I have an 870 Express, 1100 Magnum, and a BT-99 (pre-BT100 model).
I have a friend with a Wingmaster and a recent BT-99.
The BT-99s are great trap guns, though they're no Ithaca 5E's (drooling over a friend's collection of 60-year-old trap guns that he uses regularly -- those things weare built with the precision and beauty of a Rolls Royce, and the durability of a tank).
But
neither one of us shoots a damn bit better with the BT than with an 870 or 1100.
A trap gun works best if it's heavier and longer than average, and shoots a bit high. It has to fit you in the position where you will shoot high-gun at a target that's pretty much directly in front of you, not overhead. It tends to have a slightly longer LOP than a gun you'd shoot starting from a "low gun" position, all other things being equal (LOP is not a great measurement to compare between types of guns, as trigger position vis-a-vis the wrist and receiver can be VERY different).
IMHO a Wingmaster Classic Trap (current production) or older 870 trap model (various different ones made over the past half century), if it fits you, will shoot as well as a BT-99 does for less money. Lots of trap records have been set with 870s and Model 12s -- generally with custom-fit stocks. The Wingmaster Classic Trap weighs 8 lb.+ and with a 30" barrel has about the same OAL as a break-action with a 34" barrel. Plenty of heft and length for trap.
I wouldn't get a semiauto for trap unless you're really recoil sensitive and have nothing better to do than clean a gun. Pumps require a lot less cleaning, and though break-actions should be cleaned regularly, it's much quicker and easier than with a semi. Shell catchers sort of work, some of the time. If you don't have one (or a good rubber band), expect your neighbor at the range to grumble and not really want you around. Also a PITA if you reload or even just clean up after yourself, as my range requires.
If you have some cash to spend, remember these words when at the used gun shop: Browning Superposed Broadway Trap.
They're not TOO expensive, cheaper than most new Brownings, but REALLY nice and I prefer them.