1968 Commando silencers

I've just bought two British made replacement silencers (the cigar shaped Dominator type) for my 68' Commando.  When I look up into the silencer end I see a washer type plate (baffle I suppose) fixed near the end of the silencer that only has a 12mm diameter hole in it.  The old silencers do not have this restriction and neither do the silencers on my 59' Dominator.  Can some one advise why they are there and should they be taken out totally or drilled out as they seem to be exceedingly restrictive.  Many thanks.

Harry