This article has been around the block a couple times... Secrets of the Houston Warehouse
In it, they make the statment that 21 3/4" is the magic barrel length but, they don't say where the measurment starts. I know for NFA stuff, you close the bolt, drop a cleaning rod down the barrel, mark & measure. After reading the article, I feel they are taking the measurment at the start of the lands because "Anyone who strictly observes the 21 3/4" doctrine will screw off a failing barrel of that length and run a new one under it. Rechambering and rethreading, in order to achieve more pristine lands just forward of the throat, shortens the barrel. Shorten the barrel, spoil the magic length.".
So, the question. Is barrel length measured from the bolt face or the start of the lands?
In it, they make the statment that 21 3/4" is the magic barrel length but, they don't say where the measurment starts. I know for NFA stuff, you close the bolt, drop a cleaning rod down the barrel, mark & measure. After reading the article, I feel they are taking the measurment at the start of the lands because "Anyone who strictly observes the 21 3/4" doctrine will screw off a failing barrel of that length and run a new one under it. Rechambering and rethreading, in order to achieve more pristine lands just forward of the throat, shortens the barrel. Shorten the barrel, spoil the magic length.".
So, the question. Is barrel length measured from the bolt face or the start of the lands?