Took a new to me, slightly used 1894 Marlin (cross bolt safety) in 357 mag to the range today. With several loads from 125gr to 158gr the carbine will shoot groups which string vertically. They don't seem to walk. Two 10 shot 125 gr groups at 100 yrds were approximately 2.5" wide by about 11" tall. Closer in the groups would get smaller but still had the same shape. Even at 25 yrds with irons the group was around 1" by 3". I have a scope on it for load developement. Any suggestions? Thanks

Sound like uneven forend pressure. When I bench test a lever gun I usually put the front bag as close to the action as I can. On it preferably. That usually cures it. Sometimes the magazine cap screw is pushing on the end barrel and that can have a dramatic effect too. For that I take as little off the end of the screw as possible to remove the pressure. Too much and the magazine tube slips out under recoil.