I had weighed them before.

A 77gr SMK (IMI) and a 110gr Hornady V-max were just about the same weight on my kitchen scale.  110gr Tac-tx was a hair heavier, but not much.   I may have to go back and re-record how much their exact weight.

But remember the key is that you don't need much barrel length for 300blk, so the benefit of bufferless uppers is more appealing for something you might keep on you or up front in a vehicle.

The 300BO is of course a very useful cartridge,

I am quite fearful of the potential risk.

I have chosen not to mess with it to the extent that I don't want to mess with it and won't  set up alongside someone else shooting it at my clubs range .

You would think it would be fairly easy to guard against getting the wrong ammo in a 5.56 but this type of thing is all too common.

Fair number of AR shooters at my club and many of them also have 300BO . No kabooms at my club to my knowledge but it scares me.

Glad the OP of this thread got no injuries and stepped up with his trials as a warning.

When I see someone at my club shooting 300BO I will ask if they understand the potential for kaboom problems but how the deal with it is up to them .

I do it my way but other guys are on their own to decide what they choose.

The day that 9x19 is able to throw 220gr projectiles with a BC north of .6 (and superior sectional density) is the day I’ll concede that 9x19 is superior for subsonic applications

 Is your kitchen scale graduated in grains?

You can relax the next time you see someone shooting a .300 Blackout.  Nobody's going to blow up their .300 Blackout gun.

You should worry anytime you see someone shooting a .223 or 5.56x45mm gun, THOSE are the guns that blow up & spritz parts all over the place, and they might not even shoot .300 Blackout.  Their buddy might have helped em at a mag loading session one evening and one round slipped into a mag.

Let us know what cartridge is superior in terminal ballistics.

was it a 10.5"?

chat sales asshole said they only sold nfa items to ffl.  

I literally had the entire sale setup and they refused to sell it to me.  

fuck that.  Blackstone 6.8 spc will happen instead.

The closest apples to apples comparison I can come up with off the top of my head is 147gr FMJ 9x19 and 150gr FMJ 300blk.

I’ll take the terminal ballistics of the 300blk, please and thanks

That is why I do not own a .300 Blackout!

Having said that... I kaboomed a 5.56 build.

I only shoot factory ammo in everything except 9mm ARs.

It was a Bear Creek Arsenal barrel and I forget who made the bolt carrier and bolt but was from a site that carries quality parts..

My first mistake was not doing my homework on BCA quality control.

The second mistake was not checking the headspace... the only time in a dozen builds!

Results were about the same but the lower survived... the upper not so much.

BCA replaced the entire upper half of the rifle, no questions asked (other than returned the damaged upper).

The first thing I did was check the headspace!!!

Attached File

Attached File

...and worst of all I lost a vintage GI 20 round magazine!
Attached File

Headspace blew up your AR?   Intersting - typically GI runs very long headspace.  And a headspace excess generally just results in a broken shell, where the .380/9mm sized back swells and seals anyway.  What ammo were you running?  First shot?  Were you getting broken shells or incipient head separation prior to kaboom?  

Too short headspace generally means bolt won't close, pin won't reach, and just *click*.  (Done that with insufficiantly sized brass way more times than I care to admit).

Not to hijack this one, but was there a thread on this?  I ask because I have a doubt headspace issue is what did that - and would like to know more - especially if that will correct an error in opinion on my part.

I'll post the pics tomorrow or Monday. It is late, and it took me awhile to find my 5.56 ammo, that is how long it has been since I shot it.  


77gr IMI SMK - 13gr - 0.45oz
110gr Hornady V-Max - 14gr/0.50oz

Remember, this is the weight of the entire cartridge, not just the bullet.  The projectile is heavier, but there is less brass and less powder overall for each round.  

As far as subs go, I think it is easier and cheaper to find good expanding 9mm subs (147 HST) vs the "good" 300blk rounds.  (Maker Rex or Lehigh Maximum Expansion).  The Makers are basically impossible to find pre-loaded, and the Lehighs cost both arms and both legs.  Hornady 190gr Sub-x's are easy to find, and less expensive, but not as good.   But the "good" expanding 300blk subs blow "good" expanding 9mm subs out of the water.

