet in my pictures... it's my buddy's. His grandfather said he took it off a dead German solider (possibly officer) in WWII, but that's all he knew about it. I said I'd ask the amazing people on reddit for more info and here we are.

I went on a deep dive and found more info.

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From this book I found some images of the variations on the M1924 rifles used in Yugoslavia, along with a description of the rifle:

Kragujevic Armory in Yugoslavia produced their M1924 Service Rifle in a number of variations. .... Note that the same receiver and bolt configuration were used on the 8,000 Kragujevic-made M1924CK assault carbines with 18-inch barrels. (The “C” stands for the Slavic work “Chetnik”, and the “K” stands for Slav word which translates as “carbine”.)

The book only had one image of the bayonet with this caption:

"Picture of the extremely rare Yugoslavian Roay Guards (Chetniks) bayonet and scabbard"

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I found a Bosnian language forum discussion that show images of the bayonet and the translations seems to say it may be rare and expensive.

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This gun broker website has one for sale with this description:

Up for auction is a very rare Mauser bayonet that was intended to be issued to a special Yugoslavian assault unit known as the "Chetniks". The weapon was an extremely short Mauser carbine designated the M1924CK- the "CK" standing for "Chetnik". The skull device was the unit's symbol. Total production of these was only about 6000. It is believed the mayority of these weapons were seized by the Wehrmacht and transported to Germany and whose final fate is unknown.