Well... if pulling a soft nylon string from chamber to mouth a few times after shooting 20 to 40 rounds is going to "wear a bell shape" in a hardened steel barrel crown, I do not want to even think about what hard mono-metal bullets or steel jacketed "solids" or gilding zinc alloy jacketed "softs" passing at 3,000 + fps, under 60,000 + psi of pressure, and pushed by cutting torch-hot 3,300 + F combustion gases jetting between the crown and the bullet base as it exits the crown, will do to it
If Bore Snakes "will destroy accuracy" I guess that my Steyr SSG 69; Mk 11; Mk 12; and Mk 13 did not get the memo, because they continue to shoot 1/4 to 1/2 MOA groups out to 600, 800 and 1,200 yd (depending on caliber) day in, day out, despite years to decades (depending on how old the rifle is) of having a bell shape worn out of their crown every few weeks...
Note: I only attach pictures to document that I actually own the rifles and I am not making it up
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As to the "soft string will contain abrasive material after a few uses" my experience is that the embedded bronze brush pushes everything out of the barrel (you can actually see the bristles project forward a small cloud of powder residue when the brush section pops out of the crown). Beside, should the bore snake become really dirty, you can wash it...
Totally +1 on that too. The voice of actual experience
Been there too 20 years ago
Yep, to each his own...