These cordura straps don't really stretch out all too much. Best option would be to order springbars of varying styles / middle widths. This should take up the slack or add slack depending on which type you choose.
Omegas come with 1.78mm width springbars, so you could either try 1.5mm to loosen or 2.0mm to tighten. Also, curved springbars will even further loosen the fit but will introduce a bit more of a gap between the case and the strap.
Although it's destructive drilling a small hole between the two works pretty well as the rubber insert is very tough, and once mounted in the clasp it won't really move around much. The leather also works, but not quite as well since the pin holes don't have the rubber surround.
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