We all know what a typical chamber pressure plots look like, pic related.We also know that the bullet energy is basically the area under the plot.Now, why don't we make a combination powder with fast + slow powder so instead of a triangular shape the pressure curve looks more like a rectangle? This way we can maintain high chamber pressures all the way until the muzzle. We could achieve significant area under the curve increases with this, as much as +50% compared to traditional powders that have very little pressure left over by the time the bullet gets to the muzzle.
>>64738767>Now, why don't we make a combination powder with fast + slow powder>What is modern double base propellantsAnon you understand that triple and polybase propellants are actually experimented on, right?
>>64738767>make a combination powder with fast + slow powderBack in the day before we had the selection of powders we have today people did exactly that. go read up on the original .454 Casull load, it was a layering of 3 different powders in the case.Nowadays we engineer powders to have different burn profiles. It's more complicated than just "fast" vs "slow". Look closely at smokeless "powder" and it's not really powder at all, it's tiny little flakes, spheres, donuts, sticks, lobed sticks, hollow tubes, or other funny little shapes. It also has coatings on it. All of that is done to give it the right combination of "fast" and "slow" for a given purpose.
>>64738767https://en.citizendium.org/wiki/Gunpowder
>>64738767We already try to do that. We're trying our best okay? This is the best we can do with current technology. We all know a horizontal line is the holy grail, but it's just not possible right now.
>>64738890Look, all I want is an actual good reason to use 20'' barrels, please make it happen.
>>64739110You have them already. Double base powders are dead common, triple base powders are less common but still available, and some boutique ammunition manufacturers use duplex powder charges.
>>64738767Part of it is that the amount of energy you can get is based on the amount of powder you can fit into the cartridge. I don't think you can flatten out the curve without reducing the peak height unless you start using more energetically dense materials than nitrocellulose. The other issue is that as the bullet moves down the bore, the available volume increases, and it becomes increasingly difficult to create high pressures.I think tricks you can play like double/triple based powders or mixing powders can only stretch the curve a bit. I think if you really wanted to push things further, you'd probably need a fundamentally different propellant and a fundamentally different way to modify its decomposition.
>>64738767im pretty sure a pressure chart will always look like this simply because of physics the pressure spike isnt from the rate of powder burning, but due to it being confined in the sealed cartridge. as the bullet flies down the barrel the pressure gets lower because the combustion volume increasesif you want the same pressure the entire time the bullet is in the barrel, youd need way more propellant and it would somehow have to burn at a linear rate. something like a potato gun but its a cartridge
>>64740306RDX and other high energy propellants are already a thing, just not for civvies. Some real black magic goes into stupidly high performance autocannon rounds like the 25mm Bushmaster sabots.>Barrel burner>Do all sorts of flame temperature lowering and protective coating for barrel>Barrel life goes way the fuck back up
>>64740448HMX might work too. I imagine the carveouts for smokeless powder in the law is the main reason they haven't gotten too creative with the powder composition. That, or the cost (r&d and feedstock costs) are too big of a disincentive.
>>64738767if the bullet velocity is the integral of pressure, shouldn't the graph look something like this?
>>64741506no
>>64741506holy instantaneous acceleration batmanwe breaking the laws of physics here
>energy is the area under the curve Consider a 308 and a 6.5CM. Assume they are identical in every way except bullet diameter. Same powder charge, same Pmax. The 6.5 will sweep less volume as it moves down the barrel and so the pressure will remain higher for longer compared to the 308. So this would imply the 6.5CM has more energy. But it doesn’t, it would have less on account of its higher relative capacity.Or is it the area under the curve as long as powder charge and bore diameter are kept constant?
>>64740448You think the new meta of 80kpsi cartridges will prompt further development, refinement, and mass production of stellite-lined barrels? IIRC those increase barrel life by 1.5-2x, but they cost thousands per barrel to manufacture.
>>64741783Physical vapor deposition (typically with tantalum) is the new barrel life meta. The USN now uses it for their 5" guns. Same class of improvement but it's much cheaper and doesn't have size scaling limits.
>>64738890>We all know a horizontal line is the holy grailIt's really not.
>>64741780>The 6.5 will sweep less volume as it moves down the barrel and so the pressure will remain higher for longer compared to the 308. So this would imply the 6.5CM has more energyForce is pressure/area, anon...
>>64738859IIRC, the .454 triplex load only pulled an extra 100 fps over AA#9. Doesn't seem worth the squeeze when it comes to the extremely fucky process of mixing powders.
>>64741780Oops my bad.t. OP
>>64741873Yeah it really wasn't worth it which is why nobody does it today.There are a handful of times when people do mix powders but they are oddball niches. I know of three:1) People shooting scheutzen matches, usually with muzzleloaders, often add a bit of smokeless to an otherwise black powder load. The purpose is to reduce fouling. There are even special powder measures used for this which simultaneously dispense both powders. (picrel)2) Antique double rifles were often regulated using Curtiss & Harvey black powder. That was a common brand in the 19th century but is gone today, and it was hotter than modern black powder. People handloading for those guns often add a small amount of smokeless to weaker modern BP to make up the difference, which may be necessary to get a load which allows both barrels to shoot to the same POI.3) Very large smokeless cartridges, like the various .577 and larger dangerous game cartridges can have sketchy ignition and hangfires even with magnum large rifle primers. A common solution for that is to put a few grains of 4F or some fast pistol powder down against the primer to make sure you get good ignition.
>>64739110>actual good reason to use 20'' barrels,The reason is it allows you to get the highest velocity with the most complete combustion and most efficient use of powder.
>>64742015Sure, but it would also help if we could retain some more pressure for those last six inches.
>>64741819Yeah that’s why I was asking for clarification about energy being the area under the curve
>>64741755...explain?
