As Far-Trader requested, here are a few 'air' rifles to add to Traveller.
1. Low tech air rifle. This first appears at TL3, and is a contemporary of the flintlock. While expensive and difficult to manufacture, the air rifle is by far the most deadly weapon on the battlefield. Whereas the common infantry weapon is the single shot, smooth bore musket, and can be fired 3 time per minute by trained troops, accuracy is nonexistant and it requires massed volleys at as little as 50 meters to produce even small numbers of casualties.
The rifle musket does exist, but it is difficult to load, with projectiles that often have to be hammered down the barrel.
By contrast, the air rifle can fire rifled ball projectiles massing some 12g at 250m/s one after another from a 12 shot magazine. The air resevoir contains enough pressure for several dozen shots, and can be replaced with a charged one fairly rapidly.
And unlike their blackpowder contemporaries, the air rifle emits no cloud of smoke and makes comparatively little noise.
Repeating air rifle. TL3. Length 1.2 meters, mass. 4kg, cost (at TL3) Cr750
Armor Matrix
NON JCK MSH CLH RFL ABL CBT
+1 +1 -1 -3 +1 -1 -5
Range Matrix
CLS SHT MED LNG VLG
-4 +1 -2 -5 no
Damage: 2D
Note: This rifle can be fired every round. A normal flintlock musket can be fired every third (6 second) round by a skilled musketeer, or every fourth turn by an average musketeer.
A rifle musket can be fired every 10 (6 second) round.
1. Low tech air rifle. This first appears at TL3, and is a contemporary of the flintlock. While expensive and difficult to manufacture, the air rifle is by far the most deadly weapon on the battlefield. Whereas the common infantry weapon is the single shot, smooth bore musket, and can be fired 3 time per minute by trained troops, accuracy is nonexistant and it requires massed volleys at as little as 50 meters to produce even small numbers of casualties.
The rifle musket does exist, but it is difficult to load, with projectiles that often have to be hammered down the barrel.
By contrast, the air rifle can fire rifled ball projectiles massing some 12g at 250m/s one after another from a 12 shot magazine. The air resevoir contains enough pressure for several dozen shots, and can be replaced with a charged one fairly rapidly.
And unlike their blackpowder contemporaries, the air rifle emits no cloud of smoke and makes comparatively little noise.

Repeating air rifle. TL3. Length 1.2 meters, mass. 4kg, cost (at TL3) Cr750
Armor Matrix
NON JCK MSH CLH RFL ABL CBT
+1 +1 -1 -3 +1 -1 -5
Range Matrix
CLS SHT MED LNG VLG
-4 +1 -2 -5 no
Damage: 2D
Note: This rifle can be fired every round. A normal flintlock musket can be fired every third (6 second) round by a skilled musketeer, or every fourth turn by an average musketeer.
A rifle musket can be fired every 10 (6 second) round.