what is the standard barrel length for a ar?
Firearm Tutorials AR-15 barrel length. The AR-15 is perhaps the most popular carbine in America. It's commonly compared to the AK-47 despite the vast number of differences between the two weapons. While AR-15s are modular weapons meaning many of the parts can easily be replaced or upgraded, barrel length is often left unchanged at 16 inches. There are many reasons to deviate from the standard 16 barrel length. Many M16 rifles were built with a 20 barrel that gave it a little better accuracy. Some AR rifles are available with 20, 18, and 14.7 barrels are also become popular.