When I go to use the table to craft guns and ammo, there are three tabs in the top left corner of the screen, one for the guns, one for attachments and one for ammo. Well, when I try to switch tabs from the gun tab to any other tab, it just gets me out of the crafting screen as if I pressed ESC. So I'm able to make guns but can't make ammo. I tried reinstalling the mod but that made no difference. Anyone know how I can fix the issue?

Check you don't have any additional mods that would conflict. I've never had any report any issue like this before so it's likely your combination of mods that is causing the issue. Try testing it with only the gub mod installed.