ruger sp101 sometimes "off" sometimes not

[whacko]

OK weird question. Been having a problem with my ruger sp101. It has been hitting low and left with 125 grain and 158 grain loads for the last 5-6 outings at my gun club. I mean tight groups too.......2-3 touching and the other two within an inch but just grouping low and left. Was thinking of sending it back to ruger. My club is an outdoor range under cover. Today.....I went to an indoor range and rented a lane. At 20-25 feet I was DEAD ON! I mean I was in the 9-10 ring on all 5 at 20-25 feet. SO I go from being a bit disappointed with my sp101 to being absolutely confident that my carry gun is dead on balls accurate. What gives? Could the light conditions being outdoors be messing with my sight picture at my gun club vs. shooting indoors with different light conditions be causing me to line up the sights different? Im guessing here but what other explaination could there be for hitting so consistently low and left at my club vs being dead on at an indoor range?