Sigma 50-500mm - Tripod collar problem (?)

[jimlizard]

My brother bought a Sigma 50-500mm, but there seems to be some kind of problem with the tripod ring. After unscrewing the lock mechanism, the ring doesn't rotate. We have to completely remove the head of the screw in order to open the ring and even then, the rotation is not that smooth.
There seems to be some small metalic pieces making contact between the lens and the collar, which are probably creating some kind of lock.

Is it normal on this lens, or do you think those metalic pieces may need some lubrification?

Thanks for your help!

 

[artyman]

Only ever taken the collar off my 150-500 once, it has four lugs that locate in a grooved channel. Loosen the screw and rotate the foot until it lines up with the remove position and it will then lift off. No lubrication on mine. I presume the 50-500 will be similar.

 

[jimlizard]

Thanks for your help, Ken!
I'll see if it works.