My M-29 was made in the late '70s . It has never and will never be fired with anything heavier than 280 gr. No need for that. It's seen many silhouette matches and hunting.
Learn about ballistics - you can load hot but the poor ballistic shape means it will slow down fast so all you get for the hot load is recoil and muzzle blast .
Spitting ? about 1980 they changed the forcing cone dimensions --no more spitting.I took mine to S&W and they did it same day service !
More important than velocity for hunting is bullet construction. Use premium bullets . the 225 Barnes is available loaded by Corbon, the Swift A-frame is available from Federal. Speer's
Deep Curl can be had loaded but this is hotter than the other two.Bullet construction makes a big difference !!
Mine is in excellent condition and will stay that way .Get that "how hot can I load it? " idea out of your head !