Yeah, it definitely is not going all the way back. It should sit back to that protusion on the right side of the receiver.

Have you tried a little persuasion? Some of these rings are tight. Ensure it is square with the receiver and gently tap it with a block of wood. It should slide back another 1/4" or so.

It is completely round, right? The bottom of ring is pretty thin and is easily misshapen. If so, tapping on that area with a punch and hammer while you are sliding it on will reform it.

If all else fails, and you don't want to wait any longer to assemble your rifle, just cut the ring at the very bottom. Slice right through it with a large pair of wire-cutters or a hacksaw. This will allow the ring to expand a little. Once you get the rifle all put together you will never know this has been cut and the handguard will stay on just fine (trust me, I've done it). These rings are plentiful and cheap if memory serves me.

daveboy