AMAZING 308 Subsonic Loads (and fun too)

Hornady produces a bullet specifically for subsonic use, the Sub-X. We’re trying it in the short barreled 308 Winchester, “Shorty.” Berry’s offers a fine inexpensive bullet as well.

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308 “Shorty” Recap

Our 308 “Shorty” build seemed ideal for use with heavy bullet subsonic ammunition. It’s also become one of my favorite rifles.

The Benchmark barrel has a tight 1:8.5 twist, much faster than a typical 308 Winchester barrel, set in a BAT Igniter action and Foundation Dominion stock. The Trigger Tech Remington 700 Special Trigger is of course a delight to use.

This was my first time using the Leupold Mark 5 HD 2-10 x 30 scope. It seems well suited for a variety of uses, including hunting. The optic was clear and bright, the adjustments crisp. 2x is perfect for short range use as the wide field of view helps the shooter get on target quickly. 10x is plenty of magnification for most hunting and many “tactical” situations. When I had a USMC STA platoon, our snipers used fixed 10x Unertl scopes and shot well with them.

The BANISH 30 suppressor mounted easily to the ⅝ x 24 threads Gavin had cut into the Benchmark barrel and stayed firmly in place after hand-tightening. With the subsonic loads, the rifle was incredibly quiet. The sound of the bullet striking the target was louder than the rifle firing and of course there was no supersonic crack either. This made for a very pleasant shooting experience.

About the Loads

Hodgdon has published an extensive amount of subsonic load data, including for the 308 Winchester.

We had a useful quantity of two of the powders listed, H4895 and Trail Boss.

About Hornady’s 30 Caliber 190 Grain Sub-X

From Hornady:

Sub-X® (Subsonic — expanding) bullets deliver big results without a big bang! Designed to provide deep penetration below the speed of sound, Sub-X® features a lead core. Long grooves in its gilding metal jacket combine with its flat profile and the patented Flex Tip® insert within the bullet’s hollowpoint cavity to help it expand reliably at low velocities. Cannelures provide positive case crimp, making Sub-X® ideal for semiautomatic weapons.

This bullet is recommended for medium game up to 300 pounds.

About Berry’s .30 Caliber 220 Grain Plated Bullet

This 220 grain is one of Berry’s plated bullets. Note that the copper plating is NOT the same as a conventional jacketed bullet!

This bullet is rated for a maximum muzzle velocity of 1300 fps with a recommended 1:7 barrel twist rate to stabilize it. This bullet was specifically developed for the 300 Blackout cartridge and we have used it in that cartridge before.

From Berry’s:

If you like reloading your own ammunition, we have the finest bonded copper-jacketed bullets available. Our bullets start with a swaged lead core and are then electroplated with copper to their final weight, leaving no lead exposure. Finally, they are re-stuck to precise specifications to ensure a solid bond and consistency across every round. Our 300 AAC BLK bullets are indoor range safe and unbelievably accurate. Find out today why shooters around the world love Berry’s Superior Plated Bullets®.

Load data for our Superior Plated Bullets® can be found in any manual or on any powder manufacturer’s website.
Cast or jacketed data with the same grain weight and profile will work with our bullets.
You can use a taper or a roll crimp.
Don’t over crimp the brass after seating. This causes bullet core separation, leading to increased copper fouling and accuracy issues.
Don’t exceed the recommended maximum velocities listed. This creates bullet core separation and accuracy issues.

Loading

The ammunition was assembled at my home on the Lyman Brass Smith All American 8 turret press using Redding National Match dies.

I primed the once-fired R-P 308 cases using the Frankford Arsenal hand priming tool and CCI 200 Large Rifle primers.

Caution! While loading the tiny amount of 13.3 grains of H4895, there is plenty of room in the 308 case for a double charge. Use caution while loading and check your cases for the proper powder charge before seating a bullet. Trail Boss is a uniquely shaped, particularly bulky powder and fills the case enough to prevent double charging. It should not be compressed.

Trail Boss Powder in the Lyman Gen 6 Powder Measure

Chronograph & Accuracy Results

The H4895 ammo was a bit of a disappointment, achieving only 802 fps with a fairly wide variation in velocity. Accuracy was mediocre and the cases were sooty after firing, an indication that the pressure was quite low and that the case wasn’t expanding enough to seal the chamber.

