Thread: Extraction problems

Hi guys I have been using a 7mm Mag for long range gong shots for the last year. Not using a super hot load Federal brass weight sorted 73gr 2225 under a Sierra 168 match doing about 2960fps with good accuracy hitting gongs out to 1600m. I have put about 700 rounds through it with no issues. During the last couple of shoots I have had about 30% of the brass with difficult extraction. The bolt is not stiff to lift but cannot draw the case out of the action. A sharp tap on the bolt handle with the ammo box or similar breaks it loose. The primers do not look overly flat and no other signs of over pressure. All case lengths checked no difference between the problem and no problem cases. At no time are the rounds chambered with any moisture on them as I know this can cause difficult extraction

During the last shoot in Culverden I segregated the cases that had the problem. On measuring them in front of the belt, problem cases .513 no problem cases.512 after sizing problem cases .512 no problem cases .511. So the die is not bringing all the cases back to the same size.

Before sizing if you re chamber a problem case it will chamber with non stiff bolt close but again will catch in the chamber again. If sized it will extract no problem.

As an aside I looked at the chamber and barrel with a mates bore scope to gauge throat erosion after 700 rounds to find no sign at all, I am using the David Tubb Boron Nitride bullet coating system. The one thing I did notice was the chamber how do I put this was not super smooth in that it looks like it needs a good polish and the brass always looks the same with very fine radial rings around them. I have tried to photograph but no easy.

My own thoughts are possible hotter batch of powder causing a lift is pressure. I need to rechrony loads to see if things have changed

Any semi sensible suggestions would be appreciated.