Reply To: A question so strange it requires explanation
With few exceptions, the bores of firearms and airguns are slightly different. However, they are different enough that it will be difficult to find bullets that fit. For any reasonable accuracy, the bullets must fit the groove diameter of the barrel. (Certain cast bullet designs need to fit both land and grooves.)
Jacketed bullets will not be useable in an airgun for you won’t have the ability to get them started in the rifling. Finding soft lead cast bullets is also going to be a near impossible task for the smaller .177 and .22 calibers.
But, the good news is that there are bullet molds now being made for airgun use. NOE is but one maker that is starting to stock some, and have choices on diameters of the bore (land riding portion) and the driving band (groove riding portion). Thus, with the right alloy of lead and tin, you can get a bullet to fit.
There are a few who have shot cast bullets of this sort in PCPs, but I am not aware of anyone doing it well with a spring gun—yet.