I started my long range addiction with a .22LR. A Savage MKll FV-SR. I use CCI Standard Velocity, and in the 16" barrel it remains subsonic. With a silencer it's quite enough to hear the bullet hit the dirt. I reverse engineered the military wind formula to come up with a formula to work with .22LR. I was quickly hitting metal plates at 300 yards and soon realized none of the birds were flying away. At 500 yards, it was very difficult to hit the targets I was shooting at with a 40 grain .22LR bullet going around 1070 fps at the muzzle. This lead me to ask the question, How would a subsonic 300 Blackout bullet work? A new journey began.
I started cutting down .223 LC brass to make 300 Blackout brass. I looked up factory ammo for the 300 Blackout and decided on Hornady 208 A-Max. I tested the 208 A-Max with H110 and IMR4198. Living at close to sea level, I knew I could push them a little faster knowing that the sound barrier was around 1137 fps. So, I was shooting for 1080 fps. However, I'll pick the most accurate recipe. I started a latter test with H110 8.2 - 9.6 grains each in .2 grain increments. With IMR4198 I went with 10.5 grains and settled on 9.1 grains of H110, giving me a velocity between 1070 and 1100 fps. I was using an F-1 chronograph. At this time I was still new to long range shooting, but I thought I knew enough. At 100 yards I was shooting 1 inch groups. I tested different neck tension and nothing seemed to produce smaller groups. So on to 200 yards I went.
At 200 yards, I quickly noticed larger groups but it was still reasonable. Wind deflection was not horrible, but it was not great either. Over all, at two hundred yards, it’s fun to shoot steel with subsonic ammunition. It’s amazingly quiet and extremely satisfying to hear the hit on a steel plate. At 300 yards or more everything just drops off a cliff. I wasn’t able to make hits with any reasonable consistency or accuracy. I can tell you this, I wasted a lot of bullets, primers and powder to find this out. I don’t give up easily and this was no exception. But, I did exhaust every idea that I could think of to get these bullets to work. I came up with two ideas of why the failure. One was the extreme spread and standard deviation, and the second was the powder charge relative to the case capacity. Specifically, that there is such little powder and such a heavy bullet, that I couldn’t get consistent velocity. This leaves me to believe that there is more that can be done to get 300 Blackout to shoot successfully at longer ranges. Now, I just need to come up with a plan to carry out more testing with out unnecessarily waisting more ammunition. What I am going to test is if turning the case neck will affect accuracy versus non turned necks. I will also test lighter bullets with different powders to see if it will make any improvements and combining lighter bullets with neck turning. While a lighter bullet will not have as high a BC, if it’s more consistent then the trade off should be worth it.
Standard Deviation
From my testing I believe the biggest negative effect for accuracy when shooting subsonic ammunition is the standard deviation. Standard deviation is the difference in velocity between rounds that are faster or slower than your groups average. There are a few inconsistencies that can cause this like, powder charge, ignition, neck tension and even inconsistencies in the brass itself. I am currently working on minimizing the inconsistencies and live fire testing to see if it is possible to hold 1 MOA group at short and medium ranges. Let’s look at the data of standard deviation and the affects is has on subsonic 300 Blackout.
I’m gathering this data by using a ballistic app and using the drop data for 1,058 FPS and subtracting the drop data from 1,080 FPS. It should be understood that this is not a true representation of a gropes size, but a representation of the groups size based on the fastest and slowest bullet from the groups average. This does not include extreme spread.
With the velocity of 1080 FPS and a standard deviation of 22 FPS, the spread changes dramatically.
200 yards - 1.1 inches
300 yards - 3.2 inches
400 yards - 6.4 inches
500 yards - 10.6 inches
600 yards - 15.8 inches
Now, if I add in the 1 MOA for every 100 yards you can quickly see why it’s difficult to shoot subsonic loads accurately at further distances.
200 yards - 3.1 inches
300 yards - 6.2 inches
400 yards - 10.4 inches
500 yards - 15.6 inches
600 yards - 21.8 inches
Let’s compare this to .308 Winchester using the same parameters.
200 yards - .1 inches
300 yards - .35 inches
400 yards - .7 inches
500 yards - 1.3 inches
600 yards - 2.0 inches
With 1 MOA per 100 yards.
200 yards - 2.1 inches
300 yards - 3.35 inches
400 yards - 4.7 inches
500 yards - 6.3 inches
600 yards - 8.0 inches
As you can see from the data above, when we compare supersonic data to subsonic data with a 22 FPS difference, the characteristics differ dramatically. But, this is only taking into account the standard deviation. If we add in the extreme spread, it get worse. Not to mention, that a subsonic bullet is moving much slower than a supersonic bullet, so all the environmental effects will have more time to change its trajectory.
Extreme Spread
Extreme spread is the difference between the fastest and slowest bullet within a group. While standard deviation is directly related to the groups average, it’s also important to see how the extreme spread can affect a gropes total size. Using the same formula above to collect this data we will only be looking at the fastest and slowest bullet within a given group.
200 yards - 2.5 inches or 1.19 MOA
300 yards - 7.5 inches or 2.38 MOA
400 yards - 14.8 inches or 3.53 MOA
500 yards - 24.6 inches or 4.69 MOA
600 yards - 36.8 inches or 5.85 MOA
Based on this data, if I define the maximum effective range for a subsonic 300 Blackout round as being able to hit a 10 inch target with 100% accuracy, then the maximum effective range is just under 300 yards. For just shooting at the range that’s not bad at all. I have seen people miss bigger targets at closer ranges. However, I wouldn’t call that very accurate or precise. I would call it a fun and quiet day at the range.
Looking at this data it is going to be very difficult to get a 300 Blackout shooting subsonic ammunition to shoot accurately. But, there are things that can be done to minimize the standard deviation. I have three loads worked up to test using different primers. As of now I’m using CCI small rifle primers but i’ll test out small rifle magnum primers to see if I get better powder ignition. I will also be testing out if case neck thickness will have any change by turning case necks. This should help minimize case neck runout. If both of these ideas work, I should be able to increase the maximum effective range of this round when it comes to accuracy. I’ll also be testing lighter bullets in the 110 and 125 grain range to see if there is any difference their as well. Right now, all of my testing has been done using 208 grain Hornady ELD-M bullets. I did a 5 round group test with 110 grain Barnes black tip subsonic with extremely surprising results. So, there is a light at the end of this tunnel.
To follow along on this 300 Blackout journey, please Subscribe to my Youtube channel where all the video data will be added.
The Overwatch
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