Some dead people leave their children money, or a house. Or they leave their kids nothing and leave everything to the family cat. Well, the Major's dad left behind two hunting shotguns. Not just the kind of shotgun you walk into Wal-Mart and buy, but antique shotguns manufactured by famed gun-maker E. J. Churchill. They're worth around "a hundred thousand pounds" (1.15) if sold as a pair. Not as much if sold apart.
Not that it matters: the Major would never dream of selling them. When Bertie, his brother, dies, the Major wants the guns reunited. He wants to keep them together as a family heirloom, to… to what? He can't pass them on to Roger when he dies, because Roger will sell them. Bertie's daughter, Jemina, wants to sell them, too. This is galling to the Major. He values tradition more than money, and he sees these guns as family history.
It's a history he wants to keep, maintain, and nurture. He has a ritual of cleaning the gun which is quite sensual. "He dipped his fingers in the hot oil and began to rub it slowly into the burled walnut root of the gun stock. The wood became silk under his fingertips" (1.38). Bertie did not feel the same way. His gun is neglected, compared to the Major's. "They looked nothing like a pair. His own gun looked fat and polished. It almost breathed as it lay on the slab" (8.13). The Major's gun is still alive, while Bertie's is dead, just like Bertie.
The guns, though, end up being kind of a red herring. The Major lends Roger his gun, anyway, and takes Bertie's to rescue Abdul Wahid from the knitting-needle-wielding maniac (we are not making this up). In a freak accident, the gun goes off, shoots the Major, and both fall over the cliff. The Major is saved, but the gun washes away.
Even though the Major spent most of the book fighting over and fretting over this gun, he doesn't take the loss that hard at all. For one thing, it's not his gun, anyway. Having the two guns together won't reunite his family or bring his brother back. He can't rewrite history. So the Major stops focusing on the gun, and devotes his attention to Mrs. Ali and his future.