Subsonic 300 blackout cycling

Winterborn · Aug 25, 2013

Greetings,

As part of my eternal quest to find a subsonic load that will cycle my 300 blackout without a can, I finally got ahold of some AA1680 to try out.

My rifle specs:

1:9 twist AAC barrel, carbine length gas system
3 oz carbine buffer

I tried out two subsonic loads so far with this powder:

220gr Speer FMJBT round using 10.8gr of A1680. This load was very soft and quiet, if not all that accurate (about a 5" group at 100yds). I will tweak it down a bit to see if that improves the accuracy at all.

230gr Lead SPBT, cast from a Lee 300 AAC mold using wheel weight lead. Same powder load as above, and the rifle cycled just fine. No leading present after 20 test rounds (all I made up).

So far so good, seems to operate just fine using this powder at subsonic loads with heavy projectiles.

vwluv10338 · Aug 25, 2013

How do you like the Lee mold?

Winterborn · Aug 25, 2013

vwluv10338 said:
How do you like the Lee mold?

Its very nice, works well. Its my first with this small of an opening, so learning how to fill it right took a bit of experimentation. With this large of a bullet I wait a bit longer than I normally would to empty it, to ensure the lube grooves are sharply defined.

I tumble lube the bullets using LLA, and don't bother to size them. So far, so good. Looks like a very cheap way to shoot my rifle vs. buying 308 jacketed bullets for target practice.

I'm considering getting a lighter weight mold, perhaps a 150gr, to experiment with gas checks and supersonic loads. I'll probably try to use Lil Gun for that as I have much more of it.

Sticky · Aug 25, 2013

Thanks for the update Rich! I will be starting to load for the 300 here soon (as soon as I finish my build) and still yearning to learn all I can about loading for it. Not suppressed... yet... but that could well be in next year's plans..

peace · Aug 26, 2013

I thought subsonic cylcing in an AR platform came with the addition of a suppressor?

paxfish · Aug 26, 2013

Are you getting near 1 MOA with the second load? Just wondering if that is possible with .300 subs.

hvymax · Aug 26, 2013

Standard physics. It takes a certain amount of energy to cycle an action. E=mc2. You decrease the c you have to proportionately increase m. Heavy hard lead subs seem to be the ticket and if you cast them cheap to boot. Probably want to stick with jacketed for sonics though.

SWO Daddy · Aug 26, 2013

RichB said:
Greetings,

As part of my eternal quest to find a subsonic load that will cycle my 300 blackout without a can, I finally got ahold of some AA1680 to try out.

My rifle specs:

1:9 twist AAC barrel, carbine length gas system
3 oz carbine buffer

I tried out two subsonic loads so far with this powder:

220gr Speer FMJBT round using 10.8gr of A1680. This load was very soft and quiet, if not all that accurate (about a 5" group at 100yds). I will tweak it down a bit to see if that improves the accuracy at all.

230gr Lead SPBT, cast from a Lee 300 AAC mold using wheel weight lead. Same powder load as above, and the rifle cycled just fine. No leading present after 20 test rounds (all I made up).

So far so good, seems to operate just fine using this powder at subsonic loads with heavy projectiles.

Any concerns shooting cast lead through a can which (I assume) isn't serviceable?

BradMacc82 · Aug 26, 2013

paxfish said:
Are you getting near 1 MOA with the second load? Just wondering if that is possible with .300 subs.

MOA or better is possible on subsonics. It takes a bit more effort, for me anyways, but it can be done.

I lack the magnification to really stay on point with my current setup, but my sub loads thru a 700 in 300BLK running a Nightforce gave 3 sub-moa groups.

Winterborn · Aug 26, 2013

SWO Daddy said:
Any concerns shooting cast lead through a can which (I assume) isn't serviceable?

I cannot say for sure as I do not own a suppressor (yet) but I would hesitate myself until wiser heads prevail. Even if there is no vaporized lead in the muzzle gases (gas checked bullet, for example) the bullet lube does in fact vaporize and I would assume would coat the inside of the suppressor.

I would consult the manufacturer of the suppressor at a minimum.

BradMacc82 said:
MOA or better is possible on subsonics. It takes a bit more effort, for me anyways, but it can be done.

I lack the magnification to really stay on point with my current setup, but my sub loads thru a 700 in 300BLK running a Nightforce gave 3 sub-moa groups.

At what range were these results? My groups were around 8" at 100yds, or 8 moa. As I only fired 20 test rounds, and was more concerned with a)actually getting the rifle to cycle reliably and b) preventing leading in the barrel I was happy to simply hit paper.

