Blair,

It sounds like you are on the right track.

When I have used felt wads I have seated the bullet to lightly compress the wads. Just lightly.

If your bullet wasn't seated to slight compression, then that could account for a difference in your load.

I'm now using backer rod, very lightly compressed.

If my rifle had regulated at 68 grains that's what I would shoot, so I certainly agree with you there.

Have you checked the cartridge in the left barrel after firing the right barrel to note any movement of the bullet? If everything is backing out the overall length will increase.

Ron,

The resident expert on the .577/650/75 loading is Marrakai. You probably have seen his posts on the subject. I'm not familiar enough with the ballistics of that round to voice an opinion. I would want to consult Wright's book, which isn't at hand right now. You have already done that.

As to the use of Varget, I had a hang-fire in my .577 with Varget. Marrakai and I discussed this in another thread. He was surprised to hear my reported hang-fire. We seemed to agree that my difference is the use of paper patched bullets as opposed to his use of jacketed bullets. Anyway, I'm not using Varget in my .577.

Curl