My suggestion is to practice, but not in the way you think.
The issue isn't that you're squinting vs keeping your eyes open like you think it is. The real issue is that when you're squinting, what you're doing is slowing down, taking time to find a good sight picture, and then pulling the trigger.
What you need to learn to be a good competition shooter is how far away and how fast you can make accurate hits, and adjust your shooting on the fly as you go.
Take another look at the diagram of the stage posted above, with some lovely MS Paint work added to it by me:
If I'm in the red position shooting at the left side target, the time and care I take aiming is going to be dramatically different than the time and care I take to shoot at the close target at the green dot position.
What you should do is set up some USPSA or IDPA targets at 3 yards, 7 yards, 15 yards...some distance like that and force yourself to shoot under time pressure (a timer is a great tool for this) for Zeros or Double Alphas. Do it to the point of failure at each distance. For me, a very close target takes basically zero effort and almost no sight picture to be a good hit. If there is a target at 3 yards, I'm pulling the trigger twice as fast as I can as soon as I see even a hint of the front sight post...because that's all the aiming I need to do to make the hits at that distance. The further the distance to a target, the more care I take in making sure I have good sight alignment and a good trigger press....because that's what I need to make hits at distance. I need to be standing still and get a great sight picture to hit the A zone on a target at 20 yards consistantly. At 3 yards? I can run by it, barely see the front sight and slap the trigger and I'll hit alphas.
Just because I was already playing around in Paint: We all know what a good sight picture looks like....something similar to the sight silhouette in the middle. But if I see any of the four bad sight pictures on the left and I'm aiming at a close target? I'm pulling the trigger on it. Why? because the Alpha zone on a USPSA target (and the Zero on an IDPA) is pretty darn big if its up close. You don't have to bullseye the thing...you just have to get it in the red box. That's easy on close targets, and hard on far targets.
All of the handgun competition stuff is about balancing speed and accuracy. A big thing that square, static range shooters simply don't know when they start is what ranges they're capable of making quick hits on the move, and what ranges they need to slow down and take their time. That can only be learned by experience...either at matches if you're willing to learn the slow way, or on the range on your own time if you want to get better quicker.
The issue isn't that you're squinting vs keeping your eyes open like you think it is. The real issue is that when you're squinting, what you're doing is slowing down, taking time to find a good sight picture, and then pulling the trigger.
What you need to learn to be a good competition shooter is how far away and how fast you can make accurate hits, and adjust your shooting on the fly as you go.
Take another look at the diagram of the stage posted above, with some lovely MS Paint work added to it by me:
If I'm in the red position shooting at the left side target, the time and care I take aiming is going to be dramatically different than the time and care I take to shoot at the close target at the green dot position.
What you should do is set up some USPSA or IDPA targets at 3 yards, 7 yards, 15 yards...some distance like that and force yourself to shoot under time pressure (a timer is a great tool for this) for Zeros or Double Alphas. Do it to the point of failure at each distance. For me, a very close target takes basically zero effort and almost no sight picture to be a good hit. If there is a target at 3 yards, I'm pulling the trigger twice as fast as I can as soon as I see even a hint of the front sight post...because that's all the aiming I need to do to make the hits at that distance. The further the distance to a target, the more care I take in making sure I have good sight alignment and a good trigger press....because that's what I need to make hits at distance. I need to be standing still and get a great sight picture to hit the A zone on a target at 20 yards consistantly. At 3 yards? I can run by it, barely see the front sight and slap the trigger and I'll hit alphas.
Just because I was already playing around in Paint: We all know what a good sight picture looks like....something similar to the sight silhouette in the middle. But if I see any of the four bad sight pictures on the left and I'm aiming at a close target? I'm pulling the trigger on it. Why? because the Alpha zone on a USPSA target (and the Zero on an IDPA) is pretty darn big if its up close. You don't have to bullseye the thing...you just have to get it in the red box. That's easy on close targets, and hard on far targets.
All of the handgun competition stuff is about balancing speed and accuracy. A big thing that square, static range shooters simply don't know when they start is what ranges they're capable of making quick hits on the move, and what ranges they need to slow down and take their time. That can only be learned by experience...either at matches if you're willing to learn the slow way, or on the range on your own time if you want to get better quicker.
