Barrel speed up at 300 rounds?

[Troutslayer2]

I'm trying to figure out why now, at 300 rounds using the exact same process and materials my barrel is speeding up. Is this common? Proof barrel in 280AI went from a low ES around 2900 up to around 2930 FPS. I don't have a bore scope. This barrel has always seemed to prefer to be clean. I'm not sure what to expect from carbon ring and I don't know if that's my problem or if this barrel just took a while to break in. I do not anneal so could the hardness of the necks be holding my bullet tighter and causing the spike? Carbon ring? Just getting broken in? Magnetospeed not reliable?

 

[manitou]

My 280ai Bartlein barrel went 200 rounds before speeding up.