Greg
The Ruger only holds 3 in the mag and one up the spout which was how I had them loaded for the shooting we were doing. On reflection it has always been the third or 4th shot to play up.
As they were factory loads I was assuming the crimp would have been done at the factory and should have been ok.This would mean an under crimped load at the factory which would be possible as I wouldnt think they would trim all the cases to the same length.

Because the boot from the factory ammo was more noticable when they popped and felt like the pressure was high I am tending to think it may have been a combination of
A) The lead being a little short
B) The dirty Barrel- definately my fault here.
C) The recoil causing the bullet to move into the case.

I have had no problem with handloads using 340 gr woodleighs and I have shot nearly 2 packets of woodleighs through the rifle. Havent had any more trouble with the factory 400grs either since cleaning the bore.

Would it be possible that the heat from firing a lot of loads- 40 odd rounds over maybe 45 minutes through the rifle would cause the cartridge to heat up and then create higher pressure?

In hindsight I doubt you would fire that many rounds during a normal hunt and maybe this also added to the problem.