seac sub xfire quistion

[Meshari]

i have seac sub xfire 115
now i use 2*16 bands ( riffe band with strech factor 3.135 )

the gun is perfect

no recoil at all unlike my t20 millenium which hurt alot

my terrible shaft is imersion sharkfin special shaft
which i guess is 7mm
it is very light so it is penetration is very weak
and can easily be bent and corrected at same time ( i think it is for big game fish )

i asked seac sub on email if i can use 7.1 or 6.75 mm shafts
without any problem with the shaft guide ( like extra friction )
they said they tried only up to 6.5 mm

does anyone know if i can use 7.1 mm( riffe euro )
without affecting accuracy or friction ?