300 blackout–same lower/upper/bolt as 5.56?

[Boolseye]

Is the barrel the only difference in 300 Blackout?

[John Allen]

As far as I know that is it. I bought a 300 upper and put it right on my lower. It runs magpul mags with no problem.

[Finster101]

Yep, all the same except the barrel. Mags too.

[Dystaxia]

Is the barrel the only difference in 300 Blackout?

Confirmed - That is correct.

[nicholst55]

Don't forget the thingie on the end of the barrel! Hard to get a .30 bullet/boolit through a .22 hole!

I jest; different threads on the .224 and .308 barrels.

[kbstenberg]

Would it be the same for any of the 223 based cartrigas? I like the 7mm TCU. Kevin

[GARD72977]

You will find that the OAL of the 7mm TCU is a bit much for the magazines.

[Artful]

you can find many wildcats for AR15 based on 223 case head size
6.5mm whisper, 7mm whisper, 300 whisper, & 338 whisper #2 based on 221 fireball cases
6x45
7.62x40 Kurt
338 Thumper ( http://www.bwefirearms.com/338.html )
there's 17's, 20's, 25's it's just what will fit in the magazine and feed into the chamber.

[Crytes]

also if building an upper the gas system tends to be shorter than what you'd use for 5.56mm

[Jupiter7]

also if building an upper the gas system tends to be shorter than what you'd use for 5.56mm

Not really. 300blackout was developed to run in a m4 with carbine gas system, buffer and spring. Lots of people build pistol length gas systems, but not necessary for a properly gassed gun. I have both, they are equally reliable.

[thehouseproduct]

Not really. 300blackout was developed to run in a m4 with carbine gas system, buffer and spring. Lots of people build pistol length gas systems, but not necessary for a properly gassed gun. I have both, they are equally reliable.

I have to disagree. It all depends greatly on barrel length, desired bullets and speeds and noise levels. I have a 13.5" barrel with a carbine length gas system that barely runs anything because of the decreased dwell time compared to 16" barrels. If I was doing it again, I'd pick a pistol length system with an adjustable gas block on top of a 0.120" port for maximum versatility. Many reloaders want to run the fastest powder possible to make it as quiet as possible.

[500MAG]

Wow, the last time I asked a question about an AR15 under the military rifle section, the old timers jumped all over me.

[bikerbeans]

Wow, the last time I asked a question about an AR15 under the military rifle section, the old timers jumped all over me.

500,

I'm not an old timer but I will jump all over you if you want.;-) Since an AR15 isn't a military rifle but a derivative of a military rifle, I can see how maybe the discussion doesn't belong here. A friend of mine who collects military firearms thinks that any gun built after the end of the Third Reich doesn't qualify as a real military gun.


BB

[Jupiter7]

I have to disagree. It all depends greatly on barrel length, desired bullets and speeds and noise levels. I have a 13.5" barrel with a carbine length gas system that barely runs anything because of the decreased dwell time c
ompared to 16" barrels. If I was doing it again, I'd pick a pistol length system with an adjustable gas block on top of a 0.120" port for maximum versatility. Many reloaders want to run the fastest powder possible to make it as quiet as possible.

Agreed, in short barrels, pistol length is the way to go. I was indirectly referring to 16" + barrel lengths. Both my 8" and 10" are pistol length. 16" is carbine.

[Liberty'sSon]

Agreed, in short barrels, pistol length is the way to go. I was indirectly referring to 16" + barrel lengths. Both my 8" and 10" are pistol length. 16" is carbine.

I'm starting to think that the consensus, or better yet, the simplest thing to do is us a pistol length gas system on all 300 BO barrels. I haven't heard of pistol length causing any problems. Have any of you folks? I got my 16 in working with carbine length ( after I opened the port) but any future builds will be pistol gas systems .

[thehouseproduct]

I'm starting to think that the consensus, or better yet, the simplest thing to do is us a pistol length gas system on all 300 BO barrels. I haven't heard of pistol length causing any problems. Have any of you folks? I got my 16 in working with carbine length ( after I opened the port) but any future builds will be pistol gas systems .
I'd think that the worst would be that you'd be over gassed for super sonic loads. For the level of reloader that most people on this forum are, an adjustable gas block solves this problem easily. I want to find a way to run my cast book it's subsonic. Up till now, the carbine system on my gun needs so much gas that even with 250gr boolits, the cast lead doesn't generate enough pressure until it's super sonic.

