First of all, you would need to get the position of where your projectile hit the object, then you would use that position to place a part in the correct spot on the wall.
However,
I wouldn’t recommend using unions for bullet holes as it’s going to be really performance heavy and might cause a lot of lag especially with fast shooting weapons. A good alternative to that is to use decal bullet holes which cause a lot less lag compared to creating unions.
I agree with this. Using Decals would be much more efficient for performance than to actually create Unions as bullet holes. Each union you create adds to the rendering time.
I ask you: do you know how I would do so that when I shoot and fall in position the decals are placed in the rotation of the surface that the bullet hits? if you need the script let me know