Standard pressure is 100 kPa or 14.504 psi. (This is the pressure for "standard conditions" on Earth. Typically what we experience.)
SAAMI Pressure for 9mm +P is 265,450 kPa or 38,500 psi.
So the difference between the inside of the barrel and the outside is 265,550 kPa or 38,514.504 psi in a perfect vacuum of space.
The gun will barely feel the difference. In fact there is more variation in that with typical inaccuracies of powder volume in most rounds.
The round is completely sealed before and during the firing from atmospheric oxygen, so all combustion will happen the same way with one possible problem: Temperature.
Temperature in space is around 2.725 Kelvin. This is around -270 C or -455 F. So without solar radiation, the firearm will be cold enough to potentially not allow the primer to ignite the powder. Also, there may be low temperature metallurgy issues that cause problems at that low of a temperature. There will more than likely be issue with polymer parts.
My Glock MAY Kaboom, in a non-humor sense. It would be the grip failing, even if the barrel and slide did not fatigue. I have not looked at the temperature range of the polymer that Glock or others use for the plastic pistols.
Now, lets get to another problem. How much do you lubricate your gun before you go into space? You did use dry lubrication so the grease and oil isn't frozen, right? -455 F is COLD. Otherwise, you will get a jam after the first shot, because the slide isn't going anywhere.
Anyhow, that's all I got. Because of the temperature issue, my answer has to be a probably or most likely.
I vote NO. Because it would be kinda hard for you to get your booger hook on the bang switch with those huge gloves you have to wear in space, however, were it not for that insignificant fact I believe the gun would fire based on some of what I've read in this thread.
The military test small arms to -40F. They run into problems even at those temps. Low temp reliability is the reason that Comm Block ammo is still loaded with corrosive primers, BTW. The military also see chamber pressures and velocities drop off at low temps. In space the temperature is approaching -454F. If the primers are beginning to have ignition issues at -40F, they will completely dead long before reaching -454F.You make good points, li'l brother.
My intuition tells me that the low temp probably won't prevent the combustion of the propellant. If the primer can make a spark, that should be enough energy to initiate the reaction and once it starts, it's going to finish.
Whether or not the primer will ignite and make that spark could be the stickier of the two wickets. I would bet that it will, though.
How much energy is necessary to activate the primer compound and is it temperate-dependent?
The thing is, there's virtually no convection or conduction in outer space. There are no molecules to bump into an object and transfer heat. We are left with only radiation as a form of heat transfer. Objects in a virtual vacuum cool down very slowly, if I remember my physics from nearly 30 years ago right. Objects that start warm will stay warm for a long time in space. This is why it takes asteroids millions upon millions of years to cool down, and you end up with Windmanstatten Patterns in them.
Plus, if the gun is exposed to the sun, it will likely get very hot, and maybe just cook off on its own.
Again, if I remember my HS physics right.
Which is questionable.
Radiation heat transfer is proportional to temperatures ^ 4th power. The heat from a room temp gun is going to radiate at a high rate to space, unless the sun is shining on it (as you mentioned). Then you'd have to consider the net rate of heat transfer (whether it's into or out of the gun). It would depend.
Heat Capacity of Steel (Cp) is around 0.5 kJ/kg K So it takes 0.5 kJ radiation to reduce 1 kg of steel by 1 K (or 1 Celcius).
Not sure of the weight of a Glock slide. Say 2.2 pounds? -> 1 kg.
Yes it will, the bullet will go straighter and faster also.