50 feet of 8mm at 24 fps is about 167 seconds or 2 min. 47 seconds, which is approximately equal to 100 feet of 16mm at 24 fps. It is virtually impossible to ascertain the frame rate in a viewer. Most older 8mm projectors are variable speed which is useful for determining the frame rate. Only use a projector which is known to be clean and in top notch running condition with film known to be in good, non-shrunken condition under close supervision.
Some projectors have a capstan rather than a sprocket drive, which is easier on film.
If the reel if full to overflowing, add an additional 50 feet and be very careful in handling to avoid spilling the film.