Educated guess (plus some optimisation)...
function reload()
{
var a; for (a=0; a < bullets; a+=1)
{
bul_panel[a] = pan_create(NULL, 101); // Create this bullet-panel in runtime
bul_panel[a].bmap = hud_bullet; // bmap_create("frame.pcx");
bul_panel[a].size_x = hud_bullet.width; // <<< Important addition
bul_panel[a].size_y = hud_bullet.height; // <<< Important addition
bul_panel[a].pos_x = 366 - 7*a; // Position it in "clip"
set(bul_panel[a], SHOW); // display "this" bullet-panel
wait(1);
}
}
Your panels are being created with a width & height of 0 by 0.
The above code should fix that.