ฟันธงครับ
1. ปืนสามารถยิงได้ปกติเพราะดินปืนมีตัว oxidizer อยู่แล้วจึงไม่จำเป็นที่ต้องใช้ออกซิเจนจากสภาพแวดล้อมภายนอก (ดินปืนพกออกซิเจนมาเอง)
2. การยิงในอวกาศกระสุนจะประสิทธิภาพสูงสุดเพราะจะยิงไปไกลเท่าไหร่ก็ได้เพราะไม่มีแรงโน้มถ่วงเป็นตัวต้าน
3. เสียงไม่สามารถเดินทางผ่านสภาวะสูญญากาศได้ (แต่อย่าเหมาว่าอากาศคือออกซิเจนอย่างเดียวนะครับเพราะอากาศประกอบไปด้วยกาซหลายชนิดเช่น CO2, O2, etc.) ดังนั้นถ้าไปยิงในดาวอังคารก็อาจจะได้ยินเสียงก็ได้แต่เบาๆ
Gun fire in spaceSteve Williams asked the question of whether a firearm would fire and function in outer space without the presence of oxygen gas. The answer is yes. Gun powder is a mixture of a fuel and and a oxidizer. Ammunition dose not require any oxygen from the environment to burn. As a matter of fact, ammunition made for military purposes is sealed for water proofing. There is no way that oxygen can enter the sealed cartridge. Fireworks, TNT, and the solid fuel mixture used in rockets will also work because of the same reason.
A machine gun or self-loading gun would operate just the same. These types of firearms are operated by the recoil of the shot or by venting some of the expanding gas in the barrel to a cylinder linked to an operating rod. Other guns will also will work in outer space. A spring operated BB gun and a CO2 pellet gun would work just fine in the absence of air. The only gun that would not work is a manual pump-up pellet gun. This gun must draw in air to be compressed in a cylinder to drive the pellet.
If a typical firearm were to be shot in outer space the performance would be much greater than one fired on earth. In the absence of air there would be no resistance to slow the bullet down. The bullet would strike the target at any range at the same speed it left the barrel. In the absence of gravity the bullet's path would be a straight line at any distance. There is also one more difference. In outer space the gun would not make any sound because there is no air to conduct the energy of the muzzle blast.
http://www.madsci.org/posts/archives/jan99/915630015.Ot.r.htmlSound does not travel in vacuumBecause sound is the vibration of matter, it does not travel through a vacuum or in outer space. When you see movies or TV shows about battles in outer space, you should only be able to see an explosion but not hear it. The sounds are added for dramatic effect.
http://www.school-for-champions.com/science/sound.htm