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Tony, the main differences between the rifle scope you remember and a modern telescope is mainly in the size of the optics (diameter) and the amount of magnification.
Modern scopes with large diameter mirrors have to be collimated much more precisely than small scopes, as the allowed error for light coming from the edge of the mirror is much less than light near the centre, and the larger the diameter the smaller the allowable error.
It's likely that an 8" reflector is about 50x more critical in it's tolerances than the small scopes like those used on rifles. If you don't get the collimation spot on with the large mirrors then you see a blurry mess.
Typically the reflected image from the primary has to end up within a few mm of the exact centre of your focusser, and this is hard to do with low cost scopes and have it stay there as you point to different parts of the sky. Many people recollimate as a matter of course when they move the scope a large amount since that's just the easiest solution.
cheers, Bird
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