I shoot a BT-99 straight stock (fixed I/M choke)through the winter and switch back to my BT-100 (M/C non-adjustable stock, fixed full choke) during the Spring. I've shot both guns (the 99 for 30 years and the 100 for about 10 years) and would not sell either one as I like both. I do find the biggest difference is as I got in my 50's (age, not my singles score) it's easier to shoot the higher rib as on the 100. On the BT-99 you're looking down through the barrel to pickup the target guickly. The 100 makes that job much easier. Even though the 100 has a drop out trigger, the 99 has such a dependable hammer & trigger system that I've only had to take it apart once in the past 30 years to put in new hammer spring inside. However, I have broken a firing pin in the 100 and you have to take the stock off to replace it. I've never heard of a firing pin breaking in a 99. If it ever does, it's removed from the block without removing the stock. Both great guns. BT-100dc