Hiya Ned
Mate, have you ever seen how they run in a race engine?, I think its fair to say a race engine can be compared to a top performing rifle yes?
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Finish building it and then rev the living shit out of it, basically that's how I run all my cars in, and yes, I buy them new, and also that's how I run my rifles in.
I have yet to blow an engine up, and if you ask anyone that's ever been in a car with me, I don't drive softly. I have also never burnt a barrel out of any rifle I have ever owned. Granted I do not shoot bench rest comps, but I will head shoot roo's 19 times out or 20.
For a hunting rifle, I reckon you are pulling ya pud running it in, on a comp rifle, if it makes you feel better, go for it, but I'll bet my left one it doesn't make a zac of difference