300 blackout load help please?

[freakinhugebear]

I am having a heck of a time getting a subsonic load out of my 300 blackout. I have three 300blk AR's. Two are 16" one is 11" but I can't assemble that one until I get SBR paperwork back so I only have tested one of the 16" ones which is a CMMG 16" wasp barreled upper.

I am using the lee 230 grain mold and it's dropping 228gn consistently. I am using cci small rifle primers and converted brass. OAL 2.16 I think off the top of my head. I have tried it all the way down to 8 grains of 1680 and also 8 grains of lilgun. I'm still supersonic on both of those loads and I keep hearing people say that they shoot 10 grains of the 1680 on that boolit with a 16" and are still subsonic?? At 8 grains the bolt isn't even cycling and it's still supersonic. I don't know what the heck to do. I have not had a single load subsonic since I've had my can back and it's loud as heck. I'm real frustrated and could really use some pointers here. Thanks in advance!

[KYShooter73]

Let me guess...That CMMG barrel has a carbine length gas port, correct? I had the same barrel...it went back to midway and I purchased a barrel with a pistol length gas port. Everything was smooth sailing from there on. Rifle would cycle with much lighter loads. Your buffer and spring might also need a little tuning.

[freakinhugebear]

what charge were you using? I am more puzzled with the supersonic issue than I am with the cycling. I just loaded 7 grains of lilgun on that 230 and still super. What load did you end up with after you switched? I am thinking of going down to 6 grains and hopefully getting subsonic then working on getting a lighter buffer spring...

[TES]

welcome to the site bear.....Did I see you guys at the show this weekend?

[KYShooter73]

I do supersonics with 155gn, so other than the pistol port being more efficient with fast burning powders, we are comparing apples to oranges.

[freakinhugebear]

Thanks TES, not sure what show that might be but I was at the LGC USPSA match this weekend.

[freakinhugebear]

I do supersonics with 155gn, so other than the pistol port being more efficient with fast burning powders, we are comparing apples to oranges.

Ahhh I gotcha. This setup runs every super I've put through it so just an issue with subs.

[Moonie]

I doubt 8gr of AA1680 is supersonic with the Lee 230gr. How far away from your barrel is the crony? Too close and you could be picking up the powder/gas rather than the boolit.

[petroid]

I haven't used the same powders as you but I can get H110 to fully function with that bullet at 8.5 gr and about 950 fps. I also use Reloader 7 at 10.8 gr for about 1000 fps. I have a 12.5" CMMG 1:7 with pistol gas

[Smoke4320]

lee 309 230 5R powdercoated and sized .311 Noveski 10.3" (pistol gas port) and YHM Suppressor

9.3 Grains of RL7 gets me right at 1000 FPS totally quiet with a YHM suppressor .. most accurate of the 3 loads listed

9.8 Grns of H4198 gets me 750 FPS and full function

7.2 grns 2400 gets me 900 FPS Full function

[freakinhugebear]

I am not using a chrony, it is pretty darn easy to tell supersonic vs sub when using a can.... I finally got subsonic with 6 grains of lilgun but gun won't cycle. It is extracting but not picking up another round. I lightened the buffer and spring before shooting so I think it is very close to cycling but just needs a bit more gas...

[freakinhugebear]

also, I am sure the standard loads you all are talking about would work on my 11" sbr with pistol gas system, but it would seem on a 16" carbine gas system, this round is a completely different animal with subsonic loads. do any of you have 16" carbine experience with these subsonic loads?

[Moonie]

also, I am sure the standard loads you all are talking about would work on my 11" sbr with pistol gas system, but it would seem on a 16" carbine gas system, this round is a completely different animal with subsonic loads. do any of you have 16" carbine experience with these subsonic loads?

I have 2 of them, 16" with carbine length gas, with a chrony, I shoot subs all the time. Without a crony you really are only guessing.

