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keep an eye on on NZpost tracking (once brownells supply you with a tracking #), you will know if its been held,

you can email Dan (customs AO) in advance and let him know exactly what the part...

that and they don't give permits for A-cat parts, (unless its the action? and lower receiver?)

I Email Dan, tell him the trace# & what it is, its intended use (which is always A-cat)
because the arms office want a complete A-cat rifle before they will register it as a E-cat (Manukau)
and a...

a cat part... going into a cat AR

depends what your expecting, they will be different... but do you shoot well enough that it will make a difference?
I'd go the RRA, its actually $89.99usd (L6Q will give you 10$ off on a 99$...

got one of these ordered, AR-15 SABER DROP IN SINGLE STAGE TRIGGER | Brownells

$95usd - $10 discount as above, dunno if you get a shipping credit aswell atm with international shipping? will know...