The key to fitting a moderator correctly is all in the threading
There are six key aspects to the thread:
- The thread MUST finish at the abutment end with a clean thread and not taper out – in practice this means cut on a lathe with a point tool (Not a die-nut) with an slight 1.1-1.7mm undercut at the abutment end
- The thread MUST be parellel to the bore – again in practice this means cut on a lathe with a point tool (Not a die-nut)
- The thread MUST be concentric to the bore – again in practice this means cut on a lathe with a point tool (Not a die-nut)
- The Moderator must be slightly lose on the muzzle thread – in practice just before the mod stops with a nice “clunk” against the abutment the mod should have 2-3mm of “wobble” at the far endIf your moderator is fitted by someone less familiar with the
specifics of moderator threading, they are likely to fit a “nice tight” smooth thread –
unfortunately this results in the moderator aligning with the mod thread/muzzle thread instead of squaring to the abutment face – which is the most accurate - The abutment face MUST be Square to the bore – again in practice this means cut on a lathe
- The thread chosen should leave sufficient material between the root of the thread and the bore, so an 1/2″ UNF thread would have a root diameter of circ 11mm – on a 308 (7.62mm) calibre – this gives a barrel thickness of just ~1.6mm!
And finally
The Back-Bush MUST BE FITTED on moderators where they are supplied/designed for – T8, T4, etc – most reflex (back over the barrel) types