Testing the Effects of Suppressors on External Ballistics: .308 WIN & .300 Blackout

I wanted to test three threaded-muzzle bolt actions in a reference chambering well known to hunters and shooters, the .308 Winchester, along with a less-common bolt-action choice, the .300 AAC Blackout. The latter is more often chambered in AR-15 uppers because it has the same overall length, base diameter, and rim diameter as the 5.56 NATO round. It will feed from an unmodified magwell in an AR-15 lower. 

The .300 Blackout can be loaded with lighter bullets, where it compares favorably to the 7.62x39mm Soviet round or loaded with heavier bullets that travel below subsonic speeds for suppressor use. Subsonic ammo is easier to suppress at the muzzle, and it doesn’t create the downrange “crack” as the bullet breaks the sound barrier. At sea level, the speed of sound is roughly 1,125 fps, variance arising from air temperature and other conditions.

My first test rifle was a Savage 10PT-SR chambered in .308 Winchester. The bolt-action rifle featured a 5⁄8×24-threaded 18-inch barrel with a knurled-steel thread protector.

The first .300 Blackout rifle was a Remington Model 700 Special Purpose Synthetic SPS-T. The Model 700 SPS-Tactical has a heavy-contour 16.5-inch-long barrel and is muzzle cut with 5⁄8×24 threads. The SPS-T has a stubby 16.5-inch heavy-contour barrel 0.883-inch thick at the muzzle to have enough material to hold the threads and a can. The carbon-steel barrel has a twist rate of 1:7 inches. The 5-R rifling on the SPS-T is the same type as found on the company’s M24 SWS (Sniper Weapon System) rifle barrel.

There are five lands instead of six, as on a traditional barrel. Also, traditional lands are squared off at a 90-degree angle to the groove, while the lands on 5-R rifling are tapered at 110 degrees.

The third rifle was the Ruger American Rifle Ranch in .300 AAC. If you’re interested in the cartridge more than the rifle, Ruger also chambers an upper for the SR-556 Takedown in .300 BLK, as well as the Mini-14 Tactical Rifle. The Ranch Rifles come stocked with Flat Dark Earth synthetic units paired with a 16.12-inch alloy steel barrel, a muzzle diameter of 0.748 inch and a muzzle threading of 5⁄8×24. Like the Remington, the Ranch has a 1:7-inch right-hand twist.

To collect chronograph and accuracy data, I set up at American Shooting Centers in Houston (AMShootCenters.com). I recorded velocities using an Oehler Model 35 Proof Chronograph with the first screen set 10 feet from the muzzle. Velocities were recorded with an air temperature of 82 degrees and 90 percent humidity.

For bench-accuracy shooting at 100 yards, I fired the rifles off Caldwell DeadShot shooting bags. Accuracy is the average group size for 10 three-shot groups, measured center-to-center of the widest-apart bullet holes in each group, then rounded to the nearest tenth of an inch.

Suppressed data was collected with a Rugged Suppressors Surge 7.62.

The Surge 7.62 is a modular .30-caliber rifle silencer, which enables the shooter to change the size and configuration of the silencer. A removable tube section allows the shooter to go from a full-size 9-inch silencer to a shorter 7.5-inch unit. Also, by adding an interchangeable 5.56mm or 7.62mm endcap and respective muzzle devices for both calibers, the Surge 7.62 can be assembled as a 9- or 7.5-inch .30-caliber silencer rated up to .300 Remington Ultra Mag or as a 9- or 7.5-inch 5.56 silencer. Depending on the configuration, it weighs 17.5 to 21.5 ounces. It comes with a user manual and spanner tool to remove the endcap.

I shot the Surge in only the 9-inch model and was impressed with the .300 BLK suppression. According to Silencer Shop’s testing, the 9-inch configuration creates 122dB with subsonic .300 BLK, while the 7.5-inch format comes in at 128dB. When paired with 220-grain subsonic rounds, the report is barely noticeable.

My test ammunition included both supersonic and subsonic rounds. 

For the .308 Win. Savage, I chose Hornady Match 168-grain Boattail Hollowpoint, Monarch 145-grain Full Metal Jackets, and Winchester Super-X .308 Winchester 185-grain Power-Point JHP Subsonic. The .300 AAC Blackout rounds were Remington UMC .300 AAC 120-grain OTFB Supersonic, Remington UMC .300 AAC 220-grain Open-Tip Flat Base (OTFB) Subsonic, and Sellier & Bellot .300 AAC 147-grain Full Metal Jacket. The Savage .308 Win. shot consistently at 1 minute-of-angle (MOA) with the Hornady Match .308 Win. 168-grain boattail hollowpoints.

The average group sizes were 1.2 inches unsuppressed and 0.8 inch suppressed. The average velocity unsuppressed was 2,596 fps and 2,618 fps suppressed. The Monarch .308 Win. 145-grain FMJs shot 1.2-inch average groups both unsuppressed and suppressed and had respective average velocities of 2,685 fps and 2,668 fps unsuppressed and suppressed. The subsonic Winchester .308 Win. Super-X 185-grain hollowpoint shot slightly worse unsuppressed (1.4 inches) than it did suppressed (1.2 inches). 

The average velocity was 1,109 fps.

The .308 results slightly favored the suppressor’s use, with the Savage being noticeably more accurate with the Hornady rounds and close to a wash with the Monarch and Winchester loads.

The results for the .300 AAC in the Remington and Ruger rifles were substantially better with one round. Shooting the Remington 120-grain load, the SPS-T fired 1.4-inch unsuppressed average groups and 1.2-inch suppressed average groups, results mirrored by the Ruger with the same ammo. 

Average velocities were 2,222 fps unsuppressed, and 2,236 fps suppressed in the SPS-T and 2,210 fps unsuppressed, and 2,229 fps suppressed in the Ruger. Things improved markedly for both rifles shooting the Sellier & Bellot .300 AAC 147-grain FMJs. Both rifles shot this round into 1-inch groups unsuppressed and 0.8-inch average groups for the Ruger and a best-of-test 0.4-inch average group size in the Remington. Average velocities in the Remington were higher suppressed, 2,110 fps to 2,099 fps unsuppressed, and in the Ruger, 2,096 fps suppressed and 2,064 fps unsuppressed.

Shooting unsuppressed, neither rifle liked the 220-grain subsonic round from Remington, with the SPS-T shooting patterns, instead of groups, averaged 6 inches and the Ruger shooting 1.8-inch average groups. Suppressed was another matter altogether, with the Remington firing the namesake 220-grain round into 0.6-inch average groups and the Ruger also shooting well with 0.8-inch groups. 

The SPS-T shot 1,075 fps and 1,088 fps unsuppressed and suppressed, respectively, and the Ruger produced 1,073 fps and 1,089 fps unsuppressed and suppressed, respectively. Average velocities were all safely below supersonic.

Bottom line: Taken as a whole, the suppressed performance was uniformly better in both rifles and much better with the 147-grain S&B and 220-grain UMC rounds in the Remington and much better in the Ruger with the UMC rounds. 

This article is an excerpt from the Cartridges of the World, 17th Edition book!