Clear or bar insert, depends on the shooter.
Each has advantages and disadvantages.
With the bar insert, you have a horizontal bar to visual check if your rifle is upright or canted, and the amount of cant. With the clear insert, you have no visual reference for cant.
The horizontal bar can/will cover other targets if you are shooting a multi-bull target. This can lead to you shooting on the wrong target/bull. I've done it
With the clear insert you can see which target/bull you are aiming at.
- In regulation 10m precision matches, you are shooting at only ONE target, so there is no confusion.
- For sportster, it can get a little confusing as you do have multiple bulls on the target sheet.
- The real confusing target, is when you shoot at something like a 20-bull target in a 4x5 configuration. This is not a regulation target, but is something that can be printed at home on a letter size paper. The more bulls on the sheet, the more confusing it will be.
Clear inserts allow more light to enter the sight and your eye.
AS for aperture size, these are the guidelines that I got and use.
- Size the aperture so that the bull stays INSIDE the aperture most of the time. IOW if you wobble a lot, use a larger aperture than if you don't wobble a lot.
- - And on days that you do wobble more, use a larger aperture. Don't think you have to stick to ONE size.
- Do NOT use an aperture that is so small as to leave a tiny strip of light around the bull. That leads to other issues.
- Testing by various junior groups have shown that using a LARGER aperture generally results in better accuracy. Though it takes a bit of time for the shooter to get used to the new larger aperture.
- If you shoot at different size targets/bulls, or at different distances, you have to change the size of the aperture, to match the apparent size of the target.
Bottom line, is you need to have an assortment of different size inserts, to match to the rifle, target, distance and you.