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barrel length and powder burn
nemesisenforcer
Member Posts: 10,513 ✭✭✭
we all know that longer barrels burn more powder, but in what way to do shorter barrels burn powder? In other words, if I load a case with 50 grains of powder that is substantially all burnt in a long barrel but only 40 grains (80%) is burned in a short barrel, if I up the charge to 55 grains, will only the 40 grains be used or will it be 44 grains (80%?)
Does more powder in a case equal more powder burned in the shorter barrel (but still less than in an optimal length barrel) or are you wasting that much more fuel and reach a point of diminishing returns on an absolute level?
Does more powder in a case equal more powder burned in the shorter barrel (but still less than in an optimal length barrel) or are you wasting that much more fuel and reach a point of diminishing returns on an absolute level?
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The truth is that the pressure peak marks the effective end of powder burn, and the pressure peak can occur even before the bullet leaves the case in some rounds, and within eight or nine inches of bullet travel in seriously over-bore magnum rifle rounds.
Understand that "effective end of powder burn" does not mean that every bit of powder has burned. But it does mean that almost all the powder that will burn already has. A few kernels will continue to burn after pressure peak, some others will actually go out, and others never ignite at all. But after the pressure peak, you have gotten all you are going to get from that powder charge.
You get higher velocity from a longer barrel because the high-pressure gas has longer time to push on the bullet. That's it plain and simple. There are one or two optimum powders for a given set of cartridge components. That powder(s) will give the best performance regardless of barrel length. Any other powder will give lower velocity, again regardless of barrel length.
we all know that longer barrels burn more powder, but in what way to do shorter barrels burn powder? In other words, if I load a case with 50 grains of powder that is substantially all burnt in a long barrel but only 40 grains (80%) is burned in a short barrel, if I up the charge to 55 grains, will only the 40 grains be used or will it be 44 grains (80%?)
Does more powder in a case equal more powder burned in the shorter barrel (but still less than in an optimal length barrel) or are you wasting that much more fuel and reach a point of diminishing returns on an absolute level?
It has more to do with powder speed. The longer barrel allows a slower burning powder more time to fully utilize the gases pushing the bullet out. The faster powder builds peak pressure faster and is therefore better suited to the shorter barrel where excess gasses won't be wasted. So, it's not so much of how much gets burned, it's more a matter of how much gets utilized.
Understand that bullet and barrel diameter, bullet fit, barrel smoothness, case geometry, and load density all affect burn rate.
And FWIW, powder is not done burning at peak pressure. Peak pressure is simply the pressure reached sometime between complete ignition and consumption. Powder is still being consumed as it moves down the barrel. Unless of course we are talking about revolvers. Excess gases and unburned powder plasma vents off out the front side of the cylinder. Gases and plasma don't continue to push the bullet in the barrel. It gets what it gets when the trigger is pulled.
We've been down this "Rocky Road" before. As I stated in the past, if the powder was completely consumed then it wouldn't be burning out the end of the barrel. Try that at night again like I said before. Try some slow powder out of a short barrel and see what happens at night (when you can see a clear difference. Versus using a faster powder and not seeing the "big (I mean huge) flash" at night.
I know you hate to have proof thrown in your face Rocky but that's how it is. If you'll note the first part of what I said is NOT a different way of saying what you said. You simplisticly stated that the bullet goes faster because the gases have more time to push on the bullet. HINT: that only works if there is still gases EXPANDING to push on the bullet. If gases aren't EXPANDING then they aren't PUSHING. Understand too, that even though gases may not be pushing the bullet has reached an initial velocity that will still send it on it's merry way from the barrel at a decent speed. So a fast powder will still push a bullet out fast, just not as fast as bullet pushed by slower powder. Which could still be pushing the bullet to the end of the barrel.
As for the revolver, Once the port is vented, unless there is a point of impingement(something for the pressure to push off of such as a wall), there is no pressure pushing the bullet. In fact you, yourself stated some cartridges reach max pressure before the bullet ever leaves the cartridge. In that case I did say what you said but in a different way.
I don't like turning this into a personal fight, but I'm telling you this is just like me (the mechanic) tell you (the pilot) how things really work. And, you saying no, it works like "blah, blah blah, (just like I told you but 'different').
I swear this reminds me of two pilot jokes I'll never forget.
Q: How many pilots does it take to change a light bulb?
A: One, he holds the bulb in place and the whole world revolves around him.
