.357-.358 lead bullets will work fine in .38 S&W for most purposes. Larger diameter bullets (.360-.361) are preferred but are far from essential. Some reloading manuals specify .358 bullets. Actually, SAAMI spec for .38 S&W lead bullet diameter goes down to .355". Look it up. Some like using hollow base wadcutter bullets seated about halfway into the case as they expand under pressure to fill the bore. But if all you can find are .357-.358, use them and don't worry about it. My favorite .38 S&W load uses 125 grain truncated cone .358 lead bullets. I once pulled bullets from some very old .38 S&W dud cartridges. They measured .357".