1) in the international matches i have been to, some of the available shotgun ammo are longer than the 2 5/16 inches that fit on the strippers i use.
2) most of them have a PF much much higher than the 480 floor needed. i have mine loaded to about 540
3) i know the shot pattern of the ammo i have been using for the past 5 years
4) with a lot of no-shoots, being familiar with the shot pattern would probably be a good idea
5) trying out new ammo, checking what fits best on my stripper, patterning it for various distances for the various chokes, checking out the point of impact of the slugs at various distances etc, then ordering a considerable quantity of slugs, birdshot and buckshot would mean i would have to be in the US, at the very least, more than a week before the match
6) including travel, (i live in asia) that would mean i would have to be off work for at least two weeks (a half-month)
7) with my own ammo, i could just go, shoot the match and leave
but i'll give your suggestion a shot (no pun intended). thanks