I think the posts above are accurate and they are consistent with the barrel expert Daniel Lilja. You might review his procedure outlined at Break-in Procedure
When an BR shooter and electron microscopist (PhD) pal of mine said skip barrel break in for these reasons .... I forwarded the email to Dan Lilja and Dan patiently explained the problems with his reasoning and why I should stick with his outlined break in procedures.
Note Dan specifically warns <font color="red"> AGAINST
</font> barrel break in with Moly.