Rick:
How to tell the interrupted thread type locking-
Pull the bolt out of the rifle and look at the lugs, if there are one on each side, its OK
If there looks like about five smaller lugs on each side, it is the "Thread" type.
Ammo, Bertram Brass Co ( Australia) makes the brass, loading dies will be hard to find, but a custom maker like 4-D Co. in Mt Vernon OH will fix you up at reasonable cost.
Load data, you are on your own with this one, Cartriges of the World lists three loads using modern powders.
The 280 was one of the first "high intensity" sporting rounds but nothing too wild by todays standards.
Factory ammo got 2900 fps with 140 grain bullets and 2700 with a 160 grain.
Regular 7 mm slugs are the proper size if you intend to load for it.
If the thought of the bolt being closed but not locked makes you nervous, try this.
After putting the bolt back in, get a steel cleaning rod that will fit down the bore, pass the rod down the barrel and against the face of the bolt. Push on the rod *hard* if the bolt is incorrectly assembled you will be able to push it open with the cleaning rod
Jim
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Lay up some blackpowder and flints
The rest we can build, if need be