The SAAMI 284 chamber in front of the case is just a shallow forcing cone (or leade, with less than half a degree taper per side) that starts at 0.2900" dia. In other words, it does not have a section of parallel freebore like most "match chambers" or the majority of more modern cartridge chambers. One of the defining traits of match chambers is a section of tight freebore with a thou or less clearance before the taper into the rifling. From what I have seen, having some snug freebore tends to make a rifle a little less picky when trying to find an accurate load. Although there is not just one "match chamber" spec, I would look into that option.
To provide a little background, Winchester was trying to get more powder volume by making the case as long as possible while still having a cartridge that could fit into a ~2.8" action/magazine originally designed for a 308-length cartridge.* This ended up reducing the amount of bullet protruding out of the case, so they did not add a section of regular freebore like the 308 has. Since you plan to load longer than the SAAMI-spec 2.800", you might want some freebore.
*Winchester later did a similar thing with the WSM series, but with considerably less slop at the beginning of the leade.
