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Posted: 2/15/2018 8:27:51 PM EDT
[#1]
I've read it somewhere, can't remember where, about the same thing for 6.5 Grendel. Probably saw it here or on the 6.5 Grendel forum. I recently put together a 12" 6.5 Gr pistol, I've only put a few rounds thru it for a function check, I don't think the muzzle blast is any worse thatn my 10" 5.56 pistol.
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Posted: 2/15/2018 8:34:34 PM EDT
[#2]
when loaded with what powder ?
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Posted: 2/16/2018 8:12:01 PM EDT
[#3]
factory supersonic loads.
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Posted: 2/16/2018 8:59:43 PM EDT
[#4]
Quote HistoryQuoted:
factory supersonic loads. Quote HistoryQuoted:
factory supersonic loads. If you didn't convert the powder well before the gas port, you would see kernels inside your BCG until they clogged the gas tube, resulting in the rifle no longer working and having your gas tube rupture. Think about the chamber pressure, heat, and solid kernels flashing over due to the nitrogen content and chemical composition that lends itself to becoming a gas when a spark lights it off inside a contained vessel. There is no space for the powder to go when contained inside the high pressure gasket known as your brass or steel case. It's an instantaneous furnace that goes from zero to over 50,000psi where it sits. The resulting resonant pressure wave from the detonation propels the bullet through the bore until it exits. The muzzle flash you see is not powder being burnt. It's the gas wave escaping behind the bullet into ambient atmosphere, which is more nitrogen and oxygen to fuel the combustion. The carbon residue you find in the action is simply that, carbon residue from the graphite in the propellant. Bill Alexander: Graphite is added to the manufacturing process to prevent static build up. Correctly formulated propellents which have been manufactured for use in a semi automatic rifle will be more heavily graphited to provide some level of lubrication in the gas residue. Most new military powders will have the graphite level specified within the overall performance specifications. Graphite is graphite unless you reach the sublimation temperature, 2400 C it will deposit into whatever mechanism it is blown onto and it will provide a level of dry lubrication. Graphite in powder is a very careful balancing act. The burn characteristics of the powder and the other chemicals used to retard the burn rate and remove the residual water from manufacturing must produce a very fine soft residue rather than heavy baked contamination. The newer generation of propellents are well engineered in this respect. The graphite rarely takes the form of dust within the powder but rather is diffused into the surface of the powder grains. One of the things we are seeing is that the powders are actually becoming more and more specialized. If you shift case volume or operating pressures everything changes and what was a perfect powder can become a disaster. Bill Alexander |
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Posted: 2/16/2018 9:03:32 PM EDT
[#5]
Complete powder burn is not an argument to compare one with the other.
What these internal ballistics comparisons in short barrels come down to is: Fast burning powders in one versus more efficient cartridge/chamber design in the other chasing muzzle velocity for the people who still live in the 20th century's approach to measuring a cartridge's performance. |
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Posted: 2/17/2018 1:06:53 AM EDT
[#6]
Ad mentioned above, unburnt powder exits the muzzle as little sparks, and requires barrel lengths far shorter than most anyone realizes.
What few people seem to understand, also, is that the bullet is still doing a lot of acceleratibg long after actual deflagration occurs. In any case, you will probably hear a few anecdotal answers, but none of them will actually tell you when the bullet has stopped acceleratibg, which for most rifle cartridges is up in the 30"+ range. |
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Posted: 2/17/2018 7:30:47 AM EDT
[#7]
Quote HistoryQuoted:
Ad mentioned above, unburnt powder exits the muzzle as little sparks, and requires barrel lengths far shorter than most anyone realizes. What few people seem to understand, also, is that the bullet is still doing a lot of acceleratibg long after actual deflagration occurs. In any case, you will probably hear a few anecdotal answers, but none of them will actually tell you when the bullet has stopped acceleratibg, which for most rifle cartridges is up in the 30"+ range. Also, not sure there's any reason to think that the muzzle flash is ionized gas (i.e. plasma), it's just good old combustion. -Stooxie |
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Posted: 2/17/2018 8:47:42 AM EDT
[#8]
Combustion of what? It would seem really inefficient to pack the powder with such an imbalanced chemistry that sufficient fuel remains after "complete" deflagration (;)) to actually react with ambient oxygen and combust.
