300 Blackout Load Data & Results

Over the past 2 Saturdays I have chronoed some 300 AAC Blackout ammo. As you can see, both factory and my reloaded ammo.

The funny part is.......... it is Strike 2 for me with subsonic ammo (still too fast). 3 strikes and I am out.......

Since my SOTA upper is still not running 100%, I have not done any accuracy testing.



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Thought of trying trail boss?

I have some TB and will try later. The trick is cycling subsonic ammo.... From what I have read, AA1680 is the "best" for cycling subsonic ammo. I still have TB, LilGun and IMR 4227 to try for both sub & super.

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What length gas system?

I thought AAC recommended 10.8gr od AA1680 and a 220gr bullet. Remember with a can you will have more backpressure and better ejection than without it at subsonic loads
Oh and nice chart and good presentation of results. Cant tell you how much I appreciate organization

miker84 wrote:What length gas system?

Carbine.

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Don't remember where I found 11.2gr of AA1680. 10.8gr sounds like a good next try......

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BigDQ, like you, I have in the back of my mind the goal to get 175gr bullets subsonic and to cycle. This might be a Holy Grail..............

Another Holy Grail attempt...... 124gr to 2450.............. I can WISH....

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I've been trying to get 175 subs to cycle, but no luck yet. Thinking about trying a 200 just to see where the line is. I'm also curious to see what a short barrel does.

I think you're gonna need the 110 vMax to get to 2400.

My 175s cycle 99.9%
using A1680 at 9.9gr
Carbine gas system
With suppressor
I did open the gas port to .125 from .11 but I believe the issues I was having were related to my extractor being bad.
I ran it full auto this weekend with sub 175s without a hitch.

The can is the key. Gives more backpresseure through the gas port. Sub when mine gets here I am going to play with the 175s

I have tried them with no can and they seem to work but I haven't shot many without the can to say for certain. I also seat mine to 2.050 so they line up straight in the mags.

I am no "can expert", but I feel the added pressure from a can is super small. Yes, a can causes more gases back out the ejection port, but that is just the can bleeding off trapped pressure.

Crazy, is it hard to re-drill the gas port in the barrel? What about using a hand electric drill? Are special drill bits needed?

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If at all possible I would avoid it. I put a wooden dowel in the barrel to prevent going through and hitting the rifling. Then just use a drill press if available with a standard metal cutting drill bit. I will add that after drilling mine the barrel shaves jackets. I don't know if it's from the port or if I opened the port up into the rifling. Could be a burr but after looking at a recovered intact bullet it looks like I opened the gas port up to where it is on the edge of the rifling. I'm no professional so this is just my assumption. I do have some lapping compound to see if I can fix it but I haven't tried it yet. Like I said above it's the last thing I'd try. I went from .11 to .125 and now I get copper shaving coming into my bolt carrier from the gas port. I'm gonna do what I should have done and get a pistol length gas system since I only shoot subs. I didn't the first time around because I was impatient and everyone was out of pistol length barrels.

My thumbs hurt after that paragraph.

Crazy, MANY thanks on your heads-up about drilling a barrel. Not a job for me to attempt. Now go put your thumbs in some cold water..........

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Well, I finally gave in to temptation and drilled out my port. Ran 20 175 subsonics through it (with can) and they all cycled. My port was less than .08, opened to .10 (pistol-length gas)

At the M&G, it was having trouble cycling anything. The BCG was caked pretty good with carbon so I don't know if my loads are causing that or what. Running fine now after a good cleaning (imagine that). The extractor was certainly sticky when I got home from M&G.

The can is going to cause extra crud back through the BCG. Cleaning more often would be required. Glad to hear you got your 300BLK running again. Have not had a chance to work on mine......

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