Flechette loads look good, but in practice they stink.
The US experimented with them in Vietnam, where it was thought that they would do a better job of penetrating jungle foliage.
In practice it was found that they didn't do all that great a job of penetrating brush, they had extremely limited range given the light weight nature of the individual flechettes, and they had very poor wounding capacity.
Users clamored for their traditional buckshot loads to be reissued, and the flechettes were withdrawn from service as a failure.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.