My now 8 month old didn't start truly napping until just a few weeks ago. She was the mini napper 5-6 times a day all day long! It was harsh since that didn't allow any time for me to do much during the day.
I am not sure there is any way you can make a baby sleep longer or get on a schedule, but I think it kinda evolves naturally.
I just kept at it and one day it just worked. She now takes two, 1 hour long naps, sometimes longer, and still sleep from 6pm to 6am. It is great!
Just hang in there.
One thing I can suggest is make sure the naps are in his room and that it is pretty dark, have white noise going for sure! Either a fan, humidifier or radio stuck on a scratchy station. Also I would be careful about relying on swaddling. My little one never stayed in her swaddle even as a new born, but all my friends have told me horror stories about having to break their little ones from it. At some point they will be too big to swaddle and then they will have to re-learn how to sleep again. So perhaps you can start to put him down un-swaddled during naps to kinda ease him out of it.
In any case, good luck. I hope your little ones finds a rhythm soon :)