I will begin to work some different loads to check accuracy from this point on.

With supersonics (150gr FMJSP) using Lil gun, I was getting around 1-2 MOA groups at 100yds.

Winterborn · Aug 26, 2013

peace said:
I thought subsonic cylcing in an AR platform came with the addition of a suppressor?

For the most part, and with most powders, this is correct.

There are a few features that through my research at 300aacblackout.com and other forums dedicated to the caliber that suggest ways to allow subsonics to cycle without a suppressor.

As I lack the funds to buy the suppressor I want, for now, I have tried to make this happen.

The first factor is the gas system. A pistol length gas system is much easier to get subs to cycle without a can due to the smaller length the gases travel: i.e. much more of the gas is funneled into the gas tube before the bullet leaves the barrel. With this system subs can cycle with virtually any powder used, such as H110 and Lil gun and IMR 4227.

Aside from a custom order, very few 16" or longer 300 AAC barrels are available with pistol length gas systems.

With a carbine gas system, only one powder has been found to be reliable in cycling subs without a can, and that is AA1680. From what I have been told, this is the same powder Remington uses in its factory subsonic loads.

http://www.midwayusa.com/product/85...0-grain-subsonic-open-tip-match-otm-box-of-20

Using AA1680 I was able to shoot 220gr projectiles at a calculated 1050 fps, based upon load data. I do not own a chrony (yet) but the projectiles were not breaking the sound barrier. The gun cycled great, and locked open the bolt after the last round.

The real reason I am so concerned with this project is the ability to shoot cast lead projectiles at subsonic velocities so a) I do not have to buy jacketed projectiles for target shooting (yes I am cheap bastage

) and b) shooting at subsonic velocities is much less likely to lead up my barrel and gas system. I don't really want to use gas checks at this time but I may consider buying a mold for a lighter bullet and using gas checks for mild supersonic loads in the future.

For right now, experimenting with subsonic loads is fun and enjoyable process. Very nice to be able to cast my own rifle boolits.

BradMacc82 · Aug 26, 2013

100 yards.

I believe BenL has gotten a few into the sub-moa as well. My loads thru that Rem 700 actually surprised me, I thought they'd be close to MOA, but they were under .8" at 100 yards, string of 5 rounds.

With supersonics, and admittedly butchering the fundamentals, I've gotten close to MOA on 110gr Vmax's and H110.

View attachment 95011

With more magnification and not chunking my breathing, I know for a fact that load would be sub-moa.

Deep Creek Rock · Aug 26, 2013

RichB said:
For the most part, and with most powders, this is correct.

There are a few features that through my research at 300aacblackout.com and other forums dedicated to the caliber that suggest ways to allow subsonics to cycle without a suppressor.

As I lack the funds to buy the suppressor I want, for now, I have tried to make this happen.

The first factor is the gas system. A pistol length gas system is much easier to get subs to cycle without a can due to the smaller length the gases travel: i.e. much more of the gas is funneled into the gas tube before the bullet leaves the barrel. With this system subs can cycle with virtually any powder used, such as H110 and Lil gun and IMR 4227.

Aside from a custom order, very few 16" or longer 300 AAC barrels are available with pistol length gas systems.

With a carbine gas system, only one powder has been found to be reliable in cycling subs without a can, and that is AA1680. From what I have been told, this is the same powder Remington uses in its factory subsonic loads.

http://www.midwayusa.com/product/85...0-grain-subsonic-open-tip-match-otm-box-of-20

Using AA1680 I was able to shoot 220gr projectiles at a calculated 1050 fps, based upon load data. I do not own a chrony (yet) but the projectiles were not breaking the sound barrier. The gun cycled great, and locked open the bolt after the last round.

The real reason I am so concerned with this project is the ability to shoot cast lead projectiles at subsonic velocities so a) I do not have to buy jacketed projectiles for target shooting (yes I am cheap bastage ) and b) shooting at subsonic velocities is much less likely to lead up my barrel and gas system. I don't really want to use gas checks at this time but I may consider buying a mold for a lighter bullet and using gas checks for mild supersonic loads in the future.

For right now, experimenting with subsonic loads is fun and enjoyable process. Very nice to be able to cast my own rifle boolits.

Id be curious to know how bad the gas ports get clogged up with repeated use of cast bullets in a gas impingement gun like an AR. My Lyman Cast Bullet Book/manual warns against using cast bullets in AR's.

