Thanks to a lot of hard research, I have determined what the Gaster blaster weapons are based on. They look like a canid skull, and after a lot of research I found the orbital size, rostrum length, Sagittal crest, fangs, sharp elongated jaw muscle anchors, nasal canal, and teeth, and skull width and length and broad jaw bones, all closely match a large domestic dog, grey wolf, or African hunting Dog, shown in the last two pictures. This disproves that it was based on a fox skull, or a skull of a Pomeranian like Toby’s dog form. The thin parts of the jaw, shortness of snout, blunt rounded jaw muscle anchors, and width to length ratio mean it is likely not a grey wolf, the African hunting dog has a skull that fits the most criteria.
Considering the Gaster Blasters are shown as being longer than Sans body, and with their width, I would say size is not to scale or its a matter of perspective, as even the largest canid known, the long extinct Epicyon haydeni had a skull around 34 cm long and had a skull the size of a male lion, still not big enough if you consider Sans over 5 feet tall.
Also, no canid has a skull that splits in half and jaws that separate in the middle and rotate outwards. That uh… That makes this a bit more pointless.
Still, I wish I knew what reference Toby used for the graphic, most likely it was a dog skull of wolf skull and he just depicted it in a style that happened to look like an actual skull of another species.
Another thing worth pointing out, a lot of people draw the Gaster Blasters like a weapon, or a mask for sans, but it’s important to note the larger Gaster blaster image without eyes or nasal canal is called “spr_g-b_npc.png, an unused filed. For those that don’t know how the game works, lots of characters have black face templates and the graphics of the eyes and other features are added on top separately and animated separately, like Muffet’s eyes. This means at one point, the Gaster blaster was an NPC, a thing with more facial expressions and likely planned dialogue. It’s not a weapon, it’s an actual monster. It might not be a blaster weapon named after Gaster who invented it, it could be some form or piece or entity owned by Gaster that Sans obtained. The Gaster follower with a piece of Gaster claims he isn’t afraid because he has a piece of Gaster with him, as if the pieces of Gaster give powers.
Also worth noting: the left eye is the only one that appears when it is using its power. Just. Like. Sans.