One can't help being sarcastic, when it comes to the anti-gun lobby, and what they're prepared to do, including stifling education.
It is rare to see anything in collegiate books, now, concerning gun design. The one in mention is one of a very few, and at that, it only mentions the one formula. I have several books on all the ME disciplines, by several authors, but that is about the only one left, that mentions firearms. OSU has a good tech library, though, with many old books that do mention it.
When studying mechanical engineering, one learns the basics, but to design guns is a field that advanced training would be required in, I would think. Especially military ordnance. I don't know if the firearms manufacturers have internal training for the new EITs or not. My guess, would be a hiring those who attend gunsmithing colleges, then go on to study ME. That, or hire from schools in Belgium.
One of the better books that I've read for study, was by Rhienmetall, on the design of guns and ordnance. Another, though old, is by WW Greener.