I fire cast bullets in my Tommy Gun (not gas impingement) and the Cutts Compensator gets really built up with lead particles & burnt lube, that is not easy to get off. I literally have to pick it out -but it does come off in bits of crusty rocks. But the the smaller gas port in the comp get completely shut from build up. Id be curious to know how hard or easy it is to get that stuff out of the gas block and tube on an AR.

Winterborn · Aug 26, 2013

Deep Creek Rock said:
Id be curious to know how bad the gas ports get clogged up with repeated use of cast bullets in a gas impingement gun like an AR. My Lyman Cast Byullet Book/manual warns against using cast bullets in AR's.

I fire cast bullets in my Tommy Gun (not gas impingement) and the Cutts Compensator gets really built up with lead particles & burnt lube, that is not easy to get off. I literally have to pick it out -but it does come off in bits of crusty rocks. But the the smaller gas port in the comp get completely shut from build up. Id be curious to know how hard or easy it is to get that stuff out of the gas block and tube on an AR.

I will be monitoring my rifle closely for this buildup. Part of the reason I wish to keep it in the subsonic velocity range and, perhaps, go to gas checks if necessary. As of this time I am looking closely at the bore, and at the slightest evidence of leading I will be taking the gas block and tube out and checking for lead.

After 20 rounds, nothing so far. I have a few dozen more casted and lubed that I will load this week and hopefully get back out to the range to test. I will be tweaking my loads to try to shrink the groups.

wgttgw · Aug 26, 2013

I will let you guys know in a year or so. I am shooting the Lee 155-312 checked @ around 1950 fps. I have shot approx 300 without anything other than a patch down the barrel. Kind of my on torture test to disprove cast bullet myths ( if only to myself). I plan to shoot it till it won't cycle.

Winterborn · Aug 26, 2013

wgttgw said:
I will let you guys know in a year or so. I am shooting the Lee 155-312 checked @ around 1950 fps. I have shot approx 300 without anything other than a patch down the barrel. Kind of my on torture test to disprove cast bullet myths ( if only to myself). I plan to shoot it till it won't cycle.

Cool, I am highly interested in this as well. Question: do you size the boolits at all to .309 or just run them unsized?

wgttgw · Aug 26, 2013

I am sizing and seating checks in a Lee .309 die. The alloy is near WW but I can't say for sure. I was a large batch I smelted of unknown ingots and the properties seem similar to WW (truly maybe a little softer) So far I have only shot ones with copper Hornady checks. I have some sized with aluminum homemade checks which I am planning on running when I get them loaded up. I have tried one of my other 30 cal molds (it is a custom mold really meant for a 30-30) but could not get it to feed well. I pick up a Lee 309-150rf to see if I could get it to feed, but I have not tried it yet. The Lee 312-155 was designed with the SKS in mind, but it seems near perfect for the 300 blackout as well. I will be using this gun some for deer hunting this year and I would like to find a bullet with the largest flat point I can get to feed.

Winterborn · Aug 26, 2013

wgttgw said:
I am sizing and seating checks in a Lee .309 die. The alloy is near WW but I can't say for sure. I was a large batch I smelted of unknown ingots and the properties seem similar to WW (truly maybe a little softer) So far I have only shot ones with copper Hornady checks. I have some sized with aluminum homemade checks which I am planning on running when I get them loaded up. I have tried one of my other 30 cal molds (it is a custom mold really meant for a 30-30) but could not get it to feed well. I pick up a Lee 309-150rf to see if I could get it to feed, but I have not tried it yet. The Lee 312-155 was designed with the SKS in mind, but it seems near perfect for the 300 blackout as well. I will be using this gun some for deer hunting this year and I would like to find a bullet with the largest flat point I can get to feed.

I had some .30 round point bullets loaded into some 300 BLK cases given to me, they would not feed even with M4 feed ramps. Closest I've gotten are spire points, but they feed fine.

I have seen that 312 lee mold, but not purchased it. I will be following your efforts closely to see how it goes, as I'm interested in casting for supers as well if I can keep leading to a minimum.

peace · Aug 27, 2013

You guys really are cheap.

I guess its a time = money trade off for me. I'm going to load 155 scenars in my 300 BLK for supersonic and 208 Amaxs for sub.

Justler · Aug 27, 2013

So far i'm loading around 11.6gr of 1680 for my subs with the NOE 247gr mold, no gas checks. COAL is around 2.10. I need to shorten it a bit as the bullets aren't seating all the way due to the length of the bullet I believe.

When the bullets are the right length, cycling doesn't seem to be an issue.

I use a 9.5" CORE15 barrel with pistol gas system and standard carbine buffer.

Thought you guys might appreciate some info.

Subsonic 300 blackout cycling

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