i think masterp has a great idea, that could be it. check that spring guide.
also, consider ammo. some have had jamming probs with some of the cheapo ammo (i think pmi is one that was a concern).
i have heard of some 581 that have just had jamming probs. some have had to be sent back. it seems there may have been a bad run with 581 somewhere along the line. i hope yours isn't in this category.
check the spring & try different ammo. and i assume you are using factory mags? hopefully it is just something easy. my mini has about 900 rounds with only one jam so far.....