- We acquired four identical Bushmaster AR-15 rifles. We chose the Bushmaster MOE Series AR-15 because it’s a widely available, affordable, and mass-market. We didn’t want something too cheap and of lower quality or something too expensive and of high quality since our goal is to help the most number of people.
- We acquired 10,000 rounds each of the following ammunition (new production):
- Federal 55gr – Brass-Cased – Copper Jacket
- Wolf 55gr FMJ – Steel-Cased with Polymer Coating – Bi-Metal Jacket (steel and copper)
- Tula 55gr FMJ – Steel-Cased with Polymer Coating – Bi-Metal Jacket (steel and copper)
- Brown Bear 55gr FMJ – Steel-Cased with Lacquer Coating – Bi-Metal Jacket (steel and copper)
- We paired each ammunition type with a specific Bushmaster AR-15 and then fired all 10,000 rounds of it through that particular carbine (except for Tula; more on that below)
- We systematically observed and tested various things, including (more details below):
- At the start: accuracy, velocity, chamber and gas port pressures, chamber cast
- After 2,000 rounds: accuracy, velocity
- After 4,000 rounds: accuracy, velocity
- After 5,000 rounds: throat erosion, chamber cast
- After 6,000 rounds: accuracy, velocity
- After 8,000 rounds: accuracy, velocity
- After 10,000 rounds: accuracy, velocity, chamber and gas port pressures, throat erosion, extractor wear, chamber cast, barrel wear
- We logged every malfunction of every rifle-ammo combination
- The rifles were cleaned according to a preset schedule and temperatures were monitored and kept within acceptable limits (more below)
- We sectioned the barrels and otherwise made unique observations after the test was complete
It’s a long detailed article, so budget some time for it. But you might want to bookmark it, because it’s full of interesting information, not least of which is the extent to which high-round-count guns, like military guns, get worn out.
My M&P-15T has never had more than a handful of steel-cased rounds through it. On the other hand, the Romanian AK has had almost nothing but lacquered steel-cased Golden Tiger through it.