With that said, there MIGHT be a game changer on the market.  I'm hoping someone does a gel test soon, and when I post the weight pics, I'll post one I dug up...but it is the PSA/AAC 220gr Sabre Blade black tips.  
https://palmettostatearmory.com/aac-sabre-blade-black-tip-300-blackout-220-grain-20rd-box-ammunition.html
Yes, AAC makes an EXPANDING (or so they say), ballistic tipped 220gr sub that is less than a dollar per shot.

Admittingly, .300 blackout was only gun explosion I ever had. But it was reloaded .300 blackout IN 300 blackout. Still want to know if it was a pressure spike from an unresized pull down 150gr FMJ or a powder issue. Possibly from my cut down .mil 1x fired LC cases... still no clue on that.

It only popped the mags out, even the mags was fine.

Why would you use FMJ for a terminal ballistics comparison?

You're talking subsonic .300 Blackout, show us loads that are superior to good 9x19mm loads where it actually counts.  Let's see the gel tests, and the average expansion.

Agree - i don't see a .300blk doing anything better than 77gr TMK terminal ballistics-wise, aside from out of very short barrels. The only thing .300blk offers as an advantage is subs IMO. When people start talking about ballistic superiority of one sub round over another at any sort of distance...well, sure, it may be technically correct but it's a reach at best and a very poor choice.

300yds with a 10.5" 5.56? No sweat.

First off.

Glad you're OK. Seems like very few people are hurt when this happens and I'm grateful for that.

Caliber mismatches are no joke. I store ammo separate. I don't keep any loose stored ammo. I load my mags before the range and only load with 556 or 300 out of the ammo closet. I only use lancers with 300, and aluminum/steel for 556. I double, triple... quadruple check that I have the right mags.

I know what's in my mags the same way I know whether a chamber of one of my firearms is loaded. Complacency and firearms is a bad mix.

"I didn't know it was 300" is caused by the same issue that results in "I didn't know it was loaded"

Yeah that makes sense.  I guess my brain was just wrapped around the projectile that was twice as heavy.

Even without a weight difference there's still nothing I see a .300 doing so much better than any 556 that would want me to buy into it.

Just wanting something is a complete valid reason though so I get why some people have them.

Winchester 64gr JSP I have seen 10s of thousands go down range with zero problems over several years used/issued out.

First round fired.

No thread.

What do you think was the cause of the kaboom? (...and zero chance it was a stray reload)

Brand new BBl?   Cheap brand?  My first thought would be some sort of residue still in the barrel.  If malonited - the salts.  I've seen cheap brands not scrub those out.  conventional cleaning won't do it.  Has to be done with hot water.

Here are the weights.
110gr Hornady Black V-max from the 200 round ammo cans that used to be offered and 77gr IMI SMK.  
Side by side, they look different enough that it seems like KB's should not happen, but it clearly does.  Gotta be extra extra extra careful if running both.  I put mag bands on the mags AND the uppers, but that is really for other people since I don't shoot 5.56 anymore.  Clear Magpuls and Lancers might save some uppers in the future, at least during the daytime.








Bonus content!
Remington 220gr FBHP before and after (dug out)




PSA/AAC/Sabre 220gr Blade Black tips before and after (dug out).  Note: The Sabre round is boat tail.   I wonder what the BC on that thing is and how the expansion is when hitting a real target?

Glad you’re ok OP except the minor injury to your foot.

This is the main reason I’ve never added a .300 blackout upper to my collection, that and I don’t want to stock another caliber. I’ll stick to 5.56 7.62x39 and x51 as well as 9mm ARs.

Totally this.

Glad you weren't really hurt, OP.

My fear is not the 300BO gun blowing up but the possibility of the 300BO ammo somehow getting mixed in with my stuff

I actually took this picture of a guy to my left, at the range.



The guy had 2 identical looking supressed pistols/SBR's.

As the range-session progressed, he was dropping rounds.  And then running them.   Best part was "I thought there were 5 here, but only see 4...  oh there it is"    you can't make this up.

No kaboom - to my surprise.

