How long do they last/ hold their accuracy?

Depends.

Type of rifling.

How hot are your loads.

Cleaning regimen.

Etc., Etc.

forever

It sounds like from what users are posting, some pacnor polygonals have been shooting 2moa at 20K;
but from what I understand for some reason they are shooting well at 100 and that accuracy is not a normal ray measurement at other ranges- I would be interested in why, but I'm sure there aren't very many people with enough experience for the information to be readilly availible.

I can tell you M4 or A2 profiled Chome lined barrels will shoot like shit (3-5MOA at 100 meters at 5-10K rounds) Wether that is a ray measurement or not, I'm not sure, because the group is so big the rounds are randomly striking in a several foot radiused area at further than 250 meters.  At that point you select the point you want the shot to go and it decides where it wants to fly.



Another interesting point would be- If the A2/M4 is at 3-5MOA at 100 at 5-10K and the Pac Nor at 2MOA at 20k; are their corresponding groups going to be the same or different at 200+ meters.  [IE is their still a decided edge in a pacnor regardless of additional dispersion imparted with range?]

Another comparison would be both barrels at 10K the M4 at 5MOA and the Pac Nor at 1MOA [both at 100meters] comparing groups at 200+meters.