I have also shot verticly strung groups at 100yds. Is your ML scoped? I use a peep and I figured that my vertical stringing was shooter error. I am happy to keep a 2" MOA @ 100yds with a peep. If my ML was scoped I would expect better grouping. At 150yds, I hold a 3" MOA but I have never strung a vertical group at 150yds. They are a bit more random. This is all off a bench. Off hand I shoot a 4"-5" MOA @ 100yds. I am happy with that. With shooting sticks the grouping shrinks a little but not much. At 150yds I can keep it on a paper plate off hand and with shooting sticks. I use 110gr of BH209 and a Barnes 290gr TMZ out of a T/C Omega. I have read that the 209 primers could seperate the sabot from the powder upon ignition before all the powder has burned and that is sposed to give you inconsistant groups. I have read that there is breech plug that has been adapted for a .22 Hornet cartridge and that is sposed to help with flyers but I havent tried or seen it first hand. I guess if your ML is scoped I would expect a better group at 150yds and it could be your load or shooting style. More trigger time fixes just about any problem.