Building a 300 Blackout?

[Dolomite_supafly]

I see there is a lot of interest as of late in the 300 Blackout. And it seems like there are a lot of people planning on building one in the near future so I figured I would post up some things to take into consideration when building a 300 Blackout. The two biggest considerations are what gas system and what twist.
 
First, let me start by saying that other than the barrels and muzzle devices all other parts are identical to what is found on any 5.56 AR-15. The lowers are identical and you should be able to use any standard lower that functions with a 5.56 upper with a 300 Blackout upper. A threaded 300 Blackout barrel will use 5/8-24 threads. That is the standard for any .308 caliber muzzle device.
  
What gas system do I need?
 
There are two types of gas systems used in the 300 Blackout, pistol length and carbine length. Each one has its own advantages and disadvantages, depending on how you look at it.
 
A carbine length gas system does not require an adjustable gas block and requires no adjustment if shooting supersonics. You can use a standard gas block which is a little cheaper than and adjustable one. But with a carbine length gas system you may run into problems cycling if you are not shooting supersonic, full power loads. I know I have read, and helped, a lot of people with carbine length gas systems and in 90% of the cases it requires a lot of custom parts to get it to function when shooting subsonic ammunition, even factory subsonic ammunition. Now if you are going to be adding a suppressor then the cycling issues go away in most cases. With a carbine length gas system you cannot shorten the barrel too much below 16" without running into cycling issues both with and without a suppressor. If all you ever plan on doing is shooting supersonic ammo then the carbine length gas system will work great. If you reload then the carbine length gas system can be finicky as far as what powders and bullet weights can be used.
  
A pistol length gas system may require an adjustable gas block, depending on port size, with a 16" barrel to shoot both supersonic ammo and subsonic ammo. A pistol length gas system setup to shoot subsonics may be over gassed when shooting supersonic ammo without an adjustable gas block but in most cases the gun will still be reliable but run a little dirtier. A pistol length gas system will be reliable with subsonics even if you do not have a suppressor. A pistol length gas system allows you to use the widest variety of powders and bullet weights. It also allows you to make a SBR or pistol with a barrel length down to as short as 7". The most reliable setup is going to be the pistol length gas system whether shooting subsonics or supersonics.
  
So in the end if you plan on shooting subsonics you want to have a pistol length gas system. If all you are going to be shooting is supersonics then a carbine length gas system is going to work fine. But a pistol length gas system will work with both but might require an adjustable gas block. You should be running an adjustable gas block anyways to tune the gun for reduced recoil, reliability as well as to keep it cleaner for longer. Using an adjustable gas block you can artificially lengthen a pistol length gas system but there is no way to artificially shorten a carbine gas system.
 
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Reloading for the 300 Blackout
For reloaders. There is tons of published data out there for both supersonic and subsonic loads. But you can also use load data for the 300 Whisper, which has been around for several decades. The two rounds are interchangeable.
 
As far as dies go any should work but I have seen some issues as of late with Lee dies. Personally I like the RCBS dies because I can replace the expander ball. It is important for me because I cast and with the .311" expander ball I do not size my cast bullets down as I seat them into the case.   

For those of us that cast or plan to. Be mindful that not all 30 caliber cast bullets will work with the 300 Blackout in an AR. Some require the OAL to be 2.26" to avoid exposing the lube grooves. And when you seat ANY bullet, cast or jacketed, to that length it can cause problems with some magazines. The ideal length should be under 2.15". Also, when loading cast bullets the case necks need to be larger than what you would use for jacketed. Also, if shooting cast you must bell the cast mouth. Lee makes a universal case mouth expanding die. And you want just enough of a bell to not shave the cast bullet. You should not be able to easily see or feel the bell. 
 
So how or where do I get brass?
You can either buy it or make your own. Buying it is self explanatory but because the caliber is based on a necked up 223 you can use 223 or 5.56 brass to make your own. You cut the 223 case off at the shoulder. Then you size and trim like any other caliber out there. To cut my brass I use a Harbor Freight mini chop saw and a fixture that holds the cases but you could use anything really. And even though it is a small case it still requires lube just like the 223.
 
 
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What twist do I need?
Twist rates. Barrels can be had in 10, 8, 7 and now 6.5. If you plan on shooting supersonics then any of them will work but if you are going to be shooting subsonics then you must take the twist rate into consideration. The numbers below are generalizations and you must test to verify. 
 
A 10 twist will stabilize most jacketed bullets up to 200 grain and most cast bullets up to 220 grains at 1,050 fps.
 
