I don't have fibre optic front's on my doubles but do on a couple of bolt bigbores. I prefer them but don't know where to get one for my Merkel. My quickest sights are on a S&W 45ACP AirLite. The rear is a rather wide /deep 'V' and the front is red HIVIZ fibre optic. It is totally encapsulated in clear plastic and presents a perfect red dot from the rear. They are about as quick as any sight pair I've ever used and stand up to holster and other use better that a regular front. My Chapuis 9.3x74r had a kinda wierd yellow see thru insert in the REAR sight that was pretty clear and and I had a Heym SR30? straight pull carbine in 35 Whelen that had the absolutely best combination I've ever had on a rifle. The rear was an ERA pedestal with a VERTICAL flourescent yellow rod in the blade from bottom to bottom of notch, the front was a flourescent red . You can't believe how quick they were. Wish I could find one of the rears but have never seen one advertised. They would be quick on a double. Sight picture looked like an 'i' with the bar yellow and the '.' red.