Velocity of compressed air through pipe

This started out as a thought experiment and then I realized I was stuck in how to figure it out.

If I have an airsoft rifle that uses compressed air in the tank at 3000 psi. It leaves the bottle regulated down to 800 psi. It then goes into a second regulator that reduces the pressure further down to 40 psi. I want to know what the velocity is when the air exits the second regulator. For the purposes of my thought experiment let's say it goes into a .25" diameter tube and vents into the atmosphere.

At the reservoir I think I can assume the temperature is room temp, but after the two regulators I don't where to go and I don't think I can calculate the density without it to use Bernoulli's equation. I think I have too many unknowns?