Hi there, sounds like his arms and limbs are starting to get stronger. Two things you can do, either wean him off the swaddle one arm at a time, or if he seems to really like it (if it ain't broke, theory) then make a larger swaddle blanket by cutting a twin sheet in half. My spirited son, Brendan, needed the swaddling, and I swaddled him up until 6 months, and I made a larger blanket.
Hope this helps!