Garand Thumb Tests Supersonic and Subsonic .300 Blackout in Ballistic Gel

Garand Thumb's channel revisited one of its most debated topics: how 300 Blackout actually performs when it hits gel. The crew brought back high-speed phantom camera footage, a chronograph, and a lineup of both supersonic and subsonic loads out of a 6.75-inch barrel, the length they say reflects what most militaries and agencies running the round actually field.

Key points

• Supersonic loads impressed across the board. The Sig 120-grain short-barrel copper round clocked 1,911 fps and produced what the host called an explosive compression with full penetration through the gel block.
• Even FMJ surprised the testers. Hornady Frontier's 125-grain FMJ showed more yaw at roughly seven inches of penetration than Sig's 125-grain OTM Marksman round, which the host said he did not expect from a basic FMJ.
• Subsonic rounds trade velocity for projectile design. The video explains that subs lack the speed to fragment or tumble like supersonics, so performance depends heavily on bullet construction rather than raw energy.
• The Sig 194-grain ME load stood out. Running at 867 fps, the solid-copper Lehigh-designed bullet petaled open dramatically in gel, which the host pointed to as a reason it sees use in certain units.
• 300 Blackout's versatility is the throughline. Garand Thumb notes the cartridge cycles both subsonic and supersonic ammo from the same gas setting, letting shooters stay quiet or switch to more power without changing hardware.

Quick take

For readers weighing 300 Blackout for a suppressed home-defense or truck gun setup, this video is a useful real-world look at how different loads actually behave, straight from the people putting them through gel on camera.

Watch the full video: Garand Thumb