This is you to a "T". You state something and then stand there and argue until you've got it that you said the right answer.
I will tell you that when I came on this forum I thought I knew a lot. I didn't. At least as well as dispensing some (what I feel is) good information here I think I've learned a LOT here as well.
The second is:
Q: How do you know your conversation is EXACTLY half-way over with a pilot?
A: He says, "Enough about me, lets talk about airplanes."
Dude, I'm telling you again. Your hardline approach to "that's how it is" is what gripes me. Maybe it's my dislike for gunwriters in general (for which I have apologized to you in the past for generalizing). The "This is how it is and the rest of you don't know" mentality seems like trying to keep a 'one leg up on the public' campaign. You know, because you're a gunwriter and you're privy to all we can't see. Not so. It's just like bean-counters. You have to count them all to make the numbers matter. So, if you poo-poo me like you did the last time and say the "big flash" is just some unburned powder that never would have burned anyway, I'm going to disagree with you.
Here on this forum many of us work to see just how close we can get to the perfect load, and then find WHY. Most of us want to see if the next powder up on the scale of either pressure or speed or slower speed is going to give more velocity and the same accuracy. Yes, it is possible to have two different velocities give the same accuracy for the same reasons.
-Rant over
I'm really not qualified to argue thermodynamics so I'll just go with some basic redneck pondering. So correct me if I'm wrong.
Basically powder in any form is stored energy. As it burns it releases energy in the form of expanding gas. It seems the pressure would reach its peak as the bullet finds its sweet spot in acceleration (this would be altered by different burn rates) pressure builds as a stationary object becomes a mobile object. Efficiency increases because its easier to make a moving object to go faster than to make a stationary object go faster. It would seem that powder that continues to burn after peak pressure would continue to add acceleration simply by continuing to release energy by creating more expanding gas. If no more energy was added then the bullet would outrun the expanding gas and cause a vacuum and actually slow the bullet down by the friction of the barrel. Of course the barrel would have to be stupid long to prove this but ...
Am I on the right track??
Sandwarrior, as I've shown and proved, the powder gasses do not continue burning out the muzzle. I've shown that the flash is due to unconsumed gasses mixing with air and re-igniting. See the section on "Flashless Powder" in this link: http://en.wikipedia.org/wiki/Smokeless_powder
With all due respect to the intensity of your beliefs on this issue, your sources are in error. I didn't dream this stuff up; I'm merely relaying what real ballisticians and pyrotechnic experts tell me, in my best attempt at non-engineering terms. Half of what they say is over my head, so some of what I relay here may be technically off a bit. But the essence is true.
Powder burn is controlled by a number of factors- powder speed and charge weight, primer type and hotness, case shape and powder position, throat and bore dimensions, etc. However, all of these things boil down to one factor- all but the fastest powders need some pressure to burn efficiently. Try loading a 30-06 with 40 gr of 4831. You get a lot of unburnt powder, because the pressure developed by the load in quesiton isn't enough to cause consistent or total ignition. That powder has a burn temperature that demands a certain pressure and temperature to ignite completely that is not being met. Now try the same experiment with 58gr of the same powder- very clean load, very little unburnt powder. Why? Because the amount of fuel available reached a critical mass of sorts- enough was available to completely ignite the charge.
This applies to black powder as well. The more you compress it (greater pressure) the more complete and cleaner burn you get.
WHATEVER your charge, peak pressure does indeed develop either in the chamber or very soon thereafter in the barrel. The question is, is that pressure sufficient to consume the whole powder charge or not?
The short barrel/long barrel question enters into it secondarily. True, pressure peaks long before the bullet reaches the end of the barrel, but that doesn't mean that zero powder burn is happening at that point; also, a longer barrel allows the gas column to expand over a longer distance meaning it has a lower per cubic inch energy density by the time the bullet leaves... all leading to a fireball with a short barrel and just a faint puff in a long barrel.
This barrel length consideration IS, however, related to powder burn rate. A case full of slow powder, even if consumed completely, will create more gas and more flame than a small charge of a fast powder- and because the longer barrel distributes the same amount of energy generated by the burn over a larger area- you get less flame.
There is also a relation between barrel length and velocity (obviously). A longer barrel does indeed alow more complete burn of powder and transferance into plasma, so you DO get more velocity- even if pressure peaked a long time earlier.
Here's an interesting experiment for those who handload and have a chronograph. Take 2 guns chambered in the same cartridge, with different barrel lengths, and load each with a slow powder. Same charge. The longer barreled one produces a higher velocity.
