Hi All, While doing some research, I noticed some differences between a factory chamber and a reamed from Win Mag chamber. This would impact developed hand loads and is something for hand loaders to be aware of and take extra care when using other peoples loads. If you look at the SAAMI picture of a Win Mag chamber, you will see it has a long 'weatherby ' throat as the chamber goes from cartridge diameter into the barrel/rifling diameter. This design helps the win mag get as much velocity as it can before the bullet is forced into the barrel/lands in a similar way to weatherby rifles. It also means that Win Mag handloads can have the bullet set out of the brass by a long way before it gets close to the rifling. The win mag throat would allow approx. 28 mm (1 1/10 in) of freebore before the rifling. You can pretty much match the length of the Lott cartridge with the right bullet (banded monolithics with lots of crimping grooves). Essentially the freebore extends to approx. 92 mm. The Lott chamber is longer but has a more conventional throat. You can see below that the chamber to rifling distance is about 8 mm (1/3 in). The freebore only extends to a total distance of 79.5 mm. That means if you ream out a Win Mag chamber to Lott, you will be left with almost 10 mm of the long Win Mag throat beyond a factory Lott chamber. This extra 10 mm of free bore is quite significant. I would expect higher velocities from a reamed chamber vs factory and also lower pressures. After all, that is why Weatherby allows so much freebore.Handloaders can also stretch the Lott OAL, seating bullets out for more powder capacity if your mag length allows in a reamed chamber.