300 AAC Blackout 9" 220SMK sub load data - UPDATE

[nortac]

I have been doing my research and was curious what others are doing. I am using the following components.

9" AAC Blackout upper
220SMK Bullets
AA1680 Powder
Cut and resized Lake City Brass
Winchester WSR Primers

I have read that 11.2 grains of 1680 is good for subsonic on a 16" barrel. I have also read that people using 8" to 10" barrels are using anywhere from 9.0gr to 12gr to get ~1025fps. I am assuming I would need to load a bit higher than 11.2gr to achieve ~1025fps out of a 9" barrel but not sure with all the inconsistent data out there.

So for all you 9" AAC guys, what are you using?

 

[RBros]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

I run 11.3gr AA 1680 in my 10" Rock barrel. Is right at 1000fps, but its extremely accurate so I leave it alone.

 

[country888]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

I run 10.6 in my 8" satern & 16" noveske with 208 amax. 16" 1050fps. 8" 1020fps. Im not losing much with with 8"s less.

 

[redbullitt]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

I run a 10 inch barrel. I have run it down to 10g 1680. Velocity was reading quite low (Temperamental f1 chrony), but the rifle functioned clear down to there. Reading was 800 fps, and on the higher end of 11.5 I was getting mid 1000s. Neither load cracked AND pretty much everything cycled find.

Accuracy seemed decent, but i did not shoot at paper or anything like that to get a definitive reading. SD on the F1 was very satisfactory on the 11.0-11.5g loads.

 

[jkonzal]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

With my 16" barrel, I started with the 11.2 gr load, but ended up finding far better accuracy at 10.5 gr's.

 

[BRDTX]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

How many fps do you need to stabilize a 220 or 208 with a 1/8 barrel?

 

[country888]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

Not sure what the least you would need to stabilize the bullet, but most of us try to get then right at 1050 fps.

 

[j-huskey]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

Remington ammo tested in both 16" and 8.5" uppers. Remington subsonics are supersonic.
Hornady Whisper ammo subsonics are subsonic in both systems.

In Reloading, supersonic loads, H110 or N110. Either works well when you know the powder response to temperature.

AA1680 works fine with subs in the 208-220 weight range. This is with both the 16" AAC built upper and a 8.5" upper. Had to drop the charge in the 16" from what ran best in the 8.5, and I saw a post above that mirrors my experience.
DID NOT work with 240's in the 16" upper. Will cycle action to pick up next round but will not lock the bolt back. I was dissapointed in this. I wanted to be able to use the same buffer with all loads.


Anybody out there done a successful 240 load on a factory AAC gas set-up? Looking for assistance here.

 

[rsilvers]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: nortac</div><div class="ubbcode-body">I have read that 11.2 grains of 1680 is good for subsonic on a 16" barrel.</div></div>

That sounds like too much. That is a starting load. You have to start with that, and then adjust down to the actual load. Most people end up around 10.5, but you should always begin with a starting load and work down to avoid a stuck bullet.

 

[nortac]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rsilvers</div><div class="ubbcode-body">That sounds like too much. That is a starting load. You have to start with that, and then adjust down to the actual load. Most people end up around 10.5, but you should always begin with a starting load and work down to avoid a stuck bullet.
</div></div>

Well I agree with you now. I honestly figured I would need slightly more than the 11.2 out of a 9" barrel. Obviously I was wrong. I did a little shooting today and results are below. Based on this I think 10.8 to 11.0 will probably be where I need it to be.

9" AAC Blackout
Suppressed
AA1680
220SMK's
Cut and sized Lake City Brass
Winchester Primers
~500 ft above sea level
80F - 55% Humidity

11.3gr---11.5gr---11.6gr---11.7gr
1052-----1102-----1104-----1128
1082-----1092-----1104-----1097
1077-----1108-----1123-----1142
1077-----1101-----1098-----1128
1085-----1103-----1120-----1119

Anyone had issues with the brass being dented upon ejection?

 

[The Gump]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

Mind does them same thing. I'm not concerned with it.

 

[jkonzal]

Re: 300 AAC Blackout 9" 220SMK subsonic load data

Every single one of mine dents the same way. I think its from the way the brass ejects from the rifle. It will straighten out just fine when you re-size it.