I've been tinkering with handloading subsonic 5.56 for a while. I developed a nice subsonic 55 grain round a while back and just now getting around to working "down" a load for a 69 grain subsonic 5.56. Instead of creating a step-by-step post, I decided on making a video...unfortunately, it's fairly terrible. But the information is in there. One of these days, I'll get around to making a better quality video.

Click here for the video on subsonic 5.56 ammo

Work connection acting retarded, again. I will watch with enthusiasm when I get home.

Brilliant!

Presentation and exposition at the highest level.

Mechanics, care, attention to minute technical details, worthy of the best lab
procedures I have witnessed at any laboratory, Institute or Government.

Phenomenal results.

Kudos all around.

Many thanks for the inspirational and informative précis.

Best.

Historian wrote:Brilliant!

Presentation and exposition at the highest level.

Mechanics, care, attention to minute technical details, worthy of the best lab
procedures I have witnessed at any laboratory, Institute or Government.

Phenomenal results.

Kudos all around.

Many thanks for the inspirational and informative précis.

Best.

Wow. Thank you. Hopefully when I find the time I will be able to cobble together a much higher production value video on this for several different grain bullets. With more video of testing along with a db meter.

Well slap my bare ass and call me donkey! I really want to see it now...tick...tock...tick...tock...

Very interesting video, lots of details and information to absorb.
This winter I think I will work down a subsonic load of my own.

Thanks!

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.

great video sir

Will it cycle?

Nicely done but have you figured out what happens to the cotton?

double post....

saigatechusa wrote:Will it cycle?

It does not cycle. However, I"m both working on that AND debating why I should as the cycling action is MUCH louder than the actual shot.

este wrote:

este alludes to, without actually contributing to the benefit of this thread, that the 5.56 subsonic is nothing more than a .22 round. 55 seconds into the video I address that, so it's obvious he/she hasn't watched the video and is simply regurgitating a tired argument that has no basis in reality or physics.

Artful wrote:Nicely done but have you figured out what happens to the cotton?

As for the cotton - MOST burns up depending on how wispy you make it in the case. I've found a little (as in a very little) stuck to the edge of my first baffle of my suppressor. I can reach in with tweezers and grab it, or burn it out with a long match or just shoot a handfull of normal rounds where the hot gas gets rid of the cotton. I've got a 1 piece YHM suppressor and it's designed to not be cleaned - but those of you who have a take down kind of can, this won't ever be a problem as long as you clean your gear.

Really interesting, thanks for taking the time to make the video, I really enjoyed it. I need to start reloading, could you make a video on how to convince the wife

este isn't too far off at all, a 60gr Aguila SSS at 950 fps is hard to beat(no reloading needed). Not sure why you did your calculation at 700fps. They should yield about 120ft lbs at muzzle and cycle with a 22lr conversion.