This is the main body for the PRHI Large Heavy Pistol kit. To assemble a complete Rifle you need to purchase:
LHP Main Body
Gun Grip Sprue (comes with multiple)
The different parts are available separately so you can use the best material for each part. I recommend a Polished Versatile Plastic or Detail Plastic for the main body and Processed Versatile Plastic for the grip.
The PRHI LHP is compatible with the Bandai SHF Figuarts Space Marine from Warhammer 40k, among other action figures with big hands.