Many years ago I purchased a cheap ($49.00 - come to think of it... it wasn't that cheap back then) scope... a Bushnell Banner 3x-9x variable. I lent it to a friend who returned it later with the complaint that it was a piece of cheap Japanese sxxt (it was made in Japan back then)....he pointed out that it had just "packed it in" while he was zeroing his rifle and demonstrated by turning the power ring which resulted in nasty grating sounds that almost sounded like broken glass...we agreed it must be broken and that it was crap....
Fast forward 20 odd years and I am staring at the scope -- still in the original box figuring it is finally time to turf the scope as it has never been used since....
I figure "what the hell" might as well open it up and see what makes them tick.
Unscrewed the well known screw that "should never be removed" from the power ring....nothing happens although ring turned freely now with no grating.
Unscrewed the ocular/eyepiece... which just kept coming ... until it unscrewed right off! So I guess any nitrogen was now gone (as if!)
The power ring slid right off the back of the tube as well and...voila....there is the angled cam slot that the screw that "should never be removed" travels in. The other end of the screw engages a tube inside the body of the scope...this being the optical carrier for the lense that varies the power....
Now what?? Why the noisy grating etc...
Well several minutes of pondering reveals that the angled slot is too tight for the screw to travel freely in without binding ... and making a grating noise!! Careful use of a piece of thin steel bar enabled me to lever the opening a tiny wee bit and the screw now follows the slot without binding....the power ring now turns quietly and the whole works seems fine...now back together and destined for service on an air rifle .. to see how long it can last...
So how did this problem occur...well apparently my friend neglected to mention that just before the problem started he managed to whack the ocular pretty hard which resulted in the cam slot being pinched together.
Maybe if the screw had been in mid travel of the slot it would not have bound so tight but at either extreme eg 3x or 9x (where he was set while he was zeroing his rifle) it caused the slot to close significantly...and bind the scope.
So what??? Well the scope is functionning again (not sure how well it will work in the field yet) ... BUT a quick look at several exploded drawings of various scopes ... Bushnell, Leupold, Burris, B&L etc shows that all of them utilize a similar approach to construction eg a slot cut into the scope tube to act as a cam...these slots typically encircle 180 degrees (or more) of the tube... and you want to be careful not to whack the eyepiece hard on a rock or tree trunk if you don't want the problem this cheapy had....admittedly some tubes are stronger and maybe even better fortified in this area... but something to watch out for....fwiw
Fast forward 20 odd years and I am staring at the scope -- still in the original box figuring it is finally time to turf the scope as it has never been used since....
I figure "what the hell" might as well open it up and see what makes them tick.
Unscrewed the well known screw that "should never be removed" from the power ring....nothing happens although ring turned freely now with no grating.
Unscrewed the ocular/eyepiece... which just kept coming ... until it unscrewed right off! So I guess any nitrogen was now gone (as if!)
The power ring slid right off the back of the tube as well and...voila....there is the angled cam slot that the screw that "should never be removed" travels in. The other end of the screw engages a tube inside the body of the scope...this being the optical carrier for the lense that varies the power....
Now what?? Why the noisy grating etc...
Well several minutes of pondering reveals that the angled slot is too tight for the screw to travel freely in without binding ... and making a grating noise!! Careful use of a piece of thin steel bar enabled me to lever the opening a tiny wee bit and the screw now follows the slot without binding....the power ring now turns quietly and the whole works seems fine...now back together and destined for service on an air rifle .. to see how long it can last...
So how did this problem occur...well apparently my friend neglected to mention that just before the problem started he managed to whack the ocular pretty hard which resulted in the cam slot being pinched together.
Maybe if the screw had been in mid travel of the slot it would not have bound so tight but at either extreme eg 3x or 9x (where he was set while he was zeroing his rifle) it caused the slot to close significantly...and bind the scope.
So what??? Well the scope is functionning again (not sure how well it will work in the field yet) ... BUT a quick look at several exploded drawings of various scopes ... Bushnell, Leupold, Burris, B&L etc shows that all of them utilize a similar approach to construction eg a slot cut into the scope tube to act as a cam...these slots typically encircle 180 degrees (or more) of the tube... and you want to be careful not to whack the eyepiece hard on a rock or tree trunk if you don't want the problem this cheapy had....admittedly some tubes are stronger and maybe even better fortified in this area... but something to watch out for....fwiw