[wlc]

I've got a 16 inch 8 twist in 300blk with carbine gas. I get subsonic with 10.2g of 1680, and I do use a can. In my rifle, 10.2g is questionable on the cycling but I haven't had time to go any further with the load development. I'm thinking that 10.3 will be good to go. I've also used RL7 (can't remember the load right now) at somewhere around 10g and it is subsonic as well. I think you are just hearing the bullet smack the target(???). 1680 is a "loud" powder compared to some of the other ones folks use in other than AR 300blk rifles. I have a load using green dot under some 180g bullets that is stupid quiet, but it won't think of cycling the action.

ETA: All my load work so far has been with jacketed, not cast. Waiting on that new ACE mold to get made before going down the cast rabbit hole with my blk.

[Jupiter7]

Without a chrony, this is all speculation. I'd re-check my scales too.

[lksmith]

Try bumping your charge to 10.5gr.
I have the same 16" CMMG set up as you and getting it to cycle with the suppressor and keep subsonic is tough.
The load that has worked for me is 10.5gr of H4198 which has a similar burn rate to AA1680 under a NOE 247 whisper running ~1050 fps.
When the gun is clean and lubed it will cycle and lock back without the suppressor and is pretty reliable.
I have the same Lee mold as you and with my limited testing appears to work almost as well as the NOE boolit.

I am thinking of opening up the gas port and changing to an adjustable gas block , should I decide to shoot supers in it again

[freakinhugebear]

Thanks for all the replies. I can double check with my friends chrony I guess but a supersonic crack is pretty distinctive especially with a can. I took the charge to 6.5 grains of lilgun and finally dropped the crack and it's stupid quiet, 7 grains is supersonic and still loud. At this charge it ejects the case but won't pick another one up. It's not my scale I have verified this with a balance scale and digital scale, I shot this 20 shot group with my 308 at 200 yards that same day so I doubt my reloading practices are the issue.

http://i60.tinypic.com/2uopac7.jpg

[xacex]

You may want to play with your buffer weight, and look to see if you are running a m16 carrier or AR15 carrier. I find for subsonic work with carbine gas I needed an AR 15 carrier with a lighter buffer to get full function. With the pistol port CMMG carbine barrel it is a non issue. I just had to add an adjustable gas block for supersonic. You can also increase your crimp to see if that helps before you go switching things up.

[freakinhugebear]

You may want to play with your buffer weight, and look to see if you are running a m16 carrier or AR15 carrier. I find for subsonic work with carbine gas I needed an AR 15 carrier with a lighter buffer to get full function. With the pistol port CMMG carbine barrel it is a non issue. I just had to add an adjustable gas block for supersonic. You can also increase your crimp to see if that helps before you go switching things up.

Thanks for the tips! I pulled a weight out of my buffer and have a lighter spring in, I also had the same thoughts about the bcg and verified it is an AR bolt as I have a lot of AR's and some have M16 bcg's in it. I think I am very close to having it right since it is consistently ejecting shells but just not picking another up... My local gunsmith said he can open the gas port up for $40, I'm thinking of doing that and putting the syrac ordinance adjustable gas block on. Any thoughts on that route? I've already got the spring as light as it can get, I may try taking more weight off the buffer but I think it's at it's lightest to consistently get in to battery.

[lksmith]

Thanks for the tips! I pulled a weight out of my buffer and have a lighter spring in, I also had the same thoughts about the bcg and verified it is an AR bolt as I have a lot of AR's and some have M16 bcg's in it. I think I am very close to having it right since it is consistently ejecting shells but just not picking another up... My local gunsmith said he can open the gas port up for $40, I'm thinking of doing that and putting the syrac ordinance adjustable gas block on. Any thoughts on that route? I've already got the spring as light as it can get, I may try taking more weight off the buffer but I think it's at it's lightest to consistently get in to battery.

Haven't tried the spring change on mine, but have tried the weight change by adding and subtracting the weights in the buffer from empty buffer to adding weights from another buffer to make it super heavy and didn't have any luck in my case.
I am looking at opening the gas port up to 1/8 (.125) to match the tube ID and allow me more flexibility in my load so I can tweak accuracy and get it quieter.

