Have you ever heard a rifle manufacturer say that their weapon has been “tuned” to run a certain ammunition while maintaining excellent recoil characteristics?
Do you believe that this is achieved by some sort of magic spell?
Well, if you do, I’m sorry to tell you that you’re wrong.
These manufacturers are simply paying close attention to important factors such as gas port diameter and location, action spring rate, buffer weight and construction, chamber dimensions, and so on. They thoroughly test their weapons to ensure function and allow the end user to put rounds on target in the most efficient manner possible.
Other manufacturers simply assemble an AR-15 out of parts, using components and methods selected to minimize production costs. Testing does not progress beyond exceptionally basic function and accuracy testing (if at all). If you asked such a manufacturer what the gas port diameter of a specific model was, and what testing led them to use that diameter, their answer would probably not be very impressive.
It’s difficult to describe why function isn’t enough. In my opinion, the AR-15 is at its best when it is a system that works in harmony with itself, not simply an amalgamation of parts constantly fighting one another.
To illustrate this point, I have high speed video (well, kinda high speed) of a 5.45x39mm AR-15 using three different buffers. Function with each was what some would call “perfect”. The weapon did not malfunction due to any of the buffer changes, and most folks would be content to use a carbine buffer, because it’s cheap, and “it works.”
What they don’t realize, though, is that the weight of the buffer is not as important when the action spring, extractor spring, magazine spring, etc are all in perfectly functional condition. The weight of the buffer becomes critical when said items begin to reach the end of their lifespan (or were never satisfactory to begin with), or when the weapon has been fired for thousands of rounds without any lubrication, or when various types of ammunition are used.
As you can see, the carbine buffer allowed the bolt carrier to bounce back after making contact with the receiver extension. Many people say that this isn’t a problem unless the weapon is firing full auto. While malfunctions are not as common on semi auto, is this really something you want your weapon doing? Even the heavier 9mm buffer allowed a similar amount of “bounce” – it doesn’t have the heavy internal weights of the carbine or H buffers. The BCM H buffer, though, with its heavier (and separate) internal weights, practically eliminated the issue.
The AR-15 platform is great due, in part, to its modularity. However, this modularity also allows inefficient combinations of parts to function with one another. By understanding how each component affects overall function, the last .01% of reliability can be achieved, and recoil characteristics can be improved.
I’d like to thank Mike Pannone for making me think hard about buffer weight and spring rate again, and especially the importance of the action spring.