A regular R700 action may struggle with 6BR and its variants. The plunger ejector isn’t ideal, and I had no end of problems. Approximately 1/2 of all shots ended up with the case still in the ejection port. No amount of fiddling with how hard I pulled the bolt back would fix it. I finally got fed up with it and had the barrel rechambered in 6 Competition Mach. Pretty similar to .243AI.
I did some research, and 6CM shooters are reporting barrel life of 4,000 + rounds when using Retumbo or H1000. I wouldn’t have believed it except a good friend has one with 4,500 rounds on the barrel and it’s still shooting into 3/4”. Not great, but good enough for the local long range matches around here.
It does require fire forming, so that may rule it out for you. I just finished mine recently, so I have no real results except to note that I could push Berger 109’s to 3100fps if I wanted. I selected a slower node to match my Dasher ballistics and hopefully get max barrel life.
Here’s a link to some more info.
https://www.longriflesinc.com/blogs/news/the-ins-outs-of-the-6mm-competition-match
