Smokeless powder also " explodes", just at a lower rate, depending on the "blend".
BP actually "burns" at a given rate, I don't know, offhand what it is, maybe 25,000 feet per second.
GENERALLY, it will produce something in the range of 10 to 15,000 psi. It CAN however go to well over a 100,000 psi.
Smokeless powders are pretty potent, too. It is mandatory that you follow reloading data to load ammo. You may load as much as 20 grs of Unique or 2400 in a 44 mag case 9 grs or so of Red Dot in the same case, same gun, and get at least as high velocity, more kick, from the faster burn, almost an "explosion", and uncomforably high pressures.
The powders that produce the highest velocities and the lowest pressures are progressive burning powders, they don't "detonate" in the chamber or the case, they continue burning and building pressure all the way up the barrel.
A short barrel will blow out unburned smokeless powder, too.
Smoke is not unburned BP, it is water vapor from the Potassium Nitrate.
Sulfur is not the corrosive, it is the Chlorates left in the Potassium Nitrate when it is made into BP. Purer KNO3 has less Chloride in it, makes for a less corrosive BP.
BP is not bad, depending on whose it is.
A 100 years ago or more, the "cowboys" fired their BPs and rinsed them in the "crick". They either dried from the heat of the sun or they greased them with the bacon grease from breakfast, lunch and dinner. They ate a lotta fatty foods and don't seem to have died from all that many heart attacks.
Cheers,
George