“I looked for years, and never found any 16 gauge shotgun shells for my Remington.”
16 gauge is making a comeback.
L
You probably don't live in the south. While not popular, every ammo store has a box or two. When ammo mania hit years ago, 16 gauge was about the only thing left on the shelf. I talked to a clerk at a gun shop. He told me that they sell just enough 16 gauge to make it worth their costs. But you are going to get full hunting shells- not the cheap target loads.
In the 60s, where I grew up, the 16 gauge was more popular than the 20 gauge.