Sub Sonic .308 win

[Yeti]

.308 GOING SUB-SONIC

Here is how I went Sub-Sonic.
What follows worked for me, and if done correctly is very safe in my rifle. Savage , 26 inch barrel with a 1/10 Twist
This is not to say your results will be the same as there are just too many variables.
But this may act as a guideline, for someone wanting to try the same.
In layman’s terms the speed of sound is around 1116 Feet per second.
So I strived for a constant, reliable speed that will reliably go sub sonic, as just one round that goes supersonic, will defeat the entire exercise.

INGREDIENTS:

1. Full length sized PMP .308 Win Brass (Spare PMP Brass is what I had)(Neck sizing will work just fine too)
2. Winchester Large Rifle Primers (I do not use Magnum Primers)
3. 3.0 mm Drill Bit
4. Somchem MP200 (Handgun powder)
5. Hornady .30 cal 170 grain Flat Nose, Flat base bullet (As used in Tube fed, Lever actions) I tried some Sierra pro Hunter 180 gr (Flat Base) and some Gamekings (boat tail) Bullets, but accuracy was awful out of my rifle.
6. Dacron, no one seems to know what this is, so go to your local pet store and ask for the “fluffy white stuff” to use in your fish tank filter. It comes in a small plastic bag and is inexpensive. Do not be tempted to get more than one bag, as one is plenty.
When selecting a bullet, bear in mind that your velocity is a fixed entity, so you may as well go for a bullet on the heavier side, as this will ensure more energy than a lighter bullet and will in most cases stabilise better at these low velocities.

METHOD:

1. Select the no of cases you intend using for your sub sonic loads. Please note that you will not be able to use these cases for “normal rounds again” Mark them as to not confuse them with Normal brass. I used a permanent Black Marker on the bases of all the selected cases and I made a point of putting them in their own, well-Marked Ammo holder (See Photo). I also filled the ammo box, so that at a glance I can see if one is missing etc.
2. Drill and enlarge all the Primer Flash holes to a 3.00 mm
3. Prime all the cases
4. Use 8.00 grains, that’s EIGHT grains MP200 powder.
5. Pull out a tuft of Dacron and compress and roll it between your dry fingers. How much Dacron to use is hard to answer, but when you think you have too little, half it ! I found that if I can get it in the mouth of the case with my fingers, it’s probably too little. When I need the assistance of the sharpened end of a pencil to effortlessly guide and press it in, then the amount is about right. Once the Dacron is in the case neck, insert the blunt end of the pencil (typical HB school type) into the case neck and “stomp,” Compress the Dacron on top of the powder charge. The springy, spongy properties of the Dacron will keep the powder charge compressed against the Primer flash hole.
6. Insert the bullet and seat as per normal to a COL that suites you. In my case this was a COL of 66.00 mm
7. I place all my loaded Sub sonics Bullet up, in their cartridge box, thus ensuring the charge cannot slip forward away from the primer if the case is shaken and rattled, as would be the case on a rough gravel road etc.

OBSERVATIONS:

Loaded accurately, 7.50 Grains MP200 gave me an average of 974 Fps, too slow. With a large Extreme spread.
8.50 grains MP200 was too fast at 1126 Fps.
8.00 grains MP200 gave very consistent speeds, never went supersonic (Highveld altitude) 1050 Fps Average velocity.
As there is so little powder in the case, it’s easy to load a double or even triple charge! Don’t do that! Be conscientious and systematic with your charging and loading procedure.
Same can be said of seating a bullet, without a charge at all, don’t do that either!
Doing the whole Dacron thing is painful, don’t be tempted to exclude this important component. Loading subsonic ammo is not for the impatient.
I shot this load out to 100 meters and the trajectory is simply put, appalling! More akin to the shape of a rainbow.
10 shot, at 100 m group shown in pic. Not too bad for my first try at that distance.
Energy at the muzzle is very low, in my case 416 Fpe and gets less by the foot.
Please ensure that every bullet leaves the barrel, before firing another. At these energy levels, I doubt a bullet will get stuck, but better safe than sorry.
Recoil is non-existent.
It’s fun, but I cannot for the life of me imagine a practical application for these subsonic rounds?
I personally wouldn’t use them for hunting
Maybe for training the younger members of the family? An air rifle would be a better and far more cost effective choice.