There is a huge difference between closed and open muzzle as regards recoil. Closed muzzles with screw-in bands tend to go up in the moment of firing causing inaccurate shots. Eventually the mind gets used to it and fixes the errors of the gun, but according to physics open muzzle should be more accurate.
I agree on the extra power part too. It is due to the extra piece of rubber passing through the hole.
Here is some info on the recoil and on closed vs. open muzzles
http://www.dapiran.it/dapiran/tecnic...tm#TERZA_PARTE
Sorry if you don't speak Italian, but the article has some very good graphics, so you can get the idea. There are loads of other sources also in Italian, but I think Dapiran is good enough expert, so I choose to trust him