Now take the same guns and cartridge, but load it up with a plinker load. Say a 30-06 with a charge of 5 gr of Bullseye (common reduced load for cast bullets). Do the same experiment.... the results? I've found that in most cases, the SHORT barreled gun produces a HIGHER velocity because of the very small amount of burning powder/plasma... just food for htought.
All of this is (or may be) interesting, but it has little import on the average reloader. The ballistic labs test powders most suitable for a given bullet/cartridge combo. Stick to that published data and you'll be fine.
Lets say we have a 20* shoulder angle in a cartridge, and the same cartridge with a 40* shoulder angle. The cartridge with the 40* shoulder angle, will not allow the plasma to flow out the case mouth as easily as it will from the same case as the one with the 20* shoulder angle. You can think of a hose nozzle. The pressure will build more quickly in the case with the 40* shoulder than it will in the same case with the 20* shoulder angle due to the fact that the sharper shoulder angle will cause the fraction of a millisecond more time for the plasma to exit the case mouth (same bore dia is a given). Thus, the same load of the same powder, will produce a faster pressure curve, but not necessarily a higher peak pressure, although it can/will happen.
An identical case, with .003" of neck tension, will show a different pressure curve than a case with the exact same load of powder and bullet, than one with say .007" neck tension. The amount of tension holding the bullet in the case neck, varying from one to the other, will cause changes in that curve, since it will take more pressure behind that bullet to "get it moving" from the case neck. A higher neck tension, will cause a faster build in pressure to peak pressure (although immeasurable by a human being, but by a highly specific piece of equipment). This is the reason the manufacturers of competition dies, make bushing dies for accuracy work. even .001" neck tension can make a big difference in accuracy as well as (ES) extreme spread and (SD) standard deviation of the load when shooting for groups. The barrel itself, will decide which load density, and which neck tension it likes best, there is NO HUMAN INPUT that changes that.
Now, lets say we have a load density we have found to be the preferred load for that particular barrel (given land and groove dimensions, smoothness, land corner angle, etc). The longer the barrel, the more time expanding gasses push on the base of the chosen bullet. Therefore, the longer the barrel, the faster the bullet leaves the muzzle, to a point. After a certain amount of length of barrel traveled, the gasses have less and less pressure, since the expansion area is increased with every .001" of barrel that the bullet travels. As the bullet moves foreward, the space from the case is increased, but the amount of propellant is a given. therefore, the more the bullet travels, the more the peak pressure is decreasing.
a longer barrel, will benefit from slower powders, since they take longer to burn, and will continue to push that bullet over a longer barrel distance. however, our current powders are highly efficient and burn efficiently in todays barrels.
unburned powder exiting a barrel, no matter how short, is just a wives tale. Studies have shown that all powder is burned during the first few inches in front of the chamber. The "flash" at the muzzle is simply an effect of how much gas is still pushing the bullet. The more gas pushing the bullet at the muzzle, the brighter the muzzle flash. Expanding gasses hitting new oxegen will flame up quickly, so the more gas, the bigger the flash.
Two points to consider: slower powders produce higher velocity partly due to the simple fact that we use more of them in a given charge. More powder = more gas to do the pushing. Pretty simple concept, but sometimes overlooked. Also, we have to consider the fact that not only does the bore volume increase as the bullet moves, but the barrel is cold. The gas behind the bullet cools a LOT from contact with that cold steel, and that also drops the pressure a lot (as Mr Boyle taught us).
Powders burn their best in a sometimes narrow pressure range. A given powder might burn very well as the pressure is rising, but if the combination of bullet movement, powder amount, temperature drop and other factors are such that the pressure never reaches that powder's "happy place" it may not all ignite or can even slow down its burn enough that unburned/partly burned kernels do in fact exit the muzzle. That's why it's best to say that the pressure peak signals the effective end of powder burn: about all the powder that WILL burn, has. Not all of it necessarily WILL burn, but all that can, does. And all that happens within a few inches of the breech, sometimes more, sometimes less - but not all the way down the bore.
C, I have shot a lot of CMP and kernals of unburnt and ,more so, partially burned or scorched powder,are clearly visible and in large quantity in front of the shooters.
That about all I have to say about that.