An 8 twist will stabilize most jacketed bullets up to 220 grain bullets and most cast bullets up to 250 grains at 1,050 fps.
 
A 7 twist will stabilize most jacketed bullets up to 240 grains and most cast bullets 250+ grains at 1,050 fps.
 
And the 6.5 twist is out there because there are rumors of a 260 grain Hornady Amax soon to be released.
  
With that being said you MUST verify your individual gun to ensure it is stabilizing the bullets. Shooting an unstable bullet will not harm anything unless you have a suppressor. To test shoot at a target 100 yards away without the suppressor on. Inspect the bullet hole in the target. It should be round and all edges look uniform. If the hold is oblong or has one edge that seems a more feathered than the other then the bullet is not stable.  If you find your load is NOT stabilized you either need to go to a lighter bullet or a faster velocity. Some 8 twist guns will stabilize 240 grain bullets and some won't so you MUST verify, especially if you are using a suppressor. I have a 10 twist gun that stablizes 245 grain cast bullets but I have had others that would not.

 

 

 

 

If anyone has any questions feel free to ask. I am sure I am missing a few things here. And remember the only dumb question is the one not asked.
 
 
 
 
 
 

Edited October 15, 2013 by Dolomite_supafly

[WindHawk]

Thanks, Dolomite that's great info.  I'm seriously thinking about 300 Black when I get my TGO lower/upper and this covers a lot of questions.  

[TMF]

I'm considering buying a .300 barrel and swapping back and forth on my primary AR for deer season. I'm not planning on hunting until next season though. My biggest concern is the ammo. It seems like the ammo is pricy to shoot a lot unless you reload for it. I'm curious what the estimated cost would be to get a beginner's level setup to start reloading .300, minus bullets, primers and powder.

[TripleDigitRide]

A 7 twist won't stabilize cast bullets?

[Dolomite_supafly]

A 7 twist won't stabilize cast bullets?

It will stablize any cast bullet out there.

[Dolomite_supafly]

A 7 twist won't stabilize cast bullets?

It will stablize any cast bullet out there. I edited it with some changes.

[Dolomite_supafly]

I'm considering buying a .300 barrel and swapping back and forth on my primary AR for deer season. I'm not planning on hunting until next season though. My biggest concern is the ammo. It seems like the ammo is pricy to shoot a lot unless you reload for it. I'm curious what the estimated cost would be to get a beginner's level setup to start reloading .300, minus bullets, primers and powder.

 

Just 300 Blackout for now? I bet you could go really, really cheap and get a setup under $150. Send me a PM to remind me and I will look around and work up a list.

[mikegideon]

G,

 

Regarding Lee dies. My loads work fine with Lee dies and a chamber that was reamed to Blackout spec. I think we discussed this the last time we were on the phone. Don't you have a barrel that's reamed to Whisper specs? I haven't had a chance to dig, but do know that the Whisper was a wildcat, and specs varied a little. That's probably the main reason AAC was able to make a "new" SAAMI caliber out of such an old wildcat.

 

I don't have the data to debate it, so I'm just going to say that the Lee dies seem to match up just fine with a true Blackout chambered barrel. 

[MacGyver]

I use Lee dies, but I'm not using much cast stuff, yet.  I'm going to let Gordon and Caster do all the beta work and then benefit from their experience :)

 

I've not had any issue with jacketed stuff. 

[mikegideon]

I use Lee dies, but I'm not using much cast stuff, yet.  I'm going to let Gordon and Caster do all the beta work and then benefit from their experience :)

 

I've not had any issue with jacketed stuff. 

 

I'm waiting until they come out with orange bullets. No drab colors for me :)

[nightrunner]

Regarding barrel twists, will the 7 or 6.5 twist also stabilize the lightweight bullets as supersonic speeds? How lightweight of a bullet can be used?

[E4 No More]

I'm waiting until they come out with orange bullets. No drab colors for me :)

Says the guy who had his chamber reamed! :)

[mikegideon]

Says the guy who had his chamber reamed! :)

 

Mine came reamed. That would be Dolomite :)

[TripleDigitRide]

Mine came reamed. That would be Dolomite :)

Can you expound on the reamed chamber? Why is there a need for this?

[Dolomite_supafly]

I have had several people here, maybe they will chime in, that have HIGH END guns and when they used Lee dies that I recommended the ammo would not chamber. And when they went to RCBS and Hornady dies the issue went away. These are not me but someone else. I do have a Whisper chambered gun and Lee loads will not chamber but RCBS loads will.

