[poacher]

Open muzzle -more power? maybe a little if spear is hitting closed muzzle due to some bending may have a little friction? testeing 2 different guns with different rubbers is not an accurate comparison of muzzle styles you would need exactly the same gun with only the muzzle different to be conclusive and then try over a number of shots and swap rubbers one rubber may have more elasticity than another from same manufacturere due to age,manufacturing variation and many other variables. closed muzzle faster to load ? I find open easier to get spear into mech without having to thread it through the small ring at end of muzzle just drop it on to barrel and push back last 50mm or 2" single wrap of line is almost automatic without concious effort after some practice your hand swings line around pin and end of gun then slide back to hook on line release in one fluid movement unless its tangled which happens also with closed muzzle, I have both but prefer open muzzle -only problem is in dumping surf it may come loose and line come off . this is not very common except in breaking surf.
Peter