The earliest production Model 8 rifles were apt to slam fire if a round is placed directly into the chamber and then the bolt allowed to slam shut full force by simply disengaging the bolt release.
Not all the time, not every one, but it was a known possibility with them.
They had a free floating firing pin. No spring loaded rebounding feature so once in a while with the right conditions,,bang.
Loaded from the magazine, the first round slam fire issue is not the problem it is as above.
But you can often load the early rifle that way, then eject that round and see the very faint mark on the primer from the bounce back of the tip of the firing pin .
Remington took care of that by making the firing pin a rebounding style with a coil spring surrounding it.
The bolt is slightly different as the firing pin hole is larger in dia in them for the spring and the firing pin is slightly dif in shape also.
All the Model 8 from there forward and all Model 81 production have that spring loaded rebounding style firing pin.
But always point the rifle in a safe direction when chambering a round. Nothing is 100%