Murphy's toy has been around at least one major Magical slugfest, so I would think it is safe in the hands of a wizard. The way I see it, is if his .44 doesn't cook off all six rounds at once, shoved in his pocket during the throw-down with
Cowl during the Darkhollow
(DB spoiler), then a 30 round mag is just as unlikely. That little party had to have more mojo in the air than anything to this point in the series. It would not be a matter of quantity in this case, but of complexity. The self-contained cartridge is not complex: just container (casing), cap (bullet), powder, and the cap, which happens to produce a very small explosion when subjected to enough
physical force/pressure.
The way my mind works, assumes that the murphionic field works like EM fields, EM radiation, or particle radiation. If you expose one or fifty forks to the same level of radiation the solitary fork will have the the same level of radiation as one of the fifty. When Harry walks into a room with a single light bulb it sometimes goes out. That does not mean that if he walks into a room with 500 light bulbs every one always go out. He has been in enough public places that I think my theory holds water. Magic has to obey the laws of physics, as Harry would say. I could be wrong about the rules as Jim sees them--after all I am not him, but this is the conclusion I've come to (keeping in mind all of the tech failures we've seen {that I can remember} have had an electromagnetic component to them).
I think iPhone incendiary is taking it a bit too far. IMHO I think an iPhone would just smoke and become your new paper weight.
Mine has gotten uncomfortable to the touch on long flights (when watching a movie), but I was kind of making a point without meaning literally bursting into flames. I tend to forget that my typing lacks inflection sometimes.
[EDIT here down] Ok, going back to usefulness I do not think a two handed firearm would be
practical to a wizard during a fight. You got to have a hand ready to throw around energy or bring up your defenses. As far as Harry's reluctance to pick up an automatic, I think that is just Harry being paranoid, but "just because you're paranoid doesn't mean there isn't an invisable deamon about to eat your face."
Going back to an earlier post, I could see and possibly accept someone enchanting a bullet (projectile only) much the same way Harry uses his silver rings. That would be some hefty work to throw away, unless the enchantment is attached to another simple item which is designed to pass on the enchantment to other items through a less involved method before charging. Runes of sigils on the barrel would act as a release trigger, much the same way Harry triggers his rings--he doesn't have to be uber-precise on impact time. This method does seem like a kind of copout.
Thinking about it, if you want your 30 round cap .22LR to pack as much punch as a .729 Jongmans with Hydro-shok, of course (a 110lb rifle with "brutal" recoil), you better work your butt off on 30 enchantments, strap them on your shoes (think 1980's 'Roos shoes), and go run a marathon or three.