[xacex]

I think I read somewhere that the CMMG carbine/carbine gas barrels may have had undersized gas ports, but if your gun is new I would do some other things before you go that route. First I would run it good and wet with CLP with some supersonics to get the carbon built up around the gas port and gas rings to get it good and sealed, and broke in a little. Also, if you go below a certain level with powder space especially with these ball powders you can get a varying level of speed and it can actually increase a little. Enough for you to go supersonic. I went to 11.4 grains and was subsonic at sea level, but 11.8 went trans on me. With subs I work down with the powder charge instead of up. You already are below 35Kpsi at 9.5 grains, so there is no worry about over pressure, and you work down until you lose the supersonic crack, and it still functions. I would be worried with 8 grains sticking a squib in my pipe, but it sounds like from your experience you have no worry except for detonation. Btw, I would try the hodgdon recommendation of 9.5 grains, or 10 grains of h110, or 8.7 grains of lil gun and see if it slows down a bit with the decreases air space before doing something drastic.
300 Blackout, and Ar's are different cats and need to be dealt with a little differently than many other guns. Who would have thought to chop off a case, or resize a 221 fireball to accept a heavy for caliber projectile, and then use pistol power behind it? Oh, that right JD Jones...

Edit: Looking through your post it looks like you have worked down to 8. You need to get a chrony bro. I think you went sub a couple of grains ago. Inspect your can for a baffle strike something is not right with what you are hearing. FWI, some companies won't use a CMMG barrel for there builds because of bore contricity problems at the muzzle leading to baffle strikes. I sure hope for your sake that that is not the case.

[freakinhugebear]

you seem to be confusing transonic with supersonic. transonic is a projectile that goes supersonic and then slows to the point of subsonic (usually important when trying to shoot a 308 load at 750 yards + because going transonic can effect accuracy when the sound wave created by the previously supersonic round throws off the trajectory of the now subsonic projectile.) I think maybe just a typo on your end up there, but I figure i'd clarify just incase you weren't aware.

I have a huntertown kestrel, I have no baffle strikes as my can is easy to break down and I have cleaned and inspected it. Also a baffle strike would sound much more like muzzle noise than supersonic crack which will echo very distinctively. 7 grains of lilgun on my 228 grain projectile is supersonic, i know enough to be absolutely sure of that... the sonic crack is very distinct. 7 grains of lilgun is supersonic and does cycle, 6-6.5 grains is subsonic and does not cycle. anything under 8-9 grains of a1680 is supersonic and is nowhere near cycling. I seat the projectiles as long as I can get them and still work in a pmag. I think I'm going to go ahead and have the gas port opened up, I am confident that even slightly more gas would get this thing reliable.

[popper]

that adj block is good, been using it with cast ,308, and no problems. 0.125 is really big! ~40% of bore.

[xacex]

Nope, not confused. I list loads that can't make it to the target as indicated by slightly supersonic at the muzzle, and tipping at the target (50 yards) as transonic. But, I also am not using a can, so I can define it differently than you would. Those Huntertown arms cans look good for the price. How is the sound with factory subs? I am going a different way after a friend let me put his 308 can on my blackout. It is so quiet all you hear is action noise, and a little gas noise. The action is noisy by itself, and will never be as quiet as I like, but his can was a form 1 and quieter than some other factory cans I have heard at the club. He said I can follow his plans as soon as I get the paperwork done. It feels heavy tho. I just finished the paperwork for the trust, and have it ready for eforms to be back up for form ones.
Sounds like you have the right idea with opening up the gas port at this point. Mine on the carbine/carbine gas is .110 and runs 4 ways(confirmed) without an adjustable gas block. I do have an adjustable on my carbine/pistol gas and to be honest it makes it a pain to switch unless you are just shooting a particular load. It is nice to be able to use different powders but as the primary 300 blackout I would advise against it. You have a pistol build you are doing, and that would be best for shooting subs with a can anyway due to the length. I would be judicious with the carbine gas port so you can use it without adjusting it later.
Drilling the port slightly larger is no problem. Just use the proper size sharp bit, and do not go too deep, and go slow. Clean the bore real good, and any slight burs left will be gone after the first shot. A 7/64" bit should get you there without going over .110. that is .109375" before any diameter changes caused by chips ect. Do it on a press, and make sure you are lined up good in the vice.
We are kinda DIY out here, but if you are not confident by all means support your local smith. We have a great one right on this board. You can kill a barrel, and possibly yourself if you mess up the job.

