I'd like to recommend a book that has both gunpowder & sorcery in it.
It is not an AD&D book (c. 1966) so the magic system is of course
different. Spells usually take minutes to hours to cast (items can be
activated more quickly).

TOO MANY MAGICIANS, by Randall Garrett has a murder of a master
sorceror at the Triennial Convention of Healers & Sorcerors in London
in 1966 (history went somewhat differently). He's killed in a locked
room ... and even though he had been working on a paper "The Surgical
Incision of Internal Organs Without Breaching the Abdominal Wall" and
another attendee had been working on "A Method of Performing Surgery
Upon Inaccessible Organs", magic seems ruled out because the hotel is
protected by the best privacy spells of the best sorcerors of the
Anglo-French Empire ...
It is a well done mystery, as they check possibilities (including
invisibly coming in through the windows, drugs, etc., etc.). There
are a couple books of short stories in the series.

In that world the laws of magic had been developed systematically so
that The Laying On of Hands (healing) became as reliable as it had
formerly become eratic. The diversion of a lot of mental talent
into magic research apparently slowed the rest of science and
technology somewhat (if a lot of brain power is going to clairvoyance
spells to find lost animals and children, there will be less left for
steam pumps), and apparently a less bloody history than ours. It has
railraods, steamships, hand guns (excellently hand crafted), printing,
gas lights, but horse drawn coaches.

While higher tech than Cerillia by centuries, it is worth reading both
because it is fun, and for ideas of how to handle crimes (committing
without getting caught or trying to solve) in a world where detects
and other magic work.

Oh, the first time that I read it, I had not read enough of Rex Stouts
Nero Wolfe novels to recognise the vast Marquise of London, who never
left home on business, and has a roof full of exotic plants. By the
second time, in addition to more reading, I had gone through one year
of high school French and immediately recognized the Marquise's
assitant named "Bontriumphe". I had not as yet discovered ROFL (that
didn't cross my mental horizons until decades later), but I was
noisier and wobblier than usual on that re-reading.