300BLK vs 7.62x39 | Subsonic & Supersonic Performance

Overview: 300 Blackout vs 7.62x39 Suppressed

The video is filmed at Take Aim Training Range in South Carolina and focuses on shooting suppressed with both subsonic and supersonic ammunition. The comparison centers on two popular calibers: 300 Blackout and 7.62x39. 300 Blackout is widely associated with suppressed and subsonic use, while subsonic 7.62x39 is less common in the United States, though more established in other regions. The goal is to compare sound, recoil characteristics, and velocity using a Garmin Xero chronograph. Both platforms are short-barreled rifles with similar barrel lengths and will share the same suppressor to keep the test as comparable as possible.

Galil 7.62x39 Setup and Adjustable Piston

The 7.62x39 test rifle is an IWI Galil equipped with an IWI IWS7 suppressor. In earlier use, the rifle ran reliably unsuppressed but showed cycling issues when suppressed due to increased back pressure. To address this, a KNS Precision adjustable long-stroke piston was installed. The piston features a dial that can be pushed and rotated to fine-tune the amount of gas vented, rather than relying on just one or two preset positions. This adjustability allows the shooter to tune the rifle for more comfortable and reliable operation with different loads, especially when switching between supersonic and subsonic 7.62x39 ammunition.

Ammo Choices and Test Plan

The 300 Blackout rifle is a SIG MCX Spear LT chambered in 300 Blackout, with a barrel length comparable to the Galil, in the 8–9 inch range. Previous testing on the channel suggested that 9 to 12 inches is a sweet spot for 300 Blackout performance. The IWS7 suppressor is moved between the Galil and the Spear LT to keep the comparison consistent. For 7.62x39, the subsonic load is a Hornady 255-grain round, which is significantly heavier than the 123-grain Bellum supersonic load. For 300 Blackout, the subsonic option is a Magtech 200-grain load, and the supersonic option is a Winchester 125-grain load. The plan is to shoot both supersonic and subsonic loads through each rifle, evaluate sound and recoil, and record velocities with the Garmin Xero.

Range Results with the Galil in 7.62x39

Testing begins with the Galil in 7.62x39 using the suppressor and the gas system initially set fully open. Supersonic Bellum 123-grain ammunition cycles, but when switching to Hornady 255-grain subsonic, the rifle struggles to cycle reliably. The KNS Precision adjustable piston is incrementally opened to increase gas, but even at the maximum setting the 255-grain load still fails to run consistently, though it is notably quiet. The test then moves to Brown Bear 196-grain subsonic 7.62x39. With this load, the Galil cycles properly and ejects cases with enough energy, showing that the adjustable piston can tune the rifle to run certain subsonic loads while very heavy 255-grain ammunition remains challenging in this short-barreled, suppressed configuration.

300 Blackout MCX Spear LT Gas Tuning

The suppressor is transferred to the SIG MCX Spear LT in 300 Blackout. The rifle is first fired with Winchester 125-grain supersonic ammunition, followed by Magtech 200-grain subsonic. The Spear LT features an adjustable gas block marked with plus and minus settings, indicating more or less gas. The rifle is fired with the gas set to a normal or higher setting, then adjusted toward less gas to see how it affects recoil. With reduced gas, recoil feels slightly softer while maintaining reliable cycling and bolt lock to the rear. The MCX gas system runs both supersonic and subsonic 300 Blackout loads smoothly with the same suppressor, demonstrating straightforward tuning compared to the more sensitive setup required for very heavy subsonic 7.62x39 in the Galil.

Shooter Impressions: Recoil and Sound

In terms of shooter feel, subsonic 7.62x39 is surprisingly close to subsonic 300 Blackout, though 300 Blackout feels somewhat softer. With the same suppressor and similar barrel lengths, subsonic 300 Blackout is perceived as quieter, while subsonic 7.62x39 is described as borderline hearing safe and slightly more bothersome to the ear. Supersonic 7.62x39 shows a stronger impulse compared with the tested 300 Blackout supersonic load, though the host rifles and ammunition choices influence this. Lighter 110-grain 300 Blackout loads, not used in this test, are noted from prior experience as having a sharper recoil than the 7.62x39 supersonic loads used here. Overall, for subsonic shooting from the shooter’s perspective, 300 Blackout is preferred for its softer feel and quieter report.

Chronograph Data for 7.62x39 Loads

Velocity testing begins with the Galil and Bellum 123-grain supersonic 7.62x39. Recorded speeds are around 2,000 feet per second, with readings such as 2000, 1894, 1934, and 1937 feet per second, showing consistent performance from the short barrel. Switching to subsonic 7.62x39, the chronograph is adjusted and records velocities around the mid-900 feet per second range, with one string averaging about 946 feet per second. The Hornady 255-grain subsonic load is then tested despite cycling issues. With the gas system at its most open setting, the rifle ejects but does not fully cycle. The chronograph shows velocities around 959 and 1007 feet per second. These readings indicate that the Hornady 255-grain load is very consistent in speed but requires more gas than the Galil’s configuration can provide for reliable operation.

Chronograph Data for 300 Blackout and Conclusions

The SIG MCX Spear LT in 300 Blackout is then chronographed with Winchester 125-grain supersonic ammunition. Velocities cluster tightly around 2,000 feet per second, with readings such as 2001, 1972, 1966, 1980, and 1992 feet per second. Magtech 200-grain subsonic 300 Blackout is tested next, producing velocities around 1,000 feet per second, including values like 1003 and 993 feet per second. Summarizing the results, subsonic 300 Blackout is clearly quieter than subsonic 7.62x39 through the same suppressor and similar barrel lengths, and it feels slightly softer in recoil. Subsonic 7.62x39 is usable but closer to the edge of comfortable sound levels. The MCX gas system handles both loads reliably with simple adjustment, while the Galil requires careful tuning and still struggles with very heavy 255-grain subsonic ammunition. From a shooter comfort standpoint, 300 Blackout is favored for subsonic suppressed use, while 7.62x39 remains widely used and effective with appropriate load selection.