At this point I'd go back to basics as US869 should NOT be worse than Retumbo. 50-60 extreme spread could be other things, like diffrence in brass thickness from case to case. If all case prep has been done precisely and you have sorted brass to form a control group and still having 50-60 extreme spread, you are closer.
I would also look at copper fouling, (Is this a factory gun???). High velocity 7mms are very prone to copper fouling. And Factory barrels are certainly not the smoothest. Are there imperfections, like tooling marks or burs?? One would think that It's not a big deal, but it really can be.
I actually had a 7mm Rem Mag in a Sendero that had a tight barrel. It was accurate enough, but ran 200fps slower than 3 other 7mm Rem Mags that I Chronyed on the same day with the same load. It ended up having a tight barrel by a few Thousandths.
You have mentioned Extreme spreads, but how is the accuracy?? ES aren't a big deal unless the accuracy isn't there..and if shooting at reasonable ranges. Are you trying to make this a target rifle or just hunting? I'm not trying to tell you to settle, but you need to realize the limits of a factory rifle.
You can lap the barrel to smooth it out, either by fire lapping (last resort) or hand lapping with a tight jag and lots of elbow grease. (I did this for the Sendero and it helped with the ES for that rifle by dropping it from 70-80 to 40-50FPS, It was a marked improvement.) Copper fouling was also reduced.
I hope I'm being helpful, Just trying to think of diffrent ideas.
Dan
