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You are right, for constant pulling off the film from the roll, the biggest tension may occure towards the end. But this also depends on how the friction is designed! With a primitive constant friction, the faster turning reel causes more resistance, and the force to the film will rise.
But: only when the machine accepts bigger reels, it needs a more friction, in order to avoid free running of the full reel. For 50 ft, nearly no friction is needed.
When watching the reel movement of a sprocketless Projector (I once had a Bauer T182, with no upper sprocket), you note, that the upper reel is swining periodically: first it is pulled by the claw (really accellerating the complete weight of it) and it starts rolling, until it stops again, waiting for the next pulling impulse. It never rolls continuously. And with each pullin, the film in the upper film channel gets in tension and touches the film chanel or some plastic spring - and the projected image is "breathing" more than usual.
Excuse me, but this MUST be more force to the whole film (and claw), than an continuous linear sprocket pulling.
The camera design (Kodak 200 ft and Beaulieu 200 ft) also got back to sprocket again, as the sprocket, as an mechanical interface between linear movement and intermediate movement, holds anything away from the registration section what could mechanincally disturb.
So, the registration of both 200 ft solutions is considered to be better as that of the 50 ft cardriges. At least concerning the Beaulieu cardrige I can tell you that it is so.
Well, I keep my projector always in the best maintained state that is possible. The only danger related to sprockets during normal projection (not in threading mode) is, if a sprocket goes loosen and turns at a wrong speed, applying tension to the film. Or if the spring that holds the perforation to the sprocket teeth, goes off. But both situations are rather theoretical. THe biggest problem is the auto threading mechanism and a dirty gate, pinch roller or sound head presser.
Besides, most quality projectors are sound projectors, and I have never seen a totally sprocketless sound projector.
The only sprocketless projectors I know are toy projectors and the latest Bauer models ot the dieing amateur film area, where the upper sprocket only had been rationalized away. And this projectors are well known for a bad registration.
And yes, I PERSONALLY have seen these models for sale in normal ware houses and at photo dealers, before all the nice toys went over to the second hand sections of the shops.
Pedro