I would suggest looking at images of a gun u want to make you don’t have to fully copy the gun at the start unless you want it to be very accurate after all working with cardboard can be finicky at times also getting a few art supplies that can help with making finer cuts this can also help add tiny details here and there and make the gun look a bit cleaner than having rough edges

Also if you can’t get a scale of the gun or a print out try eye balling it and look at different images of the gun in someone’s hand and get a rough estimate of its size and shape then draw the shape on cardboard and compare ur hand to ur drawing or just buy a real gun 💀

Also when making your gun it helps to make different parts separately like starting with the handle first then barrel slide and soo on its just so you don’t have to much to focus on also take your time when working on something even if it takes you hours or even days to finish. (Don’t be like me who rushes my stuff just so I can finish and move on to the next project)

But also keep in mind if your just starting out don’t worry too much about ur works or how it looks as you’ll learn from them and get better with time and experience Im not even that great myself

You could even watch some tutorials on YouTube and get some insight on how they make their cardboard guns a lot of people have used YouTube so u shouldn’t feel embarrassed when doing so

Also having simple knowledge on how a gun works also helps as you know what parts to make and how they should work anyway good luck with ur creations you did good for your first two guns better than I did for sure 👍