i recently purchased a mossberg SSi 1 single shot slug gun and was wondering if anyone out there owned one and what type of slugs they had the best luck with group wise

Welcome to the forums Sharky!

You'll get a better response if you post this in the "shotgunning" forum! <G>

FWIW I have been loading my own slugs, it is really the only thing that has worked for me so far. Copper Solids work good in my mossberg 695 but a better load is Ballistic Products Dangerous Game slugs, over about 34 gr of unique (I believe, don't have my load book handy) With a roll crimp in new shells.