Early BSA Aperture sight Question

[muffett.2008]

Checked out your problem, there were over 5 million No.9's made, (so they reckon) the original was designed for the early L.L.E's, then came the bracket shortly after, I think that you have a binding problem with the sight mount hole, a couple of my No.9's have a similar problem.
Attachment 41092
This can be eased with an oversize drill to create a very slight chamfer in the back of the sight mount hole. Once the sight can sit flat, the spring tension will not create the bind. Or you can use a shim washer.

You will find that with the sight on a No.1 Mk.III, the sight will need to be in the raised position to sit flat, if mounted to an earlier model without the side mounted safety, the sight just lays naturally.
Attachment 41093Attachment 41094
.............and a few of the sight brackets of the time.Attachment 41095