Classic British Flight Sim

Hmm The 250 remington has a muzzle velocity of around 4500ft /sec and a stopping power of 1500 ft lbs force (22lr is around 130 ft lbs) Apparently according to wiki The fastest production cartridge in the world!! Hardly just a .22. I'm with Chris that the projectile is too far out of the case for it to have been still live. But you never know, unless it had been pulled out. Could have been still packed with propellant.
Dale

Thanks for the added detail, Dale.
I acknowledged that it was a high-powered .22, but I would still have done what I said. If it was a doubtful 108mm AA round, it would be a different story.
Ever since I switched off last night, I've been thinking that although I expect the round to be dead, the man in the shop was socially irresponsible; he feared that there was a problem, but instead of dealing with it, hid it in a bag and left it for someone else to suffer the consequences if it was unknowingly compacted or heated.