Continue on gentleman this is a really good thread,
Fans of Alliant 2400 will tell you that in less-than-maximum charges, they always find unburned powder flakes - sometimes enough of them to eventually jam up a revolver. The same is true of revolver loads using 4227, cast bullet rifle loads using 4350 or 4831 and several other examples. There are indoor ranges that have to sweep rather than vacuum their shooting lanes because a vacuum cleaner can ignite the large amounts of powder on the floor!
I would want to test the powder lot, and the rifle used, to check for unburned powder.
Is it surplus powder? how old?
Semi-auot rifle?
I use long barrels for my long range work, so I may never see unburnt powder. A short barreled rifle, or even "standard" length with a heavy bullet and slow powder,...... maybe. I don't shoot that way or in those venues. Mine is mainly benchrest/longrange hunting. A 26" barrel is about as short as I have, with some in the 30" park. I didn't beleive the article, so I took the 300RUM and stuffed it with an oooldddd batch of H870 and a 200gr pill. The H870 was sooo slow, that it might as well have been charcoal bricketts[:D] I don't recall the chrono readings, but after sooty necks and rediculously slow speeds, I checked the sheet and left. Keep in mind, this is a PacNor match grade tube with a tight chamber. The speed was several hundred FPS slower than H1000 or RL25. I saw nothing but white sheet. If I still had that magazine, I would post how to get a read on it[V] I didn't beleive it like you guys are saying, so I tried my best to test it, and found no unburned powder. You would think a 200gr pill with H870 in a cavernous case such as the RUM, would either prove or disprove that article.
and keep it scientific or experienced based, one more not so clever attempt at insults makes your data/info go the way of the dodo bird
We all have a choice here. We can believe what the college-degreed, professional ballisticians and engineers say about the topic, or we can believe what somebody on the internet says - me included. Spend an hour searching and reading things from somewhere other than chat boards. Much of what you find may be over your head, but you'll get the drift.
I don't gather much info from forums, unless it is linked to data (not someone's opinion of data). What I do like to do, is read books from trusted sources, such as "rifle accuracy facts" by Harold Vaughn (the grandfather of aerobalitics/flight mechanics technology base for nuclear ordnance at Sandia national laboratories) which I have read several times over the years. The data is highly involved and you gather more and more each time you re-read it. Also books like "precision shooting at 1000 yds" etc etc and my monthly copy of "precision shooting" which is courtesy of my membership to the "international benchrest shooters (IBS)". You see, I don't trust billybob and bubba on XYZ.com I take the claims/theory etc into the field, and try to prove or disprove it. It is something of a hobby, not to mention I just like to shoot. I can attempt to prove/disprove a theory, all while working up a load ladder or testing a drop chart, kind of a 2 for 1 range session. That is exactly what the 300RUM and H870 session was. I figured that much powder must produce higher MV, however it was just too slow.
if your bovine statement was simply "till the cows come home" and not directed toward anyone, then I take the blame for a misinterpretation
what do you write? Books? Newspaper?
(You must have "signatures" turned off. Like Ragu, It's In There!)
I have never had stiff bolt lift, or even flattened primers, but by the chrono, know I was well into the danger zone. This is one that has had me perplexed. I have a 6.5-06AI with a 26" tube, and used 140gr a-max pills and acheived 3208fps (according to the chrono). That was wayyyyyy toooo much speed for that case. Yes the primer pockets were loosened, but there were ZERO signs of over-pressure. To this day, I still am having issues since none of the traditional signs ever presented. You have any thoughts?? That is also the reason you will see me advocating the use of a chrono with AI loads. I don't get it,...how can you run them that hot, and NOT see pressure signs. You have the strain guage, so I ask for your interpretation as to why the AI does this.
This is only my opinion, with no solid proof.
Same reason you can get well into the "danger zone" with match chambers, that being the closer/tighter (min spec) chambers don't allow the case to expand as well as eliminating the "blow-by" of powder gas past the bullet.
The culprit is mostly the chamber. Near-parallel chamber walls don't allow the cartridge to expand rearward as much as tapered walls. So you won't see hard bolt lift or hard extraction. By the time there's enough pressure to expand the case head itself and loosen the primer pocket, pressures are well over 70,000 psi. That is DEEPLY into the safety margin designed into the gun, and is perilously close to the elastic limit of the brass itself.
A well-proven rule of thumb is that velocity is proportional to one fourth the percentage change of case volume. So, if you blow out a cartridge enough to get a 12% increase in volume (which is a huge amount; most AI rounds are closer to 8% larger) you should see about a 3% gain in velocity - AT THE SAME PEAK PRESSURE, all other things being equal. So a standard round that gets 2800 fps will get a whopping 2884 when blown out to the max. Get more than that and you are also running at MUCH higher pressure.
