300 Blackout Load Testing

[Sling10mm]

Took my 300 Blackout AR SBR out for some load testing weekend before last. It has an 8.5" barrel, and I was using a 762-SDN-6 with the subsonic loads.

Here are the results:

All loads used LC brass (mixed headstamps 2009 to 2011) and CCI #41 primers.

130 gr Speer JHP, 17.5 gr Accurate 5744, OAL 2.040+/-.005
Result: slightly flattened primers and split necks (didn't go beyond this starting load)

130 gr Speer JHP, 14.0 gr Accurate #9, OAL 2.040+/-.005
Result: slightly flattened primers and split necks (didn't go beyond this starting load)

125 gr Speer TNT JHP, 18.5 gr Accurate 5744, OAL 2.045+/-.005
Result: slightly flattened primers and split necks (didn't go beyond this starting load)

125 gr Speer TNT JHP, 14.5-16.0 gr Accurate #9, OAL 2.045+/-.005
Result: slightly flattened primers

125 gr SST, 18.5-20.0 gr Accurate 5744, OAL 2.105+/-.005
Result: slightly flattened primers and split necks at 19.5 gr (didn't try the 20.0 gr load)

125 gr SST, 14.5-16.0 gr Accurate #9, OAL 2.105+/-.005
Result: slightly flattened primers

208 gr A-MAX, 11.0 gr Accurate 5744, OAL 2.245+.005
Result: slightly flattened primers, still supersonic, would not cycle without the suppressor

208 gr A-MAX, 10.5-9.5 gr Accurate #9, OAL 2.245+/-.005
Result: slightly flattened primers and split necks at 10.5 gr (10.0 and 9.5 gr loads ok), still supersonic, 10.0 and 9.5 gr loads would not cycle without the suppressor

I'm not really concerned about the slight flattening of the primers, but not sure what to think of the split necks. Could it be because the necks aren't annealed? Still need to narrow the loads down and get out with the chronograph. I was getting decent accuracy with the Accurate #9 and SST bullet, so hopefully those are generating reasonable velocity. For the subs, the 9.5 grains of #9 was getting close to subsonic I think, and I need to try a reduced load of the 5744.

Still a lot of work to do, but I'm pretty happy so far.

 

[gopurdue02]

What is your case trim length?

 

[Sling10mm]

I believe it was 1.360+/-.003.

 

[Sling10mm]

Oh yeah, here's a picture of the gun. Kinda wish I had gone with an 8" barrel, but oh well.

 

[romack991]

What made you go with #9 and 5744? 1680 seems to be the most popular followed by H110 and Lil Gun.

 

[Sling10mm]

I already use those two powders, and there is load data available for them. Also, I wasn't having much luck finding 1680 and H110. I did see some of both of those powders at the 1500, so maybe they are becoming more available.

I'm going to stick with these two powders for now. The #9 showed some decent accuracy potential, and for subs the 5744 looked like it had room to go down still.

 

[jblomenberg16]

I've had very few, if any split necks on my 300BLK, and I'm not annealing anything.

 

[Bfish]

Oh yeah, here's a picture of the gun. Kinda wish I had gone with an 8" barrel, but oh well.

How long is your barrel?

 

[papa6x]

I use reformed Lake City blank, and .556 brass with my reloads and haven't had any problems. Then again I don't get close to the max loads either. I tend to stay in the mid load range.

 

[Dog1]

I'm using a 220gr bullet-Either Sierra or Blackout Bullets, cases trimmed to 1.358, Federal Match Primers and 7.7grs of Lilgun.

Subsonic, stupid quiet. No flatten primers or split necks. 8.2" CMMG barrel.

 

[Sling10mm]

How long is your barrel?

I used an 8.5" Bison Armory barrel. If I had gone 8" it would have eliminated that gap between the handguard and the suppressor, but it's no big deal.

