300blk subsonic cast help

[dallasb]

Hey guys,

I picked up some 203gr .310 polymer coated cast bullets from palmetto projectiles. I just loaded some up today to try out and not sure if I'm doing something wrong or if it's normal. I'm seeing small yellow "stuff" being deposited in the barrel and on the end of the barrel. I also noticed a type of sludge that was built up on the outside of the case. Pics below.

Rifle is a 16" barrel, 1:7 twist, carbine gas

Load is 10.2gr AA1680, 2.075 OAL, cases are slightly belled to ensure no shaving, very light crimp (just enough to straighten out case). I forgot to add that the build up in the picture below is from 1 round.

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[Artful]

Was that with a suppressor on it?

[Motor]

That looks like un-burnt gun powder to me.

Motor

[Artful]

Yeah, that's what I suspect as well - If you have a suppressor mounted it forces the pressure to be bottled up and the gases will flow back making your brass really dirty (and your action), and it keeps the unburnt powder from being blown down range and deposits it inside you suppressor and on the crown.

[dallasb]

Was that with a suppressor on it?

Yes that is with a suppressor.

Is unburnt powder a common thing with suppressed ARs? Anything I should be concerned with?

[Motor]

Yes that is with a suppressor.

Is unburnt powder a common thing with suppressed ARs? Anything I should be concerned with?

I don't really know. Research as much data as you can. Maybe a different powder works much better and burns more completely.

I'm real interested in this myself because my brother just bought a 300 BO upper and wants to shoot cast sub-sonic boolits. It will not have a can though.

Motor

[dallasb]

Yeah, that's what I suspect as well - If you have a suppressor mounted it forces the pressure to be bottled up and the gases will flow back making your brass really dirty (and your action), and it keeps the unburnt powder from being blown down range and deposits it inside you suppressor and on the crown.

Thanks Artful and Motor. This is my first suppressor so wasn't really sure what to expect. All I know is I should have bought one a long time ago.

[reddog81]

I'd try more crimp, a cleaner burning/more efficient powder, or high pressure charge(assuming you aren't currently at a max charge). Some powders burn cleaner with higher pressures. That looks like a lot of unburnt powder for 1 round.

[dallasb]

I'd try more crimp, a cleaner burning/more efficient powder, or high pressure charge(assuming you aren't currently at a max charge). Some powders burn cleaner with higher pressures. That looks like a lot of unburnt powder for 1 round.

Ok I'll try a little more crimp. These are subsonic rounds so I started at supersonic and worked my way down.

[Gtek]

1680 seems to be the go to in this platform with the heavies. Questions in my mind- reformed .223, if not how many rounds through AAC case? Crimp? Spring back? This set up seems to really like as much crimp as you can get away with. I have seen first hand how the ES came way down the more crimp that was applied (AA1680), was not paying attention to dirty. Maybe a little annealing is in your future and minimal re-sizing, and experiment with crimp. Keep crimping until Boolit sizing occurs then back up one. Do not know where you live but 10.2 is in the park and probably still 50-100 under crack. If you are shooting across a Chrony you may find you can move .2/.4 and still find your joy. Small batches, one change at a time. Welcome to the fun/madness!

[Artful]

You have to remember that 1680 is a slow powder for a 300 blackout case, I use it myself and 5744 with 160 grain plinkers. You did good starting out super and working down to subsonic. Where is your gas port on your AR? (Rifle, Mid, Carbine, Pistol)
You should always crimp on self loading firearms, because you don't want a bullet jammed back into the case raising pressures and maybe destroying your firearm.

If you don't have a chronograph start saving up for one as it's very helpful for subsonic loading.

[dallasb]

You have to remember that 1680 is a slow powder for a 300 blackout case, I use it myself and 5744 with 160 grain plinkers. You did good starting out super and working down to subsonic. Where is your gas port on your AR? (Rifle, Mid, Carbine, Pistol)
You should always crimp on self loading firearms, because you don't want a bullet jammed back into the case raising pressures and maybe destroying your firearm.

If you don't have a chronograph start saving up for one as it's very helpful for subsonic loading.

Gas port is carbine length. I don't have a chronograph yet as I typically just listen for the supersonic crack. As far as crimping I haven't ever done it with FMJ with my auto loaders, however I do have crimp dies and a Dillon so it's not a big deal to start. Is there a general rule of thumb for how much to crimp a cast rifle bullet?

[geargnasher]

Carbine systems can be difficult to get functioning properly with subsonics UNLESS you have a can to provide extra backpressure to work the bolt. In order to make enough gas volume and pressure without pushing the bullet past the sound barrier, slow-for-cartridge powders have to be used (AA1680 down to about Reloder 7 burn rate), and these will not burn cleanly while keeping the bullets subsonic. A can makes this filth especially bad, but it goes with the territory. Supersonic loads with any bullet weight tend to be a lot cleaner if they are developed up to the pressure range where the powder begins to burn cleanly.

