pneumatic shaft coversion customization

say im currious if anyone has info on weather the pneumatic spear shafts are interchangeable between cressi and omer guns? i had a disscusion with one dive shop(and have been searching online on several websites) that claimed that almost all the pneumatics are manufactured by the same tooling shop and are nearly identical and interchangeble. my interest is that i love my omer but have been considering a backup cressi of the same size, and if they are compatible i can use my backup omer shafts on the cressi if need be.

final question is i have also read in a euro spero board about sanding down the loading end(butt end) of the shaft to reduce the diameter slightly and thus increase the power of the gun by decressing the friction of the firing release(and increasing slightly the release momentum, as every bit adds up). How dangerous a modification is this and has anyone tried this?? perhaps this end is only to hold the line clip and has no function in the triggar mechanism.

on another website someone allready sugested that it is possible to remove the shaft with the gun still cocked(not recomeneded as dangerous)
this would sugest to me that the but end shape is not essential to the operation and a smooth or slightly reduced size of butt end might be a possible modification.

any suggestions very appreciated.

"lock into the piston head to hold the shaft" ok, this makes sense, but the amount of locking holding power seems a bit much. if i just seat the shaft into this piston then grab it to pull out, it is very tight and difficult to remove. this amount of pressure to remove from piston seat seems like it would reduce final total release power. perhaps the mounting but end of the shaft could be only so slightly sanded down just to the point of holding in the piston seat but with smoother release.

"be carefull not to over sand"????? is this be carefull or the shaft will be so lose as to fall out when tipped down. or becarefull as something else bad might happen. also is there any inexpensive dry kit mod on the market.