What to do for 300 BLK subsonic

[Danimal]

New to the forum and new to 300BLK. I have a lot of experience with reloading and reloading for AR's and other semi auto weapons, but I have never reloaded subsonic rounds for a suppressed rifle. I would like to know a little about the process and what works best to work up a safe load. My current setup (though it will change when funds permit) is a 16" barrel with a 1 in 8 twist. It is a stainless Wilson combat I bought from midway on a standard A3 upper, auto BCG and carbine buffer standard milspec trigger group.

I am used to working up from the bottom to develop a load, but it seems that the process would be different for subsonic rounds. I have two options that I am thinking for projectiles and I would like some input as to what would be the best option.

Option 1) Run 180 grain bullets that I already have. I would love to shoot 220 SMK, but I am on a tight budget for the time being and I have thousands of 180 grain SPBT that I use for hunting with my bolt .308. I will never use that many for hunting or working up loads for that gun, so I might as well use them for this.

Option 2) Cast some 220 grain bullets. I do not have the molds or gas checks for this, but picking them up would not be a problem. I am not sure what alloy balance would be best if I am shooting them at about 1000 fps. Any input on that would be greatly appreciated as well.

[armed_zebra]

Finding a subsonic load is just the opposite of finding a supersonic load; you work your way down instead of working up. Reason being you don't want to start too low and end up with a bullet stuck in the bore. Also, I would suggest doing your load development WITHOUT the suppressor. You want to make sure the projectiles are stabilizing before you put them through the can. If shooting a semi auto such as an AR, you may have cycling issues without the back pressure from the suppressor. Just make sure you are getting nice round holes on paper before adding said suppressor.

As for your projectile selection, you may have some trouble with the 180's cycling. I know people have tried the 175's with little success. It seems as though they are not heavy enough to cycle the action in the ARs. Also, the round nose could give you feeding issues but I think the guys at Houston Armory got them to feed.

On a last note, I don't know that cast bullets through a sealed can is a good idea. I am not a caster but several here are and they might be able to give better advice on that.

[Danimal]

Thanks for the advice. I think that I am going to go with a can that I can open up and clean if need be. I am a little lost on which one that I should get. I think that I am going to start another post in the suppressor section and see where that gets me. I just don't know if it is worth getting a 9mm and a thread converter so I can use it on my pistols too, or just get a solid .30 cal one that is good for .308 and use it on my .308 from time to time. Either way I want to be able to take it apart and clean and inspect it, especially if I am shooting cast boolits through her.

[armed_zebra]

If you plan to shoot the cast bullets through it, then the user serviceable (take apart) can is the way to go. The only take down can I have is my 22 Silencerco Sparrow and I don't know what I would do if I couldn't take it apart. The molten lead builds up and will eventually render the can useless if it isn't cleaned. If NOT shooting cast bullets in a centerfire rifle, I don't see the need to be able to take it apart.

[jason]

I shoot 175gr subsonic bullets through my 16" AR rifle and 9" AR pistol. I have never had a cycling issue (with the suppressor on).
With the 16" barrel, I break the sound barrier with about 10.4gr of Accurate 1680. With the 9" barrel it's still subsonic with 10.8gr.
The lowest powder charge I've tried is 10.0gr, and it still cycles flawlessly. I have a standard pistol gas & buffer system, RRA upper and LMT BCG, if that matters.

[Danimal]

I shoot 175gr subsonic bullets through my 16" AR rifle and 9" AR pistol. I have never had a cycling issue (with the suppressor on).
With the 16" barrel, I break the sound barrier with about 10.4gr of Accurate 1680. With the 9" barrel it's still subsonic with 10.8gr.
The lowest powder charge I've tried is 10.0gr, and it still cycles flawlessly. I have a standard pistol gas & buffer system, RRA upper and LMT BCG, if that matters.

That is good to hear. It may still not work for me because the barrel I ordered is carbine length gas block. I have also read a couple other threads on here that talk about clipping back the buffer spring and using plastic or super light weight buffers so that they could shoot lighter weight projectiles subsonic. I guess I will just have to wait and see how my upper does when I am finished building it.

[jason]

That is good to hear. It may still not work for me because the barrel I ordered is carbine length gas block. I have also read a couple other threads on here that talk about clipping back the buffer spring and using plastic or super light weight buffers so that they could shoot lighter weight projectiles subsonic. I guess I will just have to wait and see how my upper does when I am finished building it.

My 16" is a carbine length gas system and it cycles with the 175s. It's worth trying. An interesting note: neither gun locks back with the CMMG 175gr subsonic factory rounds. I think my handloads are hotter.
I would recommend against shortening springs and going with a super light buffer, because you need that force and mass to get the bolt back in to battery. Also, if you try to shoot supersonics, you might bottom out the spring. Tweak the ammo to fit the gun.

[Danimal]

My 16" is a carbine length gas system and it cycles with the 175s. It's worth trying. An interesting note: neither gun locks back with the CMMG 175gr subsonic factory rounds. I think my handloads are hotter.
I would recommend against shortening springs and going with a super light buffer, because you need that force and mass to get the bolt back in to battery. Also, if you try to shoot supersonics, you might bottom out the spring. Tweak the ammo to fit the gun.

That is probably a better way to go. I just want it to cycle smoothly and still be subsonic with good effect down range. I think I will cook up some 180's tonight and see how they do. Although I don't know where I'll go shoot them because everywhere is on fire with no shooting allowed. Damn Colorado.

[JohnInNH]

I have not had much luck with 175, 180, or 190 (lead) subs running with a can on my PSA16" upper

Maybe its worth another try now that its hot out.

I just loaded 200 208 gr A-Max bullets 10.8 gr A1680 they run. I got a Lee mold and will try those in the AR. They may be the answer.

[Danimal]

I have not had much luck with 175, 180, or 190 (lead) subs running with a can on my PSA16" upper

Maybe its worth another try now that its hot out.

I just loaded 200 208 gr A-Max bullets 10.8 gr A1680 they run. I got a Lee mold and will try those in the AR. They may be the answer.

I just got a pretty good deal on 208 grain a-max bullets, so I bought 1000 of them. Hopefully it is the ticket, but I could not justify paying over double for SMK's. I finally got my upper assembled and when the fire ban gets lifted I will be working up a load. I ended up with AA No.9 as the first powder that I am going to try. It looks like it has similar pressures and burn rate as compared to Viht N-110, which I have been told is the best all around powder for subsonic blk (very reliable and qualified source). But again I could not jump on powder that is $13 more per pound. So I am going to see what I can come up with using these components.

Is the Lee mold that you have the tumble lube one? I really want to cast bullets for this platform but I have never cast rifle bullets before so I am hesitant. I have been working on casting for pistol for a while now, and I have had great success, but I hear that rifle is a whole different animal. Any thoughts or advice?