Slowing down Blackout Subs

[Roadhawg]

I just got back from testing some subsonic rounds.
I have a 16" barrel with a pistol gas system.
The following are 10 rounds averages, all cycled the gun and had bolt hold open. Overall the 220gr Gorilla was the best performing of all. I am a little concerned with case fill if I drop my the weight of 1680 lower.

208gr Amax 2.220" 10.8gr 1680 1171fps
208gr Amax 2.220" 10.6gr 1680 1155fps
208gr Amax 2.220" 10.4gr 1680 1124fps

Factory rounds
208gr Hornady Amax 1138fps
220gr Gorilla 1044fps

 

[Rockn93yj]

I'm using 16" YHM barrel carbine with the 300 blackout buffer spring and suppressor. I use 10.2gr of 1680 with 208 gr A-max resulting in a 1.3" shot group. My average was 920 fps, still cycled and bolt hold back on last round and gave me the most accurate round. I started wtih 10.0 and worked by way up to 11.0. 11.0 was amount that sent it super. The higher the charge went the larger the shot group went.

 

[Speed3]

Good info, I will be loading some of these up soon. 208's with A1680.

 

[Roadhawg]

Update:

I just got back from an additional test of some subsonic rounds.
The following is a 5 round average, they cycled the gun and had bolt hold open.

208gr Amax 2.220" 10.0gr 1680 1057fps

 

[FlatsFlite]

For noobs who might be considering loading subs, start on the high side of the data and work your way down. Pay close attention to proper function and squibs. A 900fps round for in my rifle may be a 0 fps round and in yours.

 

[Sticky]

For noobs who might be considering loading subs, start on the high side of the data and work your way down. Pay close attention to proper function and squibs. A 900fps round for in my rifle may be a 0 fps round and in yours.

Exactly! ^^^

Loading subs is bass ackwards.. start high and CAREFULLY work your way down, ensuring every boolit strikes the target. Leaving one stuck in your bbl is pretty catastrophic!

I load the 208gr Hornady to 10.5-10.7gr in a 10.5" pistol. 10.7gr is borderline subsonic, but very accurate in my pistol.

 

[Flipz]

I load the 208gr Hornady to 10.5-10.7gr in a 10.5" pistol. 10.7gr is borderline subsonic, but very accurate in my pistol.

Hornady 208gr BTHP with 10.7gr of 1680 @ 2.230 OAL. Very accurate and subsonic out of my Noveske 10.5".

 

[Speed3]

Hornady 208gr BTHP with 10.7gr of 1680 @ 2.230 OAL. Very accurate and subsonic out of my Noveske 10.5".

I have the exact barrel...I can't wait to load some of these

 

[deesly1]

Hey I have never went that low in grains with 1680 and 208gr AMAX. I have a 16" AAC 300 blackout upper with a 7.62sdn-6 can. I always used 11.3 gr. of A1680 to achieve a consistent, yet quiet, accurate shot at 100 yards. I also used 11.0 gr. of A1680 on a 220 sierra HPBTMK and it sounds like shooting a 22 lr. Another unique load I have used with the 208 gr. AMAX is Accurate No. 9 about 9.3 gr. very quiet but not accurate past 75 yards. I can give more detail about some of these loads if anyone is interested. Oh, I have a Spikes T-3 buffer in this particular rifle.

 

[BenL]

Exactly! ^^^

Loading subs is bass ackwards.. start high and CAREFULLY work your way down, ensuring every boolit strikes the target. Leaving one stuck in your bbl is pretty catastrophic!

I load the 208gr Hornady to 10.5-10.7gr in a 10.5" pistol. 10.7gr is borderline subsonic, but very accurate in my pistol.

That's about where I am: 10" barrel, 10.8gr 1680 give me ~1030fps.

 

[ironpony]

I'm getting very similar results. 10" LW.