The video examines how barrel length affects 5.56 muzzle velocity using PMC XTAC 55-grain ammunition. The host tests a range of AR-pattern firearms from a 7.5-inch Springfield Saint pistol up to a 20-inch Colt M16. Intermediate barrels include a Daniel Defense Mk18 with a 10.3-inch barrel, a PWS Mk11 with an 11.8-inch barrel, an IWI Zion with a 12.5-inch barrel, a Daniel Defense M4A1 with a 14.5-inch barrel, two 16-inch rifles (a SIG MCX short-stroke piston gun and an LWRCI direct-impingement gun), and a Daniel Defense Mk12 with an 18-inch barrel. The PMC XTAC box lists a muzzle velocity of about 3,120 feet per second, likely from a 24-inch test barrel. The goal is to record five shots per gun, average the velocities, and see how close each length comes to that figure.
The test begins with the 7.5-inch Springfield Saint pistol. Five shots produce velocities between roughly 2,149 and 2,229 feet per second, averaging 2,183 fps. Moving to the 10.3-inch Daniel Defense Mk18, velocities jump into the mid-2,400s to mid-2,500s, with an average of 2,513 fps, several hundred feet per second faster than the 7.5-inch barrel. The 11.8-inch PWS Mk11 shows another clear increase, with very consistent readings around the mid-2,600s and an average of 2,644 fps. The 12.5-inch IWI Zion pistol produces a more substantial jump, with shots in the mid-2,700s to mid-2,800s and an average of 2,789 fps. These results show that each few inches of added barrel length in this short range significantly boosts 5.56 velocity.
The host pauses to address common questions about optimal AR pistol barrel length. The 10.3, 11.8, and 12.5-inch barrels are highlighted as typical choices. Velocity differences of roughly 150 feet per second are observed between 10.3 and 11.8 inches and again between 11.8 and 12.5 inches. For maximizing 5.56 effectiveness, a longer barrel is recommended, unless compactness and maneuverability are the priority. The test then moves to a Daniel Defense M4A1 with a 14.5-inch barrel, classified as a rifle because the muzzle device is pinned and welded to meet the 16-inch legal length. Despite expectations, the 14.5-inch barrel averages about 2,763 fps, which is slightly lower than the 12.5-inch IWI Zion’s 2,789 fps in this session. The team repeats the 14.5-inch test and still finds only minimal difference from the 12.5-inch results, which they describe as surprising and somewhat confusing.
Next, the test compares two 16-inch rifles to see if operating system affects velocity. A 16-inch SIG MCX short-stroke piston rifle is fired first. Its five shots cluster tightly in the mid-2,800s, with an average of 2,865 fps. A 16-inch LWRCI direct-impingement rifle is then tested, equipped with an ACOG optic. Its velocities also fall in the high-2,800 fps range, averaging 2,872 fps. The difference between the MCX and the LWRCI is only a few feet per second, with the direct-impingement gun very slightly faster in this sample. The host notes that, in this test, the short-stroke piston system does not meaningfully change muzzle velocity compared to a similarly configured direct-impingement rifle when barrel length and ammunition are the same.
The Daniel Defense Mk12 with an 18-inch barrel is tested next, using a 20-round magazine. Velocities now approach and exceed 3,000 feet per second. Recorded shots include values around 2,962 fps and several readings at or just over 3,000 fps, with an average of 2,998 fps. This is the first configuration in the lineup to effectively reach the 3,000 fps region with the 55-grain 5.56 load. The host notes that, with this projectile weight, the jump into the 3,000 fps range can be significant for defeating hard targets and certain types of body armor, emphasizing that velocity is a key factor in terminal performance against harder materials. The 18-inch barrel clearly demonstrates a meaningful increase over the 16-inch rifles in this specific ammunition test.
The final rifle is a 20-inch Colt M16 with a 1:12 twist barrel, representing the configuration for which the original 55-grain 5.56 load was largely intended. Five shots produce velocities in the low-3,000 fps range, including readings such as 3,008 and 3,095 fps. The average comes out to 3,052 fps, making it the fastest of all tested barrel lengths. This still falls short of the 3,120 fps listed on the PMC XTAC box, which the host attributes to manufacturers typically using a 24-inch test barrel to establish published muzzle velocities. After reviewing the numbers, the video shows that velocity increases steadily from 7.5 to 16 inches, climbs further at 18 inches, and peaks with the 20-inch M16 in this lineup, while differences between certain intermediate lengths, such as 12.5 and 14.5 inches, can be smaller than expected in a single test session.
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