Doors and Windows - installing Shlage lockset

I put in an F series Schlage with levers. The kit comes with a metal drum that serves as a shell and the components slide thru it. I tseems to be some kind of protector for the whole works.
I found the holes were not quite big enough to facilitate
an easy install and I tried grinding them bigger. Most other door knobs dont seem to have them. So I left the drum off and installed without it.
The face plate still wouldnt go in the whole way but it was close. Anyone else run into this problem??
What do you think of these drums?

Normal hole size for a modern lockset is 2 1/8". Older locksets may have been 1 7/8-2.0". To propely center the hole to redrill for 2 1/8, you need to make a guide. Drill a 2 1/8 hole in a piece of plywood, 3/4 stock or similar. Center it on the old hold and clamp, then drill the new hole. Yes, you should install all lock parts, it is a package, and you sacrifice security if you don't install all of it.

My brother had the same problem. Thats how he fixed it..

The metal ring you are talking about is for the backset on the door, not the knob itself. The purpose is to provide an option for mounting the backset (latch) in the door without using a face plate. This is used in a door with a mortise for the latch. It's not intended to be used in conjunction with a face plate. There should also be a black plastic ring that holds it in place.

Anyway, if your face plate on the latch doesn't seat fully, you need to deepen the mortise. Use a sharp wood chisel to do this.