Apex tactical sells a trigger spring kit for the sigma still. I got one for my sd9 and I am far from being a gunsmith and I was able to put it in myself. Just watch over the video a couple times.
I would buy the rail adapter to make it a standard rail then you can put whatever you want on it. Here's the link if you want to check it out. Laserlyte Smith and Wesson Sigma Rail Adapter:Amazon:Sports & Outdoors@@AMEPARAM@@http://ecx.images-amazon.com/images/I/71P6PaJ0PZL.@@AMEPARAM@@71P6PaJ0PZL
Not sure but just a thought I noticed it was failing to feed on the first couple rounds and then it was smooth, maybe bad mag Springs. Not a expert lol just throwing out my thoughts.