Just add some weight in the stock bolt hole. The reducers available that slide in the stock work mostly on weight and counter action systems like Mercury and springs. Just by adding some weight to the gun it will reduce alot of felt recoil. Also add this with lighter loads. Also as important is gun fit.
An easy home built stock weight is cut a small length of copper pipe and sweat an end cap on one end. Melt a desired amount of lead into the pipe. After it has cooled wrap black electricians tape around the pipe so its a snug fit in the stock bolt hole. Instant recoil reduction. It will change the balance of the gun. Add a little at a time checking how the gun feels each interval. Always easier to add more than subtract when too much.
I had a Slick Slide put on my wife's BT 99, with adjustable recoil pad and adjustable comb, the comb & recoil pad are attached so the gun moves unde it. She loves it and the price was reasonable. Work was done professionaly and I had the stock back in about 2 weeks.
Carey Barron put a slick slide on my BT99 stock and has a LOP of 14 inches with a 1 inch recoil pad. With a thinner pad, the LOP can be reduced to 13.5 inches easily. The whole setup works beautifully for me with no felt recoil at all even with heavy loads. Suggest you give him call. JM
Thank you for all the replies. We started in this sport late October with field guns. She was the first to get a true trap gun and I just got mine (a 99 also) Now's she's "dropped the gauntlet" and it's a coin flip who's outshooting who right now. She is shooting Remington STS or Winchester AA, Claybuster Windjammer, International Clays 18.5 Gr., 1 1/8 oz #8, Cheddite primer. It is the same load I shoot and I love the pattern and she refuses to shoot less. She feels it will put her at a competitive disadvantage. Due to her comb configuration, there is 1" of stock between the end of the comb and the adjustable butt pad. It is a gel type butt pad 1" thick. It seems the slick slide is the way to go however, I believe it would be less expensive to sell her gun as is and find one already done. I'm thinking I'm looking at +- $300 to get this done.