Interesting gas trap

[RT Ellis]

Sub-caliber guns are used differently from spoting rifles. The sub-caliber ammunition is usually similar in ballistic performance to the main gun ammunition, and used to train sighting and adjustment exercises, the sub-caliber rounds being allot less expensive than main gun rounds. Usually no main gun rounds are fired until after the crew has been sufficiently trained that firing main gun ammunition is justified. The ideal sub-caliber device is a barrel that actually fits into the barrel as was the rifle M1903A2, however another standard weapon mounted as in this image was an inexpensive way to provide gunnery training.

I've seen M16 5.56mm rifles mounted on the 105mm main gun on M48A5 tanks, and plastic targets about 2 inches wide, used for gunnery sighting exercises.