Should you be concerned about it? Yes and no. It won't damage anything, but it makes a mess and will eventually cause stoppages due to fouled bolt gas rings, locking recesses, gas tube and key plugging up, powder grime in the fire control group, and general muck in the action. Keep these areas cleaned out and you'll be fine. Get yourself some bolt recess mops and a quality carbon removal tool for your bolt carrier group. Also, your can will get filled with this filth too and will need to be cleaned periodically, it really helps if it's a design that can be taken apart.

Gear

[dallasb]

Carbine systems can be difficult to get functioning properly with subsonics UNLESS you have a can to provide extra backpressure to work the bolt. In order to make enough gas volume and pressure without pushing the bullet past the sound barrier, slow-for-cartridge powders have to be used (AA1680 down to about Reloder 7 burn rate), and these will not burn cleanly while keeping the bullets subsonic. A can makes this filth especially bad, but it goes with the territory. Supersonic loads with any bullet weight tend to be a lot cleaner if they are developed up to the pressure range where the powder begins to burn cleanly.

Should you be concerned about it? Yes and no. It won't damage anything, but it makes a mess and will eventually cause stoppages due to fouled bolt gas rings, locking recesses, gas tube and key plugging up, powder grime in the fire control group, and general muck in the action. Keep these areas cleaned out and you'll be fine. Get yourself some bolt recess mops and a quality carbon removal tool for your bolt carrier group. Also, your can will get filled with this filth too and will need to be cleaned periodically, it really helps if it's a design that can be taken apart.

Gear

Thanks Gear. Do you have a powder that would be more appropriate for the application? My can can be taken apart but I would like to keep as much out of it as possible.

[geargnasher]

I use Reloder 7 in all of mine because it is the only powder that will work with cast subsonics in all of the different AR gas systems and I want just ONE load. I'm really not sure if it will cycle your 203-grain bullets or not without the can, probably will WITH the can though. Had to drill my 16" carbine-length gas port to .120" to get it to work without a can, and that longer gas system is the limiting factor among my BLK rifles. The pistol-length systems can handle 210-grain cast bullets and powder as fast as H-110. Also, Reloder 7 doesn't leave that gritty, grainy, pepper-like grunge like 1680 and 5744 do, it leaves little yellow, flaky mummies in the bore and scattered through the receiver that are much easier to clean out and allow higher round-count between cleanings. IMR 4198 also works pretty well and is reasonably clean. Those last two only work my carbine-length system with 230-grain and heavier bullets, though. I'm using stock carbine buffer weights and springs, and full-auto-rated bolt carriers in everything which have one extra ounce of mass vs. typical semi-auto bolt carriers. The extra mass slightly compounds the problem of getting enough pressure to reliably lock the bolt back on the last shot, but sure helps lock the bolt closed when the chamber is heavily fouled.

Another note on Reloder 7: I get single-digit SD numbers at 1060 fps with soft cast bullets (11 BHN) and a medium roll crimp. Very consistent even at well-below ideal pressure for good powder burn. AA1680 was so inconsistent that at an average around 1050 fps I would get a supersonic crack every few shots, one time I got a triple-digit deviation. 1680 is the burn rate we need, but it doesn't perform well for me at all. IMR 4198 wasn't very consistent either, but lots better than 1680. I have but didn't try H4198.

You'll just have to do your own experimenting to see what will and won't work with your particular rifle. Most of the factory-assembled BLK uppers are meant to work with 208-220 grain subsonic factory ammo and 110-125 grain supersonic factory ammo equally well and interchangeably. When you switch to cast bullets (less engraving pressure than jacketed and doesn't get the powder burning as well) and/or are using lighter-than-normal subsonic bullet weights, you're going to have to figure a custom solution for your rifle. I highly recommend going to Nosler's load data website and looking at their 300 BLK subsonic data, it is VERY helpful for what you're trying to do and you can study trends with different powders and weights to get a better picture of bullet weight to powder burn rate ratios. The muzzle velocity numbers in the Nosler data for jacketed are very, very close to the numbers I get for same weight CAST bullets with same powders and charge weights, so don't worry that the data isn't for cast bullets.

Gear

[Jupiter7]

Yes that is with a suppressor.

Is unburnt powder a common thing with suppressed ARs? Anything I should be concerned with?

Totally normal. Nothing to see. Clean it up and carry on. Keep your bolt WELL lubed. All part of the subsonic and supressed game, especially in AR's.

[Moonie]

A firmer crimp will help powder burn. I also use RL-7 as I can't get Accurate powders locally.