Now the air guns are spec'd and handed out to each team.....
https://sports.yahoo.com/pit-guns-issued-nascar-190010631.html
–A lottery system will determine how the guns randomly are issued before the race (this is similar to how NASCAR distributes its restrictor plates for race at Daytona International Speedway). The guns will be returned within an hour after the race.
–Pit crews will be limited in modifying the pit guns. The socket can’t be removed, but there are some adjustments allowed with grip tape and screws. Certain parts of the gun will be sealed to detect tampering.
–Air pressures for the guns will be mandated by NASCAR, and the pressure relief valve will be set by a digital gauge.
–Teams will be provided with three guns that are labeled as front, rear and spare.
–The guns will be tested regularly to ensure their consistency.