I like the beginning of this manga, but everything after this chapter goes downhill in my opinion. I agree with kanaloa that he should've gone for a more "logical" weapon. How does he know how to make a gun in the first place? How did he know how to make it work with magic? He most likely doesn't have any experience in making guns. Another gripe is how fast everything goes later, it skips so much, I want the character to struggle, to suffer, he just blasts away his problems.