I did some very rough math with the ideal gas law using 3300*F as the peak temperature and estimating the actual molecular mass and volume of the chamber and barrel. By my numbers, in all but the longest of barrels, the actual gas temperature remains plenty high enough to keep the gases in the plasma state, meaning they are hot enough to glow on exit. This further validates long-standing research into flash hiders which seek to diffuse and cool the gases as quickly as possible to minimize the larger observed "flash" of the gases all exiting as a single mass. So, lomg story short: 1) All the powder is burned in the first few inches, or pistol-length gas systems would end up with unburned kernels all in the action. 2) At practical barrel lengths, there is still enough pressure (and heat) in the gases to both continue accelerating the bullet, and to produce a visible muzzle flash. |
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Posted: 2/17/2018 9:43:48 AM EDT
[#9]
How long you been shooting?
-Stooxie |
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Posted: 2/17/2018 9:48:57 AM EDT
[#10]
These answers are very informative, but I think OP is trying to ask at what length is the bullet no longer accelerating. I don’t know, but I’d think it’d be a good bit longer than most any commercially available barrel. I’d wager it’s significantly farther than 12.5 in every loading imaginable to include heavy pistol calibers.
The real question is: How much velocity do you need to effectively kill/hit shit at the ranges you’ll likely be encountering? That may very well leave you with only needing about 12.5” give or take. I know it did for me. |
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Posted: 2/17/2018 1:45:32 PM EDT
[#11]
Also,
https://www.thehighroad.org/index.php?threads/22-barrel-vs-24-barrel.570474/ https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.68spc.com/68velocity&ved=2ahUKEwjb6O6ysJnZAhXGKWMKHbZICwAQFjAAegQIDRAB&usg=AOvVaw2gTK8fK44Hhf6XOu00Wx40 On the quickload PDF, velocity per inch is dropping by a couple fps every inch as it approaches 24" (in the low-20s). Conservatively extrapolating 3fps^2 per inch gives us roughly 31" before the bullet actually stops accelerating. Quote HistoryQuoted:
How long you been shooting? -Stooxie |
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Posted: 2/17/2018 2:52:08 PM EDT
[#12]
Quote HistoryQuoted:
Ad mentioned above, unburnt powder exits the muzzle as little sparks, and requires barrel lengths far shorter than most anyone realizes. What few people seem to understand, also, is that the bullet is still doing a lot of acceleratibg long after actual deflagration occurs. In any case, you will probably hear a few anecdotal answers, but none of them will actually tell you when the bullet has stopped acceleratibg, which for most rifle cartridges is up in the 30"+ range. 
 Addressing the OP's question, it really doesn't matter since he's asking about how much barrel is needed to "fully burn" the powder. If leakage is the cause of a small amount of burning propellant to slip by, the barrel length will only determine how much of an effect it has once it clears the muzzle. For me, a 12.5" or shorter AR15 barrel is best when suppressed or tamed with some type of muzzle device anyway. |
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Posted: 2/17/2018 4:15:30 PM EDT
[#13]
Quote HistoryQuoted:
Out of curiosity, are you implying that somehow the XX number of years you are about to throw out will inherently qualify you to speak to any number of exceedingly advanced theoretical firearms topics? I.e. plasma, ionized gas, which generally requires enormous amounts electricity, magnetic fields and a vacuum. None of which are present in the systems we are talking about. There's no plasma here. And to say that "all powder is burned in X amount of length, thus a barrel of X or greater length shouldn't produce a flash" isn't true for all kinds of reasons. Otherwise un-reacted gasses, that have consumed whatever oxygen is in the barrel, will flash once exposed to the air. -Stooxie |
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Posted: 2/17/2018 4:49:50 PM EDT
[#14]
Quote HistoryQuoted:
Combustion of what? It would seem really inefficient to pack the powder with such an imbalanced chemistry that sufficient fuel remains after "complete" deflagration (;)) to actually react with ambient oxygen and combust. The powder never burns completely, and of course a longer barrel won't help that. It will help with things like muzzle velocity, muzzle flash and noise level. You can make a cartridge, especially one with a low operating pressure like 30/30, run real rich with lots of left over actual powder kernels. Just mismatch the powder. Use a powder too slow/better suited for a higher operating pressure. And again the barrel length still won't help any. Where are you guys getting plasma from?? http://www.navweaps.com/index_tech/tech-090.php |
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Posted: 2/17/2018 5:00:10 PM EDT
[#15]
While the glow we see in a flame is indeed ionized gas, perhaps we can ignore that for more traditional definitions of plasma. That is, visible flames may contain "some" plasma, but are not fully plasma on the whole.
In any case, I can see how you might be right about powders deliberately running "rich," leaving unconsumed reactants left to potentially react with ambient air. Still, it sounds like we do agree that the powder charge completes its reaction within several inches, and actual bullet acceleration is still occurring long after any production barrel length. Good discussion! Thanks :) . |
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Posted: 2/17/2018 5:35:09 PM EDT
[#16]
You're welcome.
As for "plasma"... it ain't plasma... 
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