I've got the same issue and why I've gone to a scope. It's almost seems like a caterac in the center of the eye but my eye doctor does not see one. I noticed that this issue of the target in the center of the front  aperture disappearing occurs when my eyes get tired. I have not experimented how to prevent this during a match. I'd be very much interested too in hearing from others that have this issue and may have found a solution.

I have a cataract/astigmitism corrective lense implant ,,,,and the same thing will happen to me if I go to small on the rear aperture for the given light conditions.  Might try playin around (read, go larger) on the rear aperture and see what happens.

Cary

I have shot iron sight matches without an aperture, just using the globe. Not exactly accurate  Two times I have discovered fixes that have been too temporary to be of any real benefit 

We had so many guys giving up iron sights at Tacoma, I quit scoring an aggregate.   Left the iron matches for  the few that wanted to shoot them. 

Edit: the issues do not affect anything but iron sights and spotting 22 holes at 200 yds.  Nothing can be done but make it worse.

Rek,

I have experienced the very same problem, and have found some things that have helped me.

Most important, the closer that I can get the rear aperture to my eye (safely, of course) the less I see that small dark central area. I am using Montana Vintage Arms tang sights on many of my single shot and lever rifles.  Having the rear sight on the tang has been a great help.  With some of my rifles, I kind of cheat forward on the stock to get closer to the sight.

I also like the Hadley discs with a variety of aperture sizes. I have bought several, but it's easy to have just one Hadley and move it from one rifle to another.  The MVA Hadley discs are a very nice unit, and they have an O-ring inlet around the rear rim of the sight to prevent it from scratching the stock when folded - a nice touch that isn't on one of my Hadleys from another mfg.

Receiver sights are difficult for me to use because of the central dark spot, but if I use the right size aperture, the sight picture is liveable. I guess that I should try to use one of my Hadleys on one of my receiver-sighted leverguns.

Finally, I was overdue for an eye exam, so earlier this year when I visited my optometrist, I asked her to set me up with an extra pair of glasses, non-bifocal, that were corrected for about 34" in front of my eye.  I had earlier had a similar pair optimized for computer, and that, and a suggestion from a friend, gave me the idea to ask for these glasses.  It's a bit of a pain at the range to switch back and forth between two pairs of glasses - perhaps I should have had them made as bifocals with my reading prescription at the bottom.  Next time I will.

I hope that some of this may be of some help to you, good luck!

Edit: Oops - just read Joe S's post and definitely agree.  If the rifle's receiver has a flat top, I use a plastic carpenter's square to make sure that my sight's staff is perpendicular to the bore.  This handy way of adjusting the angle of the staff was passed on to me by a wise and respected levergunner.

Quote:
This is called 'the fuzzies' in the ocular because the vernier is not mounted perpendicular to a barrel that is not 100% horizontal
* First insure the foresight insert is mounted to the middle of the bore
* Put rifle in a padded vice and put a bubble level on the flat of the barrel to hold the rifle in a horizontal position
* Put a vertical bubble level on the staff so it is 100% vertical
* Look through the ocular to insure there is no 'fuzzies'
* Put a laser bore sighter in the bore and shim or file the base of the vernier to the tip of the pinhead/post or middle of the circle insert on the foresight with the vernier still in a vertical position.
* Looking through the ocular if the laser is not on the tip of the pinhead/post or center of the insert - the foresight is not exactly in the middle of the bore
Results: vernier accurately positioned to the foresight and no more "fuzzies"
Excluding the laser bore sighter, I use a magnetic 6" torpedo level for horizontal alignment and the Wheeler small bubble levels for the barrel
(You need to Login or Register to view media files and links)
(You need to Login or Register to view media files and links)

All my rifles with verniers are the graduated MOA staff mid and long range graduation ones.  I hate Marbles type peep sights and refuse to use them

A 1/4 of a bubble move to the left on the vernier will compensate for approximately 4 MOA windage at 1000yds
Didn't mention this because not many folks shoot 1000yds

Quote:

I found letting the bubble touch the line was perfect to get to 10000 yards without losing all my windage to bullet drift.  

Back in the day when I could see irons, the minor affects of elevating from 200 to 1,000 did not matter. What did matter was turning 45