I'm talking at least -5.00 or so (I am -7.25). I have an issue which has been bothering me. I zero'ed and qualified on the M16 wearing BCG's (huge, ugly glasses for those that don't know) in basic and had no problems. A few years later while preparing to deploy, while wearing my civilian hi-index (thinner lens, normal looking glasses) glasses, I could not get a decent zero group after spending two whole days on the range. I still qualified however. I shot again in-country wearing the modern issued glasses (also hi-index I believe) and still could not get a group despite being able to qualify.
That was when I noticed images get very slightly distored through my glasses if I'm not looking directly down the center of the lens (i.e. looking at the target through the sight mounted on the weapon with my cheek against the stock). Does anyone else have the same problem? Do you think the distortion is enough to make my groups inconsistent on the 25m zero target? I'm curious if my glasses are the crux of my problem, or if the issue is with me, not the glasses.
I think I understand what you are saying/asking. I have heard this solution, Have a set of glasses that the prescription is put in upside down or the lens turned over.
You are tilting your head forward which causes you to look through the top of the lens where there is no prescription thus you are getting no help from the glasses. By flipping the lens over you can tilt forward and line up your eye with the prescription.
I think you can test this with a simple head tilt backwards and aiming. It will be uncomfortable.
Sorry it took so long for me to find this thread and reply. I have gone through a lot of the same problems, and here is where I'm at currently.
First, I am very nearsighted with a bad astigmatism. -7.00 spherical with a -3.25 cylinder correction at 180 degrees.
I also wear bifocals (I'm almost 57 years old), and for my daily wear glasses I wear progressive bifocal lenses. (Formerly, up until about 18 months ago, I wore gas-permeable contact lenses with very good results. However I developed an allergy to all of the solutions, so can no longer wear them - had to go back to glasses full time.)
First, the progressive lenses are useless for rifle shooting. In various positions, mainly sitting and in prone, you are looking either through a portion of the lens where the prescription is not right for the distance, or are looking over the top of the glasses frame with no prescription at all.
Keep in mind that with my degree of myopia, I am not only unable to focus on the front sight, I can't even SEE the front sight without my glasses.
First I purchased a pair of "tactical" safety glasses made by Wiley-X with a separate prescription insert that snaps in between the outer safety lens and the eye. These wprked pretty good, but I had lots of problems with fogging of the lenses. I think having two lenses stacked so close to each other diminished the airflow around the lenses, aggravated by the fact that my exhalations seemed to deflect off of the stock and go right up between the lenses.
I finally found these Bob Jones Shooting Glasses
. They offer several features that worked well for me. First, and their primary useful feature, is that one can adjust the frame so as to place the aiming lens high and to the left (for a right-handed shooter) of the aiming eye. This means that, when in position over the rifle with a consistent cheek weld, either in offhand, sitting, or prone, ones aiming eye is looking more through the center of the lens. Their second useful feature is that the lens is perfectly round. This means that, if one is afflicted with a bad astigmatism as am I, you can simply loosen the clamping screw and rotate the lens slightly to align the angle of the astigmatism correction with the angle needed by your eye at that time. Also they are actually inexpensive, at less than $100 delivered.
This is important because, as I learned much to my surprise, ones axis of astigmatism can change from day to day and even from hour to hour, depending on such things as how rested one is at the time, ones degree of hydration, the amount of cheek pressure one is putting on the stock, etc. (Did you ever have one of those days when, say, driving to work in the morning, you say to yourself "I just cant seem to see right today"? That's why. You astigmatism axis is a little different that day from the axis ground into your lens.)
When I ordered my glasses, Bob Jones remarked that mine have the strongest correction he ever tried to make. Also, Bob recommended having the prescription put into only the aiming lens, and making the left lens a plain planar lens with no prescription at all. I was a little skeptical abut this, but he was right! By having no prescription in my non-aiming lens, I can keep that eye open and get no interference with the sight picture I get through my aiming eye - it's like wearing a blinder over my non-aiming eye. Of course this is due to the needed strength of my prescription and may not hold for everyone. Even so, the glasses have worked out great for me. I went from not being able to resolve a 12" aiming black at 200 yards - at least not well enough to use a decent 6:00 hold - to be able to actually get a decent sight picture at that range. Quite frankly, these glasses are the difference between being able to shoot NRA Service Rifle, and not.
I can't say enough good things about them.