I have a quote somewhere in my files that says "Improved" is a terrible choice of words for these cartridges because it implies that they are better when most of them aren't much better if at all. Who said that? Parker Otto Ackley.
Thanks for those ideas fellas, I have been wondering about that for years.
also why my 300RUM hit a max load of 88gr H1000 and great accuracy (200gr SMK) but on a hot day, the next step of 89gr and I had to smack the bolt open. Tossed the rest in the ditch and went back to the 88gr load. That BTW was far under max in the data/books, but with a match chamber things changed drasticaly. From a smooth, easy bolt lift, to wayyy stiff in 1gr[:0]
It isn't air temperature that launches pressures to the stratosphere, it's GUN temperature. A hot chamber almost instantly transfers heat to the brass (which is an extremely good conductor). That not only raises the powder temperature, but partially softens the brass itself. Result? More brass stretching and thus hard bolt lift and hard extraction. The hot powder burns faster - it's a chemical reaction, after all - and that creates more pressure sooner, as well. Double whammy.
you ever done the full work up on Ackley Improved cartridges?? I would like your data or interpretation as to why they show no pressure signs until they are wayyyyy hot.
I have never had stiff bolt lift, or even flattened primers, but by the chrono, know I was well into the danger zone. This is one that has had me perplexed. I have a 6.5-06AI with a 26" tube, and used 140gr a-max pills and acheived 3208fps (according to the chrono). That was wayyyyyy toooo much speed for that case. Yes the primer pockets were loosened, but there were ZERO signs of over-pressure. To this day, I still am having issues since none of the traditional signs ever presented. You have any thoughts?? That is also the reason you will see me advocating the use of a chrono with AI loads. I don't get it,...how can you run them that hot, and NOT see pressure signs. You have the strain guage, so I ask for your interpretation as to why the AI does this.
Two reasons. The first is, as noted, the whole reason Ackley started improving cartridges. By straightening out the case walls they get a better grip on the chamber and hold more pressure. Working up loads the standard way, i.e. looking for flattened primers, bolt lift etc., is not the way to safely work up an Ackley load. There are small tell-tale signs such as case coloration around the web. If the burn coloration (faintly flakey looking, lighter colored) goes lower than the webs upper rim you are too hot. But, that's not easy to see. The best way is to go by chronographed velocity.
The second is flow vs. pressure or the 40 degree shoulder. Think of it like a water dam. When the gates are open like a 30-06 and 30-30 you don't tend to build pressure as quickly. Understand "quickly" is a misnomer here, we're measuring microseconds. Quickly is actually understood as measurement between loads. When the gates are more closed, like Ackleys, the pressure is going to build more quickly. Add to that when pressure increases on powder it burns faster producing more pressure. A bootstrapping effect. That's why with a heavy bullet and a bit too much slow powder it burns as though it was 4198.
I know that the 40 degree shoulder is Ackley's signature thing, kind of but I would look to maximizing the potential of each cartridge by changing that angle as needed.
Again, FWIW, the point of improving a cartridge is to gain something. So you can go higher in pressure. I like the Ackley cartridges and other improved cartridges simply for the reason you can boost pressure a little bit, and if you don't overdo it actually get longer life out of your cases. All the guys I know who shoot competition use them for that reason. Not so much added velocity.
A little bit is 100-200 (maybe) fps. Then stop. They are not running blindfolded towards a cliff if they stop when they need to. Most of us have gone through a phase where everything has to be as fast as you can absolutely load it with standard cases. Ackleys are no different.
You run a few ladders up. If you start to get any increase in the case color issue, past the point of velocity you hoped to attain, or slight growth of the primer pockets, then you stop. Or use a slower powder then try again.
I like the brass life, which is why I have chambered some barrels in AI. (6.5x55, 6.5-06 and 280) I have really been toying with a 1:7 or 1:6.5 twist, 3 groove, 220swiftAI. That should adequately launch the 80-90gr pills to 1000yds.[8D]
There's a guy on another forum who has no clue what his pressures are and says he doesn't care. His loads are safe, he says, because none of his rifles have blown up. He claims to be getting more than the standard 22-250 round can get - but still thinks his 223AI is safe. And nothing I can say will convince him otherwise. Oh well.