[lksmith]

Nope, not confused. I list loads that can't make it to the target as indicated by slightly supersonic at the muzzle, and tipping at the target (50 yards) as transonic. But, I also am not using a can, so I can define it differently than you would. Those Huntertown arms cans look good for the price. How is the sound with factory subs? I am going a different way after a friend let me put his 308 can on my blackout. It is so quiet all you hear is action noise, and a little gas noise. The action is noisy by itself, and will never be as quiet as I like, but his can was a form 1 and quieter than some other factory cans I have heard at the club. He said I can follow his plans as soon as I get the paperwork done. It feels heavy tho. I just finished the paperwork for the trust, and have it ready for eforms to be back up for form ones.
Mine is HTG M30A and I like it. it is heavy but user serviceable and it sounds like a CO2 pistol using my load that has enough gas to cycle the action with a 16" bbl and Carbine gas system. I have it's little brother (Aris 4) for 22cal. Makes the 223 AR sound like a 22lr and on a 22lr with subs the bullet flying through the air is louder than the shot. The only difference (other than 22cal vs 30 cal) between the 2 are that the M30A has 1 more baffle than the Aris

[xacex]

Mine is HTG M30A and I like it. it is heavy but user serviceable and it sounds like a CO2 pistol using my load that has enough gas to cycle the action with a 16" bbl and Carbine gas system. I have it's little brother (Aris 4) for 22cal. Makes the 223 AR sound like a 22lr and on a 22lr with subs the bullet flying through the air is louder than the shot. The only difference (other than 22cal vs 30 cal) between the 2 are that the M30A has 1 more baffle than the Aris

The form one can I tried is about as quiet as that, maybe a little less. If the kestrel is heavy to the only advantage is user serviceability, but I can dip this one, and for the savings I might as well go that route. He has several thousand rounds through it of 308 so 300 blackout should be no problem. He said it was all S/S so it can handle dipping to get the crud out. He spent about 50$ in materials, and has less tools than I do so go figure. I could probably make it serviceable if I had a rotary table on the mill, and CNC set up. Right now I am still manual, and learning G code to find my way around this MACH3 program I have been playing with. I still got some time.

Hey, you hear about Doe Run?

[wlc]

Nope, not confused. I list loads that can't make it to the target as indicated by slightly supersonic at the muzzle, and tipping at the target (50 yards) as transonic. But, I also am not using a can, so I can define it differently than you would. Those Huntertown arms cans look good for the price. How is the sound with factory subs? I am going a different way after a friend let me put his 308 can on my blackout. It is so quiet all you hear is action noise, and a little gas noise. The action is noisy by itself, and will never be as quiet as I like, but his can was a form 1 and quieter than some other factory cans I have heard at the club. He said I can follow his plans as soon as I get the paperwork done. It feels heavy tho. I just finished the paperwork for the trust, and have it ready for eforms to be back up for form ones.
Sounds like you have the right idea with opening up the gas port at this point. Mine on the carbine/carbine gas is .110 and runs 4 ways(confirmed) without an adjustable gas block. I do have an adjustable on my carbine/pistol gas and to be honest it makes it a pain to switch unless you are just shooting a particular load. It is nice to be able to use different powders but as the primary 300 blackout I would advise against it. You have a pistol build you are doing, and that would be best for shooting subs with a can anyway due to the length. I would be judicious with the carbine gas port so you can use it without adjusting it later.
Drilling the port slightly larger is no problem. Just use the proper size sharp bit, and do not go too deep, and go slow. Clean the bore real good, and any slight burs left will be gone after the first shot. A 7/64" bit should get you there without going over .110. that is .109375" before any diameter changes caused by chips ect. Do it on a press, and make sure you are lined up good in the vice.
We are kinda DIY out here, but if you are not confident by all means support your local smith. We have a great one right on this board. You can kill a barrel, and possibly yourself if you mess up the job.

