I have 5 and 2 developed leaks from the base. Opened them up and tried some PTFE, did the trick for a wee while. Don’t suppose anyone knows the right size or slightly larger o-ring to replace the original or if it a case of going the way of MP7 mags and using instant gasket?
I’ve used an HAO rail on both my 10.5” and 14.6”, also on my long 416, really good quality, very well made and not as expensive
on my 10.5” barrel Mk16 I used the 9.3” HAO rail (sorry about crap quality pic)