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My first attempt at loading .300BO subsonic (Velo results - ongoing)

Bushwhacker

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So like most people, I love shooting my suppressed .300BO subsonic. After years of accumulating components and putting it off I finally started load development for subsonic 300BO loads. This is an ongoing process as they always are. I wanted to share my findings thus far and will update the thread as I continue development. This may be WAY to much info for a lot of people to read thru, but know this kind of info would have saved me time and money. As usual these results are my own for my specific setup/situation. Consult published load data from reputable manufactures. My loads may produce different results than others and my not be safe for your gun. With that out of the way, here's where I'm at thus far. * Note moa wasn't measured, because I want consistent velocities first, So I'd say all loads produced 2"-4" MOA at 50 yards on bags (not good but didn't care about that during these test)

Firearm: I built an SBR a few years ago
Recievers: Aero Precision
Barrel: 10.3" Daniel Defense (results will definitely vary based on barrel length)
BCG : Gemtech
Handguard : Seekins Precision
Trigger : Giesele
Buffer : Spikes H2
Gas block/tube : Odin Works
Stock: MFT minimalist

For this load: (5 shot groups)
Projectile - 200gr Berry's plated SP. (I'm also working on a 220gr Berry's load development)
Primer - S&B Small Rifle Primer
Brass - (Mixed factory 300BO)
Powder - CFE BLK (will be working a couple others in the near future)
COAL - 2.260"
Temperature: Between 55 -70 degrees f
I worked in reverse of normal load development since I'm trying to achieve a safe, accurate, consistent subsonic speed with as much KE as possible.
** It's worth noting, every load ejected and achieved last round bolt hold open. The lowest charge weight produced one fail to load. I also only had 1 load go supersonic**

Load #1 -14.0gr CFE BLK
Avg Velo = 1095fps
max - 1164fps (Supersonic)
min - 1057fps
Extreme Spread = 107fps
Standard Deviation = 41fps

Load #2 - 13.6gr CFE BLK
Avg Velo = 1004ps
max - 1072fps
min - 964fps
E/S = 108fps
SD = 43fps

Load #3 - 13.2gr CFE BLK
Avg Velo = 983fps
max - 1063fps
min - 926fps
E/S = 137fps
SD = 45fps

Load #4 - 12.8 gr CFE BLK
Avg Velo = 949
max - 1087fps
min - 895fps
E/S - 192fps
SD - 72fps

Load #5 - 12.2gr CFE BLK
Avg velo= 889fps
E/S = 124fps
SD = 42fps

Load #6 - 11.8gr CFE BLK
Avg velo = 781fps
E/S = 237fps
SD = 77fps

Load #7 - 11.3gr CFE BLK
Avg Velo = 726fps
E/S = 110fps
SD = 42fps

Load #8 - 11.0gr CFE BLK (Entirely too slow velo, but did produce the best E/S and SD numbers. Also had one fail to load, it picked up a round but didn't fully return to battery)
Avg Velo = 721fps
E/S = 61fps
SD = 25fps


Anything below Load #4 is a waste of time/money in my setup.

So I've already loaded the next 3 loads (13.7gr, 13.8gr and 13.9gr), which is between Load #1 and Load #2, just waiting for a day with somewhat similar temps to previous loads. Based on the results so far, one of those should give me an average around 1050fps, hopefully with E/S in the double digits at least and an SD in the teen's to low 20's but that's being wishful.
 
Solid work! It’s neat to see load development progress, isn’t it? Are you sorting and loading your brass by headstamp? If not, limiting the variance in case volume between different brass headstamps may help achieve the lower E/S and consistent velocities you’re after. Keep us updated!
 
I gave up on cfe black for subs, never could get the velocity spread to not be all over the board. May have just been me though. I did find that the Vihtavuori powders didn’t have that issue plus they burn alot cleaner. N120 seemed to be the best for function suppressed or unsuppressed. However N105 is the quietest but it will not cycle the action reliably unsuppressed. H2 buffer?
 
May want to try some other powders. Of course CFE Black was designed specifically for Black Out I believe. Give Lil'gun a try, it has been stellar in 125 grain super loads. IMR4227 may also be a good powder to try.

Rosewood
 
H110 for 110gr and 120Gr supers, 1680 for subs 180 - 220gr, running in my build with a DD10.3" barrel with a suppressor. Have tried CFE Black on subs, but in my pistol 1680 works better and is cleaner (relatively, but suppressor = carbon)
 
Those SDs are way too high. It'll be hard to get any consistency on subs with those numbers.

W296/H110 may work, but I didnt have as much luck with a 10.5 barrel as I did with a 7.5"

1680 is a really good one for subs because it has so much gas. It'll cycle at lower charges.
 
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