If they were available, they didn't come in suitable pellet sizes, performed poorly and were limited to 12-gauge.

Like birdshot, buckshot is described by pellet size, with larger numbers indicating smaller shot.

This is an excellent video shows you different pellet sizes, all the way from bird shot up to a single one-ounce bullet:

Phoenix 2000 is sold in 500gm packs at £3.30 for the general pondfish recipe and £3.70 for the special Koi formula - two pellet sizes, large (8mm) and small (4.5mm).

In the early days of steel shot, such doubts had some basis in fact, primarily because such shells either weren't available in large enough pellet sizes or the loads were too light.

It can handle steel shot, but there are no adequate steel goose loads, the largest pellet size in 20-gauge being No. 2.

The next pellet size beyond FF is No. 4 buckshot (.24).

Although most modern shotguns can handle steel shot, problems have arisen with some, particularly when the pellet size goes above BB.

The cylindrical pellets then undergo a grinding process to achieve a uniform pellet size.

The newer CANFLEX bundle has 43 tubes, with two pellet sizes (so the power rating can be increased without melting the hottest pellets).