[Moonie]

I'd think that the worst would be that you'd be over gassed for super sonic loads. For the level of reloader that most people on this forum are, an adjustable gas block solves this problem easily. I want to find a way to run my cast book it's subsonic. Up till now, the carbine system on my gun needs so much gas that even with 250gr boolits, the cast lead doesn't generate enough pressure until it's super sonic.

What loads have you tried, I hear AA1680 works well for subs with boolits over 200gr and I have recently had good luck with RL-7 and 235gr and cycling with a carbine length gas.

I first tried H4895 and it worked very well for subs with my 245gr boolit, but the SD was high.

[felix]

Where would the 7mmTCU be too much? Case body? ... felix

[GabbyM]

My first SIL is all up in getting a 300. Then he does live in a state where suppressors are legal. Other than a suppressed gun. 25x223 or my favorite 6x45mm is more of a rifle trajectory. Whatever you do don't buy into the BS of a 300 black out being a 30-30 or even a 7.62x39. Because it isn't . Not anywhere in the class of a 30-30. 300 Blackout is what it is. Can stand on it's own merits without the lies.

I'm fairly invested in 6mm with boolit molds neck turning tools and such. So would gravitate into a 6x45mm but other wise a 25x223 would be high on my list. Run a 20 inch barrel with suppressor with 120 grain cast boolits and your muzzle blast will be low. Not the puffy puff 300 Blackout will yield but for hunting outside of town it'll do even with super sonic ammo.
I shoot my 243 AI with 26 inch barrel using a cast boolit over 11.0 grains of Unique powder. It simply cracks like a 22 WMR. 84 grain boolit going 1950 fps.

Instead of using some pistol length barrel use a rifle length then have the can come back to the forearm. Over the barrel.
By rifle length I mean 20 to 26 inches not 16". I shake my head at what some consider rifle length VS pistol length. Since in my little cut off world a 16" barrel is a pistol not a rifle. It's all Symantec's but in the end the gun needs to work.

[Jupiter7]

My first SIL is all up in getting a 300. Then he does live in a state where suppressors are legal. Other than a suppressed gun. 25x223 or my favorite 6x45mm is more of a rifle trajectory. Whatever you do don't buy into the BS of a 300 black out being a 30-30 or even a 7.62x39. Because it isn't . Not anywhere in the class of a 30-30. 300 Blackout is what it is. Can stand on it's own merits without the lies.

I'm fairly invested in 6mm with boolit molds neck turning tools and such. So would gravitate into a 6x45mm but other wise a 25x223 would be high on my list. Run a 20 inch barrel with suppressor with 120 grain cast boolits and your muzzle blast will be low. Not the puffy puff 300
Blackout will yield but for hunting outside of town it'll do even with super sonic ammo.
I shoot my 243 AI with 26 inch barrel using a cast boolit over 11.0 grains of Unique powder. It simply cracks like a 22 WMR. 84 grain boolit going 1950 fps.

Instead of using some pistol length barrel use a rifle length then have the can come back to the forearm. Over the barrel.


By rifle length I mean 20 to 26 inches not 16". I shake my head at what some consider rifle length VS pistol length. Since in my little cut off world a 16" barrel is a pistol not a rifle. It's all Symantec's but in the end the gun needs to work.

In the AR world. 20" is rifle, 16" Carbine. The appeal for short barrels in 300blk is the very little velocity lost from 16" down to 10" barrels. And, I can shoot 160gr boolits at 1950fps in my 16"'carbine. Most the "true" rifle wildcats from .223 are very limited by mag length. 6x45 would be my second choice and then the 25/223. But they would benefit from a bump in OAL allowed in single shot or bolt action rifles. But for hunting out to 200yds , hard to argue with a 30 cal heavy boolit.

[Artful]

Where would the 7mmTCU be too much? Case body? ... felix

Overall loaded cartridge length is too long to work thru AR-15 magazine which was designed to work
with Overall length of 57.40 mm (2.260 in), using the same case with longer 7mm bullets would exceed that length.

Example would be 130 grain 7mm bullet - that's 2.500
my 154 SP was loaded to 2.700 - you can see the problem...

the Ugalde chambers were spec'd for T/C Contender barrels usually with long throats.

