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In what year did Browning replace the plain Invector choke with the Invector Plus model ?

If it was phased in over time, about when did the Citoris get switched ?

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I haven't kept up with different choke configerations since I quit trap shooting about 10 years ago.

IIRC, the Invector Plus first made it's appearence in the BT99 with the back bored barrel.

I might be wrong, but during the time I kept up with it, I don't think the Citories had the Invector Plus tubes. Again, I might be wrong, but I can't remember the Citori being available with the back bored barrels, but they might have been available after I quit reading about trap guns.

The Citori Over/Under trap model might have had Invector Plus tubes. I just can't remember.

I do remember that I purchased an Extra Full Turkey tube for the Plus barrel and used it in my BT 99 for handicap trap.

It would have been around '90 or '91. Federal and Mossberg brought out the 3 1/2" shell and 835 Pump gun in '89 and everyone was quick to follow. Also around this time was when all places in the states were required to go to non-toxic shot for all waterfowl hunting.

I just recently sold a Browning Citori Plus over/under trap Gun.
It was made in 1991 and these may have been the first guns to have the plus chokes. This gun came with all sorts of features that before this were only custom add ons. Adjustable stock, high rib that could be moved up or down to change point of impact,recoil reducer in the stock that moved in and out and worked like a shock absorber on a car. And back bored barrels that being of larger diameter required these different chokes. Browning at the same time also made the choke longer to in theory ease the shot charge in to the choke transition and thus produce better patterns. Soon after all browning twelve gauge guns used these chokes which fitted right in with the use of steel shot. Some other gauges also use them, 20 for sure, not sure on the others. I forgot to add that because the barrels were of larger diameter the chokes also had to be larger in diameter to get the same amount of choke. I also find plus chokes to be a little on the open side, now weather this was done on purpose due to steel shot I can only guess. The only way to really know you choke is to put the pattern on paper. Which we all tend to avoid.

When I wrote the above, I forgot about the Citori Plus over/under trap gun. Yes, it used the Invecter Plus tubes, also.

My BT99 was the BT99 Plus with the adjustable stock, adjustable rib, and back bored barrel, and made in about the same time period your Citori was made, 1991.