 

Daniel Defense is one of the ones I have seen have issues with Lee dies and fixed with other brands of dies.

 

I, for a long time, was singing praises of the 300 Blackout Lee dies but now that I have personally seen several guns have issues I am starting to change my mind. On another board there are a lot of people who are experiencing the same thing. At any rate if you have a 300 Blackout gun that doesn't want to chamber your rounds made with Lee dies look at the dies before you look at the gun.

[Dolomite_supafly]

Can you expound on the reamed chamber? Why is there a need for this?

 

There is no need to do this.

[Lumber_Jack]

Regarding barrel twists, will the 7 or 6.5 twist also stabilize the lightweight bullets as supersonic speeds? How lightweight of a bullet can be used?

I believe Robert Silvers did tests on twist rates as fast a 1:4.5" without problems. I don't think the .300 pushes the bullet fast enough to cause separation. However if you try to shoot long range (300yds) you may see failure of the bullet to "nose down" do to the too fast twist; this is all hypothetical though as I don't think it has been tested.

[mikegideon]

Can you expound on the reamed chamber? Why is there a need for this?

 

All chambers are reamed. That's how they make chambers in barrel blanks. Dolomite bought a blank, and had it chambered with a Whisper reamer.

 

I was wrong. See Dolomite's post coming up.

Edited October 15, 2013 by mikegideon

[TripleDigitRide]

All chambers are reamed. That's how they make chambers in barrel blanks. Dolomite bought a blank, and had it chambered with a Whisper reamer.

Ah, I thought you possibly had it reamed even more. Got it.

[mikegideon]

I have had several people here, maybe they will chime in, that have HIGH END guns and when they used Lee dies that I recommended the ammo would not chamber. And when they went to RCBS and Hornady dies the issue went away. These are not me but someone else. I do have a Whisper chambered gun and Lee loads will not chamber but RCBS loads will.

 

Daniel Defense is one of the ones I have seen have issues with Lee dies and fixed with other brands of dies.

 

I, for a long time, was singing praises of the 300 Blackout Lee dies but now that I have personally seen several guns have issues I am starting to change my mind. On another board there are a lot of people who are experiencing the same thing. At any rate if you have a 300 Blackout gun that doesn't want to chamber your rounds made with Lee dies look at the dies before you look at the gun.

 

When I get a chance, I'll grab my micrometer and compare my loads to factory loads, and to the blk spec. I have a cheesey barrel, so it may just be cut loose. I won't be able to measure the necks on fired brass, because my rifle dings the necks on the brass deflector.

[Dolomite_supafly]

I did not buy a blank and have it reamed. I bought a Contender barrel that was chambered as a Whisper. All my other guns were reamed using a Blackout reamer.

Edited October 15, 2013 by Dolomite_supafly

[mikegideon]

I did not buy a blank and have it reamed. I bought a Contender barrel that was chambered as a Whisper. All my other guns were reamed using a Blackout reamer.

 

That's what you get for talking to an old senile guy on the phone :). I'll edit my post

[Dolomite_supafly]

All the blanks I have used have been reamed using a Blackout reamer. The only Whisper I own I bought that way and did not build it.

 

This wasn't mean to start a Whisper vs Blackout discussion. In properly made guns, using ammunition made using properly made dies they should interchange. You should be able to shoot Whisper ammo in a Blackout gun and Blackout ammo in a Whisper gun.

[mikegideon]

The outside neck diameter of the Blackout is like .004 larger than the whisper. I think I read that it was done so you could neck down military brass. That's enough to make for some possible stickiness in a whisper chamber. The case length is .013 longer, be that has nothing to do with dies. 

[Dolomite_supafly]

Here is the chamber comparison of the Whisper and the Blackout:

 

The Blackout chamber is a little looser than the Whisper but the ammunition is the same. Think of it like 5.56 vs 223. I tell people that my Whisper is actually a Blackout "match" chamber.

 

Here is the dimensional drawings for ammunition according to Sierra. (notice they are identical except the max length of the case mouth is longer) And as long as the length is not at the max length of 1.368", which it shouldn't be, the 300 Blackout ammo should chamber in a 300 Whisper chamber. The ammunition will be tighter in a Whisper chamber but it should chamber just fine providing the ammunition is the same specs as specified below. But as I said I believe the problem with some Lee dies is they do not size the case down enough in the waist.

I think the .344" neck OD on the Whisper drawing is a error. I know my Whisper barrel has a .335" neck and all of my loaded ammo runs ~.332" +/- .001".