Re: any 338 Federal loaders out there
Though I have given the chambering some thought, my view is that if I were going to go for a larger diameter bullet on the .308's case capacity, I wouldn't employ half measures. I'd go whole hog and work with the .358 Win. For subsonics, I'd be looking at heavier nominally .38cal and 9mm pistol bullets; because IMHO, a subsonic is simply a pistol round built on a rifle case. ...Or more properly, I'd be playing pretty exclusively with .44Mag/SPC carbines. No need to get more specialized than that.
Greg