One thing I'll add to this, put a bore sized wooden dowel in the bore before you drill it out. It really adds nothing to the process, but gives you a buffer in case you get too carried away drilling and drop the bit through the hole and hit the other side of the barrel.

[lksmith]

The form one can I tried is about as quiet as that, maybe a little less. If the kestrel is heavy to the only advantage is user serviceability, but I can dip this one, and for the savings I might as well go that route. He has several thousand rounds through it of 308 so 300 blackout should be no problem. He said it was all S/S so it can handle dipping to get the crud out. He spent about 50$ in materials, and has less tools than I do so go figure. I could probably make it serviceable if I had a rotary table on the mill, and CNC set up. Right now I am still manual, and learning G code to find my way around this MACH3 program I have been playing with. I still got some time.

Hey, you hear about Doe Run?

On moth of mine they catch all or nearly all muzzle gases since I can hold it right over my chrony and it doesn't see the blast wave from the muzzle
M30A is almost all stainless with a stainless Cerakote tube. The only thin that isn't SS is the blast (first) baffle which is Inconel and Inconel generally stands up MUCH better than SS to heat and chemicals. I sold inconel to a chemical company that used it in some nasty stuff that would eat ss in short order. It would probably be quieter
if I didn't need so much gas to cycle my gun

If you can get a quet suppressor for $100 or less plus the unconstitutional $200 tax stamp you'd be crazy not to

You talking about them closing or something else happen?

[xacex]

If you can get a quet suppressor for $100 or less plus the unconstitutional $200 tax stamp you'd be crazy not to

You talking about them closing or something else happen?

No, it is a form 1 suppressor= DIY in my garage after the stamp comes in. His looks good for an all welded stainless. Bet I can do it better, but don't tell him that. His is 11 inches, but I bet I can take that down a couple and still have good suppression with 300 BO. I will put 11 on the form and go from there. May want to do it for full power 308 like his.

[KYShooter73]

Thanks for all the replies. I can double check with my friends chrony I guess but a supersonic crack is pretty distinctive especially with a can. I took the charge to 6.5 grains of lilgun and finally dropped the crack and it's stupid quiet, 7 grains is supersonic and still loud. At this charge it ejects the case but won't pick another one up. It's not my scale I have verified this with a balance scale and digital scale, I shot this 20 shot group with my 308 at 200 yards that same day so I doubt my reloading practices are the issue.

http://i60.tinypic.com/2uopac7.jpg

If you can shoot a 200 yard group like that I best drop out of this discussion as I have nothing to add. ( But I will add that I did bore out my CMMG carbine gas port which helped quite a bit.). ;-)

[lksmith]

If you can get a quet suppressor for $100 or less plus the unconstitutional $200 tax stamp you'd be crazy not to

You talking about them closing or something else happen?

No, it is a form 1 suppressor= DIY in my garage after the stamp comes in. His looks good for an all welded stainless. Bet I can do it better, but don't tell him that. His is 11 inches, but I bet I can take that down a couple and still have good suppression with 300 BO. I will put 11 on the form and go from there. May want to do it for full power 308 like his.
Do yourself a favor an go ahead an build it for full pressure and only cry once. You cb search the net an get. Lot of ideas on baffle designs, gettin it 11" or less shouldn't be too difficult. My m30a is 8.5oal
p