The hangfires in the Jeffery sound like they were possibly underloaded (they were mentioned as being reloads). Large cases with too much unoccupied space can do this - I had these dramas with reduced cast loads in my 458. There is also a risk of pressure excursions if this happens with a slow burning powder. The pressure wave bounces up and down the case and adds to itself at the ends and can put "rings" in the steel of the chamber or possibly even blow apart the rifle (haven't heard of local cases of the latter though). This pressure increase effect is well known in the gas industry and is known as "pressure piling", and there are standard measures generally employed to prevent it occurring.

I also found out a bit more about the CZ Custom Magnum model. The difference from the standard Safari Magnum are – they have a barrel band sling mount, #1 Fancy Grade (?) American Walnut timber and are glass-bedded. The Jeffery and Gibbs also have mercury recoil reducers fitted. This equates to the extra $1,500, or thereabouts, that they cost over the standard magnum.

I was interested in the Jeffery as it is lower in power than the Gibbs. A 500NE would meet the requirements for BGR group 3 and the Jeffery is next closest for a bolt gun.