Curious, what do your proof marks show and was the rifle marked as to intended load?

2 thoughts:
1) If your chosen 610grain does not regulate well you might look into the Woodleigh 650grain .577 BPE bullet, that was a typical Nitro for Black weight. Midway has them in stock.
http://www.midwayusa.com/product/129647/...=ProductFinding

2) as to chamber ringing; seems, from most reliable sources over the years, to be involved with reduced loads and shotgun/handgun powders such as Bullseye, Unique, 2400, etc.
Doubtful there is an issue with full power standard velocity loads using H4198 or similar and backer rod or Dacron.

I prefer backer rod in my .577, just less mess than the large wads of Dacron.
- Mike