[spaghetti]

Open muzzle just gives you a cleaner aiming line, cause you have a visual perception of the shaft in all its length with no interruption. For this reason, some people say that open muzzles give guns a higher accuracy. Is it true? bah...Me I think it's just a fashion thing: newest guns are almost all with open muzzle, and this is why they are more expensive (new models have higher prices than "outfashioned" ones).
Me I've always used closed muzzles and feel no problem with accuracy. On the contrary, closed muzzle guns are faster and easier to load: unlike open muzzles, they dont' require to wrap up the shaft with the line.
--bulk rubber: you buy rubbers and cut them in the required size, instead of buying them ready made. It's a thing you can do to create your own custom circular bands, making a do-it-yourself wishbone with knots of dyneema or kevlar line. This way you save some bucks...