Here are pics of the sight I made for my converted Lee Enfield many mango-seasons back. Must get around to blueing it one day! The tube is .340 long and .300 outside diameter. The aperture is .125 diameter, and is counter-bored approximately .180 diameter. When shooting, the peep-sight is 8.5 inches from the eye. The sight radius on this particular rifle is 25 inches.

From the rear:

From the muzzle-end:

I discovered that it is impossible to photograph the peep as seen by the human eye, ie I could not get it to ghost-out on camera. In truth, this sight does not quite ghost-out completely anyway, but retains a thin solid 'wire' circle. It does not occlude any of the target however. It could easily be made slightly smaller, or bored out a little more, but I really like it as is.

The advantage of building something yourself is perfect customer satisfaction!

PS: I just realised while typing this that the camera would need to be set on telephoto, not wide angle, to achieve the ghost effect. I might try again later, when there are a few less golfers on the course...!