Actually, some of the factory barrels were the same. It's widely known that 1920/26 barrels and M1899/99 barrels interchange and M20/26s show up with M1899/99 barrels. Several years back Numrich was selling M20 barrels and folks were buying them to install on M99s. All you have to do it examine the barrel markings.
It's all in the back posts.
