Love to have known this weeks ago, going to have to work backwards. Thanks for this.Ya, not the angle for bolt nose clearance. The radius around the rim of the chamber on the breech. If a person was to just run a reamer in, they'd have a sharp chamber edge. A Smith will radius that just slightly so a case or bullet isn't sliding over a sharp edge. The RimX requires a little more than normal based on the way the round enters the chamber and slides up the bolt face under the fixed extractor. The rear part of the bullet and case wall slides over the 6 o'clock chamber edge and forces the case head up the bolt face into a full horizontal attitude. Id recommend if someone is chambering a RimX for the first time they have an action present to test feeding. If you don't have enough chamfer it will feel like the round is binding as it enters the chamber. Because it is. Also, you have to be really diligent in setting your mag height correctly before you chamber a single round. Resist the urge to run a couple rounds right off the bat. Carefully watch the first couple rounds you chamber to ensure the rim is being captured under the extractor and not snapping over the rim. 3 out 4 guys I know locally and some of our shooting team guys have all buggered up their extractors and tensioners in the first 100rds. It doesn't take much to damage them. You tell them to ensure they have their mag height set properly and they're like, "...ya, ya,ya....right, right, right..." and then a week later they're asking you for a picture of your bolt face. It's a simple and easy fix to replace the extractor and tensioner and Zermatt is obviously easy to work with, but it's also completely avoidable.
Have fun with your new rifle! Show us some pics when you get it finished!