NASA has a lot of smart people working for them. Considering this, I would have expected the Asteroid Redirect Mission to use more advanced technology than a firearm, but alas, sometimes violence is the answer.
Honeybee Robotics Ltd. has deployed a video of their concept shotgun that could be used to push an asteroid into Lunar orbit. Ideas on this aside (I personally don’t like the idea of an Asteroid hurtling anywhere near our planet), the concept is a fascinating look at a real potential “space gun”
Description from Video:
NASA’s Asteroid Redirect Mission (ARM) will capture a large boulder from the surface of an asteroid and transport it to a cislunar orbit. One of the mission risks relates to the unknown geotechnical properties and strength of the asteroid regolith and boulder, respectively.
The Shotgun system reduces this risk by firing small projectiles (“balls”) at the surface of the asteroid or boulder. If a ball impacts regolith, it will create a crater whose size is a function of regolith strength and density. If a ball impacts a coherent boulder, it will bounce back at a certain speed, whose value is proportional to rock strength. If the rebound speed cannot be measured, hollow balls packed with retroreflectors (similar to paintballs) could be used instead. The shell of such balls can be designed to crack open and release retroreflectors when impacting rock above the threshold strength required for successful boulder retrieval.