[felix]

Thanks, Art! I can dig that. My idea for a 7 or 270 would be circa 100 grainers in the AR, which should work without too much of a body chop? Thinking of a 12 twist barrel for both sonic and subsonic. ... felix

[Artful]

Felix the 6.8 SPC is a 270 based on a case larger in diameter than 5.56 but would be a good starting point for a wildcat based around 7mm or 270 for use in AR15 platforms
http://en.wikipedia.org/wiki/6.8_SPC
http://upload.wikimedia.org/wikipedia/commons/thumb/6/66/6.8SPC.jpg/220px-6.8SPC.jpg
6.8 SPC vs 5.56 comparison
You could try using 7.62 x 40WT brass necked down
http://www.wilsoncombat.com/images/762x40/762x40-comparison.jpg
http://wilsoncombat.com/new/762x40-project.asp
as you aren't planning to the long heavy 175's and such

[thehouseproduct]

My first SIL is all up in getting a 300. Then he does live in a state where suppressors are legal. Other than a suppressed gun. 25x223 or my favorite 6x45mm is more of a rifle trajectory. Whatever you do don't buy into the BS of a 300 black out being a 30-30 or even a 7.62x39. Because it isn't . Not anywhere in the class of a 30-30. 300 Blackout is what it is. Can stand on it's own merits without the lies.

I'm fairly invested in 6mm with boolit molds neck turning tools and such. So would gravitate into a 6x45mm but other wise a 25x223 would be high on my list. Run a 20 inch barrel with suppressor with 120 grain cast boolits and your muzzle blast will be low. Not the puffy puff 300 Blackout will yield but for hunting outside of town it'll do even with super sonic ammo.
I shoot my 243 AI with 26 inch barrel using a cast boolit over 11.0 grains of Unique powder. It simply cracks like a 22 WMR. 84 grain boolit going 1950 fps.

Instead of using some pistol length barrel use a rifle length then have the can come back to the forearm. Over the barrel.
By rifle length I mean 20 to 26 inches not 16". I shake my head at what some consider rifle length VS pistol length. Since in my little cut off world a 16" barrel is a pistol not a rifle. It's all Symantec's but in the end the gun needs to work.
When people here are talking rifle, carbine or pistol length, we are talking about the length of the gas tube from the gas block to the upper receiver. It is not necessarily tied to the length of the barrel at all.

[thehouseproduct]

What loads have you tried, I hear AA1680 works well for subs with boolits over 200gr and I have recently had good luck with RL-7 and 235gr and cycling with a carbine length gas.

I first tried H4895 and it worked very well for subs with my 245gr boolit, but the SD was high.
I've tried even slower than 1680, the 13.5" barrel length is what is killing me.

[felix]

Art, I really like the 6.8 SPC as it stands! It really does not need improvement to make a circa 100 grainer do 2400 fps. However, I do not wish to get another full custom upper or for that matter a matching lower. Only a custom barrelled bolt gun will do, but that is just greed on my part. So, I will just dream of shooting one until a custom action comes along already configured. Won't happen because the PPC standard bolt is too close in specs. ... felix

[Artful]

Felix, you just need to keep a lookout on the used rifle market
Ruger made a 6.8 SPC Hawkeye
http://www.realguns.com/articles/333.htm
Remington made a model 7 and 700
http://www.remington.com/en/products/archived/centerfire/bolt-action/model-seven.aspx
I would think if you didn't like those - look at savage as they make interchangeable bolt heads
and barreled rifles.

[Boolseye]

Folks,
as OP, may I diverge a bit here: what's the feeling on building a new upper but not worrying about a separate BCG? identical uppers.
-BE

[thehouseproduct]

Folks,
as OP, may I diverge a bit here: what's the feeling on building a new upper but not worrying about a separate BCG? identical uppers.
-BE
I've HEARD that sharing BCG accelerates wear on the BCG as it constantly tries to wear to match the barrel extension it's going into. That's internet hearsay and In reality I couldn't imagine it making a difference unless you're shooting thousands and thousands of rounds from each.

[Boolseye]

THank you for that,
-BE

[felix]

Will do, Art! ... felix

[Artful]

Folks,
as OP, may I diverge a bit here: what's the feeling on building a new upper but not worrying about a separate BCG? identical uppers.
-BE

Bolt carrier no problem - but I would get a separate dedicated bolt head for each upper.
The wear pattern is unique to each upper, and like swapping chains on motorcycles you
will accelerate wear on either the bolt head or the barrel extension.

[Boolseye]

Artful,
Thanks for your considered reply.As a bicyclist and motorcycle rider I know just what you mean.
I think that, since I will be switching back and forth, I will need a new BCG for the new 300 AAC upper.

That said: is it a simple matter to switch out bolt heads?
-BE

[Artful]

http://www.youtube.com/watch?v=r3uOZVl8_EY

[bikerbeans]

220g subsonic J-words with 11.5g of H4198 cycles perfectly in both my carbine 300 BO and my son's 9" SBR 300 BO. Going to try the Lee 300 AAC boolit next with the H4198.

BB

[Boolseye]

Nice. Thanks again Artful.