DIY - Making Subsonic .223/5.56

I

IDT

New member
I've been tinkering around with making subsonic ammo for my suppressed 5.56. I threw together, today, a fairly terrible video giving a step-by-step instruction on how to make subsonic ammo for 5.56.

I'll create a better one later, but the info is in there:

Click here for the video
 
Okay video but I have one issue and one question.

First the issue, when you're talking about the powder moving around. In that portion you mention that if the powder isn't where it needs to be you won't get "full detonation" of your powder. Detonation is the last thing you want a smokeless powder to do, smokeless powder should only burn. Yes you can get detonation with smokeless powder, and when you do bad things can happen to the firearm and the shooter. That's why it isn't recommended to go lighter than the starting load with most smokeless powders.

Have you tested Trail Boss for position sensitivity? By all accounts I read on the Web this powder isn't sensitive at all to its position in the case. I'd like to know your chronograph results without using the cotton packing.
 
When discussing the detonation, I simply chose the wrong word. The word I should have used is Deflagrationwhich are thermal processes that proceed radially outward in all directions through the available fuel away from the ignition source. The description of what I was talking about is sound, I just used the wrong word.

In regards to the positional sensitivity:


Trail Boss powder was designed to fill the case and eliminate the issues of positional sensitivity. The IPDA (International Defense Pistol Association) is very acutely aware of positional sensitivity, which is why they have developed procedures for eliminating that issues with their 90 degree start. (not specifically for trail boss, but for powder in general.)

While Trail Boss is touted as being positional insensitive, there are differences in FP/S in regards to the position of the powder.

In previous Chrony testing I did about a year ago, I found that the differences in feet per second between having trail boss at the bullet end, the middle and the primer end were between 80 to 150 fp/s. That is slight enough for the manufacturer to declare the powder is not sensitive to position in the case. However for a subsonic round, especially ones that are close to the speed of sound, that could mean the difference between having a whisper quiet shot and having to deal with the crack of a sonic boom.

There is no downfall, other than time, to using the cotton as a filler and it can mean the difference between a 1050 fp/s shot and a 1200 fp/s shot - and depending on atmospheric conditions and barometric pressure, you may have just exceeded the speed of sound.

Personally, I'll keep my cotton filler and err on the side of caution.
 
The reason. I asked about positional sensitivity as guys have been using it in much larger cases without using filler material. If it gives you better accuracy and a lower SD then I see no reason for you to change your process.

the detonation slip is just a peeve of mine. It's kind of when people use caliber synonymous with what chamber the rifle is in. It isn't that big of a deal, you've obviously spent your time doing load development.
 
I wanted to look further into the differences between using and not using a cotton filler.

So, here is what I learned today.

I created two batches. Matched brass.
Batch 1 was using a 69gr Sierra Match King #1380 with 4.6 grains of Trail Boss and cotton filler
Batch 2 was using a 69gr Sierra Match King #1380 with 4.6 grains of Trail Boss and NO cotton filler

BATCH 1
Created: 12/10/14 01:02 PM
Description: 4.6gr Trailboss w/Cotton
Notes 1: Sierra 0.224 HPBT MatchK 1380 69 0
Distance to Chrono(FT): 5.00
Ballistic Coefficient: 0.296
Bullet Weight(gr): 69.00
Temp: 55 °F
BP: 30.15 inHg
Shots:
# FPS / FT-LBS
9 1005 / 155
8 1008 / 156
7 1032 / 163
6 994 / 151
5 1026 / 161
4 1032 / 163
3 1056 / 171
2 1028 / 162
1 1002 / 154
Average: 1020.3 FPS
SD: 19.5 FPS
Min: 994 FPS
Max: 1056 FPS
Spread: 62 FPS
Shot/sec: 0.2
True MV: 1022 FPS
Group Size (in): 0.00


BATCH 2
Created: 12/10/14 02:01 PM
Description: 4.6gr Trail Boss - no cotton
Notes 1: Sierra 0.224 HPBT MatchK 1380 69 0
Distance to Chrono(FT): 5.00
Ballistic Coefficient: 0.296
Bullet Weight(gr): 69.00
Temp: 55 °F
BP: 30.15 inHg
Shots:
# FPS / FT-LBS
11 1034 / 164
10 1092 / 183
9 1059 / 172
8 1083 / 180
7 1068 / 175
6 1292 / 256
5 1274 / 249
4 1115 / 191
3 1025 / 161
2 1124 / 194
1 1017 / 158
Average: 1107.5 FPS
SD: 93.4 FPS
Min: 1017 FPS
Max: 1292 FPS
Spread: 275 FPS
Shot/sec: 0.1
True MV: 1109 FPS
Group Size (in): 0.00


As you can see, the standard deviation on Batch 1 (with the cotton) was a fairly outstanding 19.5 with a spread of 62 while the standard deviation on Batch 2 was a fairly terrible 93.4 with a horrific spread of 275.

While I find it a bit odd, and worth more testing to confirm, that the absence of the cotton filler would cause higher velocities (due to slower burn and higher pressure possibly) I do think this is significant enough data at the moment to validate the use of a filler in the case and to counter any argument that says Trail Boss is a non-positional sensitive powder...it sure appears to be VERY sensitive at this point.

Note: I did have 2 rounds not read by the chrony in batch 1. However, if they were even remotely close the rest, the spread and SD wouldn't have changed much - and no guarantee it would have worsened.
 
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