I suspect that increasing the powder charge would have improved things considerably as H4895 does have a reputation for producing excellent accuracy and is often used for reduced charges. It has certainly been a fine powder when I’ve used it for normal velocity rifle loads.

Berry’s 220 grain plated bullets with Trail Boss

Trail Boss worked wonderfully in these subsonic loads! First developed for low velocity lead bullet revolver loads, it’s also useful in some rifle applications, such as this one. I’ve used Trail Boss in other low velocity rifle loads, but never before in the 308 Winchester. Hodgdon and IMR have provided some guidance for how to safely use Trail Boss for low velocity loads from rifle cartridges.

From IMR & Hodgdon:

IMR® TRAIL BOSS® REDUCED LOADS FOR RIFLE AND PISTOL As noted in the powder description section, Trail Boss was designed primarily for reduced loads using lead bullets in pistol cartridges. However, Trail Boss offers superb versatility in rifle cartridges producing reduced loads using lead or jacketed bullets. These reduced loads make firing such cartridges as the 300 Winchester Magnum or even the 458 Winchester Magnum pure fun! Where data is already shown for specific cartridges, never exceed listed maximums. Many original black powder pistol cartridges have capacities where a full case to the base of the intended bullet, creates charges that exceed maximum pressures allowed by SAAMI. In all these cartridges, we show data that stays within the SAAMI maximum pressure guidelines. Listed below we show a few examples of rifle loads throughout the Reloading Data Center, but the fun doesn’t stop there. If you don’t see Trail Boss data for your favorite cartridge we have a formula for developing loads for all cartridges and it’s simple to follow. This formula may be used in both rifle and pistol applications:

1) Find where the base of the bullet to be loaded is located in the case and make a mark on the outside of the case at this location. Then fill the case to that mark with Trail Boss, pour into the scale pan and weigh. This is your maximum load. Pressures will be below the maximum allowed for this cartridge and perfectly safe to use!

2) Take 70% of this powder charge weight (multiply the maximum load from step 1 by .7), and that is your starting load.

3) Start with this beginning load and work up to your maximum charge, all the while searching for the most accurate reduced load. Once found, the fun begins!

One target in particular caught my attention. I was adjusting the point of impact at 50 yards and the bullets clustered into a tiny group. I wasn’t able to shoot quite as well at 100 yards, but the groups at 50 showed that there is good accuracy potential here. I’m sure a little load tuning and/or more time with this rifle would produce better results.

50 yard target, 220 gr Berry’s Bullets. Four in the cluster and I pulled the high shot.

Ballistics Gel Results

I also thought it would be interesting to look at some 300 Blackout ballistics gel results with roughly the same velocity as our subsonic 308 Winchester load (190 grain Hornady Sub-X with muzzle velocity of 1088 fps).

Penetration in the Clear Ballistics gel blocks was 17” while the recovered bullet weighed 187.94 grains and expanded to .463” diameter.

Conclusion

The 16” 1:8.5 twist Benchmark barrel seems ideal for stabilizing heavy bullets, even at low velocity. I can see a couple of potential uses for the subsonic ammo.

Loaded Berry’s 220 grain bullet (left) and Hornady 190 grain Sub-X (right)

With Hornady’s 190 grain Sub-X it could serve well as a modest range hunting bullet for game up to 300 pounds or so. This includes most deer, bear and wild hogs taken in North America annually. With the 220 grain Berry’s full plated bullet, it would be an excellent training tool! That bullet showed excellent accuracy potential and is priced well. I can’t help but think that with low velocity plated ammunition, barrel life should be excellent. Kyle and I noted that the barrel on the “Shorty” rifle barely warmed up while shooting dozens of rounds of subsonic 308 ammunition.

We observed greater accuracy and consistency with Trail Boss over H4895 in all of our tests.

I did note a huge difference in the point of impact when using the subsonic ammunition after the rifle had been zeroed with conventional ammunition. At 50 yards my first shots were off the 8.5×11 paper! At 100 yards it wasn’t even close and required a lot of elevation to be dialed as a correction.