Stuff you know if you have an ARYou lovingly reload precision crafted rounds one by one.
Stuff you know if you have a Mosin Nagant
You dig your ammo out of a farmer's field in Ukraine and it works just fine.
Stuff you know if you have an AR
Your rifle's accessories are eight times more valuable than your rifle.
Stuff you know if you have a Mosin Nagant
Your rifle's accessory is a small tin can with a funny lid, but it's buried under an apartment building somewhere in Budapest.