Howdy Jeffly,
Due to differences in overall length,some rifles have trouble feeding the .38s. This seems to not only dependent on the type of rifle,but the particular rifle being used. The only way to tell for sure is to just try some .38s in your rifle and see if they feed. If they don't,a good gunsmith should be able to adjust the gun so it will feed both .357s and .38s.
Bellicose Bill