9mm: How hot does the temperature on a cars floor heater gets?
Not hot enough to burn your ankles to the point you would need medical attention...which is a lot less than the engineered operating temperature of your weapon after it's fired a few rounds. When you are shooting at the range, you don't worry about the remaining rounds in your semi-auto magazine or revolver cylinder. This, despite the fact that the weapon acts as a heat sink for the temperatures generated by rounds already fired. The weapon is designed to function normally despite being very hot. A lot hotter than your car heater could ever make it.
In other words...no problem.
9mm: I wonder because, (a) if I ankle carry in winter, and I have my heater on full blast heat at max speed on my ankle near my gun can this damage the ammo? (b) from extream heat in my car to cold air when I hop out.
(a) No.
(b) No. In fact, the opposite is true. The actual threat is rust-forming condensation caused by introducing a frozen weapon
back into a heated environment. Your walking around all day in freezing temps will cause condensation to form on the weapon when you climb into a warm car or heated building. A deeply frozen piece of metal (your firearm) will wind up covered in frost (like an air conditioner coil) from the water vapor present in the warm automobile atmosphere. This frost will then melt (as the weapon warms up), remaining as liquid on the metal of the gun. This could potentially cause rust if you fail to wipe the weapon down and apply oil. In practical terms, this means checking your weapon once or twice daily (wait until it approaches room temperature, disassemble, wipe down with a dry rag, and apply a light coat of gun oil).
A few minutes stroll from a parking garage to a restaurant in cold weather is not going to compromise your firearm. However, spending all day hunting in sub-zero weather, then returning to a heated cabin will cause the rust problem I described.
Hundreds of thousands of law enforcement folks in this country get in and out of autos every day during extreme winter temps (with the heaters running). They do this while keeping their issue handguns secure in retention duty holsters. They don't have any problems as long as they do a modicum of maintenance (90% of which is simply checking the weapon at the end of the day to see if there
is any moisture or rust).
9mm: (a) Can this cause primes to go bad faster? (b) I might just remove the gun and place it in the center console when driving.
(a) No.
(b) Always an option if it makes you more comfortable, but nothing you
need to do.
Now...can you run into problems at
extremely low temps? Yes. Some lubes can congeal at sub-zero temperatures. Metal parts can start to become brittle at extreme levels of cold. For instance, it's a bad idea to expect a military weapon to function when you have been standing out all day in -50 degree F and decide to do a rapid magazine dump or go cyclic with a belt of ammo. Best to slow fire a few rounds to bring the weapon up to normal operating temperature, allowing the heat generated by firing to permeate the weapon's moving parts. BTDT. But for civilian CCW ankle carry of a pistol...not really an issue.
Think about this:
Weapons (inanimate objects made of metal and plastic) are capable of functioning across a much wider temperature range than the meat puppets who carry them. The atmospheric temperatures required to cause malfunction of a firearm or its ammo (heat or cold) are also temperatures that would kill you long before the gun ever demonstrated a problem. 
Hope this helps...
