16 vs 18 for 3gun

[cofi]

Not enough dwell time, so you need more gas and that defeats the benefits. 17" will work okay, but 18" is the sweet spot.

As Mark said, there isn't enough time after the bullet passes the gas port, but before it leaves the barrel to get enough gas into the system to work the action (dwell time).

Here is a link that does a pretty good job of explaining what happens, the good charts are at the bottom of the page: http://www.ar15barrels.com/prod/operation.shtml

The couple I have built have thousands of rounds of cheap Russian steel case through them I'd have to disagree....... softest shooting rifles I have ever shot like shooting a .22