Heavy Bolt lift on Tikka 6.5

[nephewjephew]

I have a tikka t3x (in a KRG bravo) 6.5cm shooting factory 147 eldm. I have 150-200 rounds down the gun and have not had one hiccup. Was shooting this weekend and the 3rd round in the mag (MDT 5rd poly mags) I had a really heavy bolt lift. I was shooting prone and had to break position and sit up to get the bolt to lift. And that continued for the next two rounds. Then switched mags and happened again the next two rounds. Switched to a new box and shot 3 or 4 no problem, then had a problem again. All but maybe 30 rounds has been in this stock, mags and ammo lot. I am no gun smith and don't reload, anyone got any ideas what may be happening here?

 

[General RE LEE]

Clean the chamber real good with a shotgun bronze brush and solvent. You may have gotten a carbon ring in the throat.

 

[General RE LEE]

Have you cleaned the rifle's bore at all?