As far as powder goes, I think the supersonic loads using the 5744 were just too hot resulting in the split necks. I'm going to try some reduced loads of 5744 for the subs, and some loads around 15.5 gr of #9 for the supers. That 15.5 gr load resulted in the best groups, so I'm going to test a couple of tenths of a grain on either side. Need to get the chrono out too and see what kind of velocities I'm getting.

Thanks for all of the advice on the other powders. If I find the 5744 and #9 aren't adequate I'll try to hunt some of those down, but I hate to add even more powder types to the inventory.

 

[Sling10mm]

Interesting thing….. I disassembled the rounds left over from the load testing. These were the remaining rounds where the starting loads were splitting cases, and are once fired brass (fired as 5.56mm) cut and reformed, so they haven't been fired as 300 Blackouts. After pulling the bullets and dumping the powder, I resized them. This was probably overkill, but I wanted the bullet tension to be consistent with the other brass I was using. About half of these cases ended up with split necks during the sizing process, specifically when the case was pulling off of the expander ball. The rest of them were reloaded without issue.

I'm going to try and get out to the range tomorrow, so I'll see if the neck spitting continues.

 

[CountryBoy19]

What made you go with #9 and 5744? 1680 seems to be the most popular followed by H110 and Lil Gun.

IIRC, H110 doesn't work well in the subs... and 1680 is VERY hard to find right now... I'm not the OP but I can tell you why I'm not using 1680; I've been watching all the popular places for months and can't find any mail-order/online, which leaves my only option as driving an hour, paying parking and entry fee to a gunshow, all in the HOPES of over-paying for powder. Nah, I'll leave that to other people...

 

[jblomenberg16]

H110 can work in subs but as you said it can be temperamental. I've had some luck with H4198 in some subsonic loads as well.

 

[romack991]

IIRC, H110 doesn't work well in the subs... and 1680 is VERY hard to find right now... I'm not the OP but I can tell you why I'm not using 1680; I've been watching all the popular places for months and can't find any mail-order/online, which leaves my only option as driving an hour, paying parking and entry fee to a gunshow, all in the HOPES of over-paying for powder. Nah, I'll leave that to other people...

1680 in stock now at powder valley. Both 1 and 8lb. Won't last long.

 

[Sling10mm]

This is kind of becoming more of a reloading thread, which is all good. Just a quick update: I went back out this past weekend to try more subsonic and supersonic loads. The subs worked fine, with the best load being the lightest (9.8 grains of 5744). The supers didn't work out as well. From my original load testing I got up to 16.0 gr of #9 with a 125 gr SST and didn't have any case splitting. At that time the 15.5 gr loading appeared to have the most accuracy potential, so I loaded up more at 15.3, 15.5, 15.7, and 15.9 gr for this trip. Two out of the first three rounds I fired (15.3 gr) blew the case head. These were loaded the same way as the original batch (brass, powder, primer, and OAL). The only difference that is obvious to me is the temperatures this past weekend were 15-20 degrees hotter than the first outing. Doesn't seem like that would make that big of a difference. Needless to say, I didn't shoot the hotter loads, and guess I need to go back to the beginning and research my supers a little bit more.

 

[Bfish]

1680 in stock now at powder valley. Both 1 and 8lb. Won't last long.

Is that a local place or an online retailer?

I am looking at just picking up some lil gun. I just picked up everything to load 300blk but powder.

 

[CountryBoy19]

1680 in stock now at powder valley. Both 1 and 8lb. Won't last long.

I caught that; I've been going to all the big places and checking their inventory daily and noticed it in-stock yesterday; I grabbed 4 jugs of 1680 and 2 jugs of other powder. They must have got a pretty big shipment because it's still in-stock this morning...

 

[padawan]

I use reformed Lake City blank, and .556 brass with my reloads and haven't had any problems. Then again I don't get close to the max loads either. I tend to stay in the mid load range.

Same here on brass. We are using W296 with mid loads and have had no primer-flattening or neck issues. Pretty consistent so far with about 2-300 down range with Sierra and Hornady 125gr.