I'm not one to run to the vet for every little thing... so I would personally say he will be okay. Little pellets can be passed easily, and it sounds like they are, so I wouldn't be overly concerned.
My dads JRT has swallowed everything
She eats water balloons in the summer... we always keep them up but she always manages to find one or two. She also eats my little brother's bullet-things for his air soft gun. She got x-rayed a few weeks ago because we were concerned about the balloons but nothing was there... she always passed them and we would find them in her stool.
Ugh, dogs!
Mention your concern to your vet, but I am sure it will be fine!