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New 6mm bbl.

21 Jan 2016
@ 12:33 am (GMT)

Paul Leverman

Hey all. First my apologies to all who responded to the bear story, I've been chaotically busy and haven't had a chance to be here lately. Now, it's all done and it's me time.

So, I've got my new barrel: 6mm c/w 1:8 twist, 5" of parallel, tapers from 1.250" to 0.845", will finish with 30" in front of the case.

Cleaned all the dust and crap out of it and had a look down the muzzle. Well, as far as you can see into a tiny hole like that. I was looking for the gun drill burrs as per Nathan's photos. What I found was not discussed anywhere in his books that I could find, but I'm older than dirt, and I probably missed it.

What I found were what looks like longitudinal marks. None that are horrible, in fact, you really have to hold it just right in the light to see them (with a 40X loupe). So the question is, do I pre-treat the barrel as per the regular break-in/lapping procedure? Or is it good to go?

Thanks for any help with this. I should mention that it isn't chambered yet, setting up a meet with the local 'smith, so this is kind of a pre-emptive question.

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21 Jan 2016
@ 01:14 am (GMT)

Nathan Foster

Re: New 6mm bbl.
Hi Paul, it may have already been lapped. Faint marks could reflect the difference between the finish on the shaped or cut stainless versus that of a lap- very hard to say.

If the barrel is a premium jobby, don't touch it. Get it chambered and break it in gently, see how it copper fouls and then decide on what steps to take as per the book instructions. The smith will mostly lap the chamber (even if just using JB's) to try and clean up reamer marks in the throat so it pays to back off doing anything until you have put shots through and can ascertain what is required.

If the barrel is a of a cheaper finish / brand then by all means, you may want to scotch lap it as per the book prior to chambering just to smooth it up a touch without making it too smooth or doing anything too drastic.

In either case, those first shots and the first three cleaning sessions are key factors.
21 Jan 2016
@ 04:28 am (GMT)

Paul Leverman

Re: New 6mm bbl.
Thanks, Nathan. Very helpful, as usual. It's supposed to be a premium barrel, so I thought I would check before proceeding.
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