Headspace as indicted above... ZERO, AS IN, NO FUCKING WAY A .223/5.56 RELOAD OR A .300 BLACKOUT [I DO NOT OWN A .300 BLACKOUT] FOUND IT'S WAY INTO A FACTORY BOX (the only reloads for the last 39 years have been commercial reloads in 9mm )... a new BCA barrel I looked through to be sure the hole went all the way through!!!!!!
I ran a patch through the barrel to make sure it was dry!!!

Yea we got that it wasn't an ammo issue in your specific example.  Nobody said different.  What I'm saying , and Julian Hatcher of Hatchers Notebook says, is that excessive headspace isn't going to cause a Kaboom of your gun.  It'll stretch and break a shell - maybe.  But you can even fire 308 in a 30-06; which is half an inch of excess headspace, and that doesn't kaboom a gun.  Happened all the time when they switched Garands to .308, and used an insert to convert old 30-06 guns.  the insert would eject out all the time and in went a .308 round.  No kaboom.

Where headspace can really get you is if you have too short headspace with an otherwise out of spec bolt/firing pin.  Now your bolt isn't locked, and OOB.  In a regular normal AR15, it'll just go click, because the bolt has to rotate for the carrier to go far enough for the pin to clear it's way to the primer.  I've done that many many MANY times.  No kaboom.  just click.  

Headspace didn't Kaboom your BCA.  Something else did.  

Top suspect on a brand new barrel is that it had a bore obstruction of some form, and of a nature that a dry patch wouldn't push out.  That could be a number of things.  Including just maloniting salts, which require a water-soak to remove.  Which they are supposed to do at the factory - and a cheap budget outfit maybe did fully and correct - or maybe didn't. I've gotten parts that were visibly blocked from not doing this correctly.  Just because you were able to push a dry patch through, doesn't mean that wasn't a .21" diameter bore due to maloniting salts, which will repeat the same effect this OP is about: 60,000 PSI pushing a bullet too big for the hole it's got.  Not saying that was for sure it, but saying that could be.  Or maybe something else, but it wasn't headspace alone that blew you up.  And apparently it wasn't your ammo.  And you're probably even right on that, since it would be a remarkable coincidence for bad ammo of the same type heavily used to date and you don't do .300 BO; so I agree, it would be far less likely for the kaboom on a brand new barrel install to be coincidental to the ammo, vs something amiss with the known low quality low cost barrel manufacturer on the very first shot fired.  Only other potential item might be the possibility that you have spare bolt cam pin laying around you can't recall where that ever came from - but I doubt it; I'm going with a defective barrel - and I doubt it was headspace.   Or maybe they screwed up the barrel extension, and it rotated with the bolt and only partially locked.  Who knows.

This happened to a guy at work while shooting with his son.  We were at work and asked me if I had ever heard of PSA uppers blowing up for no reason.  I asked him what happened and he said he took a shot and the upper came apart.  

As I started probing, what ammo, what caliber, bingo.  He said he was shooting 223/556 when he ran out, so his son asked him if he wanted some of his ammo and gave him a magazine.  Umm. what was your son shooting?  His 300 blackout.  Does he also have a 5.56 rifle?  No he only brought the 300 blackout that day.  Well duh.

Fortunately or unfortunately, the AR is a well designed and very safe design that has undoubtedly prevented untold Darwin awards.

Ohhh.  It sounded like you were afraid of the guys at your club shooting .300 Blackout next to you.

Simple solution.

1) Throw all your .300 Blackout in the trash.
2) Buy 7.62x39mm barrel, bolt, mags, & ammo.
3) Profit.

That sure sucks ass...

Just use dedicated .300 BLK mags, write on them, and keep the ammo separated.  

A .300 BLK Pmag will feed blunt nose projectiles like the Hornady Sub-X 190 gr better anyhow.  

Hand wringing over inter operability isn’t needed.  Some things in life are more dangerous than others.  It is good that you only need to swap a barrel, it saves a lot of money for shooters and manufacturers.  If the .300 BLK was not able to use standard 5.56 parts, it would not be popular to begin with anyhow.  It is fine as designed- a way to shoot .30 size bullets from a standard AR15 with minimal parts changing.

If you are worried about it, just shoot subs.  That is where .300 BLK stands out anyhow.  And pay attention while loading.  If truly worried about it, just don’t own one.  If you want to visually inspect all your 5.56 ammo, load it all onto stripper clips.  

If you are the kind of inattentive shooter who occasionally puts 9mm thru a .40, well then maybe it isn’t the caliber for you though.  (There are indeed plenty of people like this in the world, just go teach a class where the ammo is supplied, with a mix of 9/.40/.45 shooters, it will happen!  This is despite the fact that a flat nosed .40 looks nothing like a round nose 9mm…)

For all the worry about what can happen, when people truly fuck it up, it basically just breaks parts.  The rifle’s design contains the mishap for the most part.  If a .300 Blk kaboom in a 5.56 gun tended to kill people, it might be a different story.  Costing money is a constant in this life when you have a major fuck up….

If we wanted a perfectly safe hobby, we would not be messing with firearms anyhow.  Always the potential for something to go wrong.

Good on the OP for the safety reminder.  But some of the over the top concern is ridiculous…

Lot of truth there….

I know this is an unrelated issue, but I agree that the issue likely wasn’t the headspace…  hard to diagnose though without more actual info.

While I would love to see a better terminal performance than 190 SubX that was sub MOA capable, I run 190 SubX because it is sub MOA and the Lehigh is not. And while SubX is in fourth place in terminal performance behind the Lehigh, Maker, and HST 147... arguments about which subsonic expanding bullet has superior terminal performance is like arguing which midget is the best prize fighter... it's just not important because they all are horrible.

To me, the MOST important factor for terminal performance of subsonic is SHOT PLACEMENT. The SubX is the clear winner there. It is more accurate than Lehigh, twice as accurate as Maker, and three times as accurate as HST 147. Because of that, for anything past 25 yards, the SubX is the king IMO.

Now if factory AAC subs can expand better than SubX and print 5 round groups under an inch at 100 yards and expand fully out to 150+... you can call me converted.

Until then, precision trumps terminal performance for weak ass subs that are 147 9mm or above power, but not quite .45 ACP 230 +P power.

OP, I wanted to give you a huge thanks for being man enough to post what happened to you. I'm thankful you're okay.

I recently finished up a 300 BO and I'm very aware how easily I could have an incident like you experienced.

My solution is tan PMags for 300 bo only plus bright red bands.

This is one of those things that should be rare but it is rather uncommon at this point.  I have personally witnessed someone do this and watching a grown man nearly cry because the nearly 3K he spent on building his 5.56 down the drain.  All my 300blk mags are Lancer mags and labeled with the rubber bands.  I have done everything I think I can do to prevent this from ever happening as I keep my 300blk ammo separate from 5.56 and use a dedicated brand/unique magazine that is also labeled.

7.62x39mm says hi.

Everything reasonable

 
Keep in mind not everyone owned an AK or SKS before owning an AR.  
300blk is a barrel change away with an AR15.  Just getting into 7.62x39 will incur a much greater upfront cost, not to mention a new manual of arms and more spare parts/mags.   I won't get into the odd duck that is a 7.62x39 shoehorned into an AR15.

Plus ammo isn't all that much cheaper now (and not everyone stocked up on Russian steel case and 3 cents per metric ton back in 1983).

When you start getting into really short barrels, there really isn't a performance advantage over 300blk.

Clear and/or unique mags
Mag bands
Keep ammo separate
Make the guns visually different
PAY ATTENTION!

Even with that, poop still happens.  Live and learn.

 7.62x39 is a barrel change, bolt change, & mag change on an AR.  No different manual of arms, not a significantly higher upfront cost.  And it won't blow up your 5.56 guns.

If you grabbed a bunch of UniMags before they were discontinued, you don't even have to change mags.

I am told, however, that the bolt becomes a wear item and periodically sheds lugs.  

One of the guys I shoot with goes through bolts frequently.  He always keeps a spare and when he breaks a bolt he buy a new spare.

Shit happens. Glad you’re ok.

Can't say I personally recommend 7.62x39 in the AR platform.  It's been tried many times - with many problems.  Between the shape, the magwell, and the bolt-head size, it's just a tough one to get done right.  If I may - 6.5 Grendel has been much better refined and does well in the AR platform, and was specifically designed to be the most ass you can fit in an AR platform successfully.  There were some early teething issues (like always), but today, very rare to have any decent bolt break in 6.5 Grendel.

Yup, bands and plastic mags for 300BO, metal mags for 556. Yes, I still tap my mags against my headgear/head

Few months back I was out at the range and a guy had a 6.5G.  He was popping primers, cratering primers and all his cases looked like over pressure.  His brass kept landing near me and I finally flagged him just to show him his brass.  He did not seem to take it very seriously and continued shooting.  That was my first experience with some shooting 6.5G and someone who did not take the signs of over pressure very seriously.

If I were to do a barrel, bolt, and mag change on a small frame (to avoid KB's), it would be in one of the following:

300 Ham'r (7.62x41 that even uses the same bolt.)
350 Legend
6.8SPC
6.5G
6ARC

The only reason I would consider 7.62x39 in an AR now is if I were already sitting on a boatload of surplus ammo...and if I were already sitting on a boatload of ammo, chances are, I would also (most likely) already have a gun to shoot that ammo.  I personally would not go 7.62x39 just to avoid the possibility of KB's if I were not already invested in that caliber (especially shoehorning it into an AR).  Even more so with UniMags being discontinued.

One thing is for sure, the pricing dynamics have really changed if you don't reload.  FMJ .223/5.56 is a penny or two cheaper than FMJ 7.62x39, and that is only about about 8-10 cents cheaper than 300blk FMJ.  

I do wonder if 6.5G will become cheaper based on what PSA/AAC does?

I bring up 7.62x39mm in .300 threads b/c they have very similar exterior ballistics.  One has more powder capacity but lower pressure, but the end result is very similar.  And there are now subsonic 7.62x39mm loads, I'm told.

Hornady offers them. I'm sure there are others as well.

Glad to hear OP is okay. I only shoot M193 factory loads out of my rifle. I'm not entirely sure if that'll totally protect a Kaboom but I guess only time will tell.

I don't think ballistics are the top reason why people get into 300blk.  If I specifically wanted 7.62x39 ballistics, I would have gotten into 7.62x39 (or 6.5spc or 6.5G).  I think people get into 300blk because (in no particular order):
*It is just a barrel change away on the AR platform, and it actually works.
*It short/super short barrel characteristics (plus it works just fine from a 16").
*Ability to shoot supers and subs, both suppressed and unsuppressed without any adjustments (once tuned).
*Ability to reload using extremely common .308 boolits and .223/5.56 brass.


300blk is a caliber that IMO does not compete with most other calibers, I think that it competes with specific weapons/platforms instead because it plays mostly in a specific space.
To me, it does not compete with 9mm or 5.56 or 7.62x39, it competes with MP5's, Mk18's and Draco's.  So when 7.62x39 is offered up, the use-case does not really apply.  Even more so with Russian imports on hold now (if you don't already own something chambered in 7.62x39).

---------
OP, do you know what type of rounds slipped in your 5.56 stash?

I ask because I wonder if it is FMJ rounds that slip into 5.56 stashes?  I understand it was at night, but just thinking about that round getting in there in the first place.

I just realized that a most of my 300blk rounds are so visually different from my 5.56 that it would be very difficult to not notice one in the light.
A vast majority of my rounds are 110gr Vmax, Tac-tx, or Varmageddon, which all have black or red ballistic tips.  If not, then they are either Aussie Outback (from the GO BOGO) 144gr FMJ with BLACK brass cases or the 145gr Wolf FMJ in the grey steel cases.   It probably helped that Hornady Black V-max used to be sold in 200 round ammo cans for not much more than FMJ, so I purchased that to shoot rather than FMJ.  I don't own any 5.56 ammo with ballistic tips, or black or grey cases, so that helps from a visual standpoint.  I do have some brass/brass 300blk ammo that could look like my 5.56 rounds, but these threads remind me to be extra careful (even though I don't shoot 5.56 anyway).