This might be a better subject for this forum and there might be more here who can point me in the direction I want to go.

Basically I am a knife maker and a welding inspector. When I came to knife making I hit the forums for information on how to start and then a single engineer came in and caused a huge shift by actually doing industry standard testing and showed that what I had thought to be an expert body of knowledge was completely outdated and has caused a huge increase in performance in especially the last 5 years. We are now aware of how huge performance gains can be gained by very carefully building a blade as well as how huge the gains have been in steel making. Given that the 65kpsi pressure limits were safe for production guns 100 years ago I find it funny how critical people have been about a minor increase in pressure and it got me started on a path to wanting to turn my attention to trying to build as high of performance firearm within civilian legal limits. I'm not concerned with action type but just if every single stop was pulled out from chamber and cartridge design and the down say an 18" barrel. I have an understanding of the basic ideas but finding any sort of reference material is hard. For any who who aren't sure what I am trying to do it's to run the pressure limits as high as possible and then to try to hold the maximum pressure curve in any possible way where I can get proper propellent burn and then to reduce friction, conserve heat while maximizing pushing forces.

OP, you say you want maximum performance yet only an 18" barrel? It doesn't work that way, you will have a hard time even getting with in the same area of performance with an 18" barrel, especially if you're going to hold it to a short action cartridge, even with that you will still give up performance with a long action cartridge but it will be easier to get "ok" performance  but not even close to high performance...If you truly are wanting max performance, you are going to need the biggest magnum cartridge out there as well as a strong long action  action, and a long barrel...Ideally the cartridge you are going to want is likely a wild cat, such as the Enabler line, it  burns over a 150 grains of powder  to launch a 400 grain .375 bullet at over 3200 fps...The problem with wild cats is it's a lot of effort to produce usable brass......over the counter top performance, you might look at 50BMG(accuracy May be a tough find) or one of the cheytacs.. or other like lazarony, or a few others I can't think of right now...Otherwise you can look at 338LM, 338 edge,30-378 Weatherby, 300rum, 7mm rum, or a few others..
I shoot the 300 rum, its my ELR/hunting rifle...I use a tenacity action, a 30" Bartlien 9 twist barrel, an MPA chassis and I currently load the 230 grain berger hybrid target bullet, with RL-33 powder that produces 3220fps velocity with 5300 energy...This bullet runs .389 G7 BC.. I am getting ready to do load work on the new 245 grain 30 cal, Berger hybrid target, it runs .433 G7 BC..I am hoping for over 3100 fps...
You do know it's much harder to shoot the big magnums? they are also prone to fast barrel wear, especially rods like 7mm rum where you have big over bored cases necked down to a smaller bullet..

I guess I should add that I have a good understanding of reloading but it starts to fail when we get to the limits and deeper technical details of propellent. And obvious first thing to head for is sabots fin rounds and smooth bores? From what I understand max velocity will be limited by the speed of sound of the gas at that pressure  so higher pressure both means faster acceleration and hopefully a longer period of full pressure. The downside of cartridges is that with the powder at the base and as the bullet moves down the bore it creates a larger burn chamber and drops the pressure and that means the heat drops of as well and it is further being lost. I gather it's probably hard to actually do but a "traveling charge" is added the gas production doesn't have to push against the weight column but instead is pushing back against it and gets lighter as it moves down to bore. A tapered or squeeze bore can also be used to increase pressure as it moves down the bore. My thought is that a special cartridge would need to be made and done in a way where it was more rebuildible than reloadable. I don't know if this a realistic theory or not but if the primer went to a central chamber that could be loaded with a very fast burn powder to kick off the pressure curve and then to start ignition for the main charge. My next thought was that a 3D printed cartridge that would both insulate and then allow for a progressively slower burning powders. Then the sabot would hopefully would contain a slower burning propellent and perhaps if it isn't possible to keep pressure high enough to keep smokeless powders burning correctly then a solid fuel like what is used in rockets might work to help keep heat and pressure as high as possible.

You envision a cartridge that have some of the Sig Fury round features at higher pressure, the steel case head, and a sabot flechette projectile, similar to some of the prototypes from the 70's, and add in some of the effect of the Gyrojet to burn the propellant attached to the sabot?

So how high can the pressure be? Sig Fury is 70000-80000 psi? Steel case head and primer, can a chamber / action be developed to contain 150000 psi or what is the material limit. 50-60 thousand psi was the technology / material limit from early 1900's

How to level the pressure curve by having the propellent travel with the payload, generating the gas at a progressive rate as the payload travels down the bore keeping the pressure curve flat entire time payload is in the bore. propellent shaped like a hollow tube burning from the center generating gas from a progressively large area as the propellent grain burns.?? Less heating of the action since the source of the heat is moving down the bore, leaving high pressure gas behind, highest heat / pressure at the muzzle end ???  

You aren't the first person wanting to reinvent the wheel.

Barrels are a wear item. Even with a massive receiver and heaviest barrel, the barrel's throat on any firearm would be destroyed in short order. "Ultra-high performance" comes with a cost. .243 match rifle barrels are only expected to last around 1000 rounds. Do you think that is a reasonable investment at $500+ a pop?

Most popular calibers are popular, because they are very accurate and have a long service life. .308 can be expected to give good accuracy for around 5000 rounds, .223 as well. High velocity, and especially heat, will destroy barrels quickly.

There is no such thing as a free lunch.

I believe the issue is less about the action/receivers and more along the lines of cartridge design.

It doesn’t matter if the barrel and receiver hold up if you’re having case failures and leaving parts of the case in the chamber after each shot or fouling the firing pin/ejectors with brass shavings.

Trying to get maximum performance with an 18” barrel by nuking a cartridge doesn’t seem like the way to go. I’d wait to see how the .277 Fury does first, with its expensive cased ammo. While this may work, I don’t see it as being a trend for ppl purchasing their own ammo. It’s bordering on cost prohibitive.

Running longer barrels with an appropriate powder for the bullet weight is the current “best practice” to up performance, but hey, hopefully you’ll come up with something.

That's really not the direction I was going. I'm talking about increasing performance not velocity although one may want to do both. A standard cartridge for high velocity would use a slow burn powder that will take longer to come up to pressure. If you take it to the normal max of say 65kpsi thw bullet moves forward creating a larger gas reservoir before it really begins to burn and then it's done and you are working from dropping pressure all the way out and if you keep adding more propellent until it weighs more then the projectile you are pushing it down the barrel as well and it doesn't get any lighter even though as the pressure drops so does heat so you lose pressure from the gas extra fast and riflings is going to drain energy as well. Just the brass in the case is going to suck the heat out of a big part of your fuel and it does nothing but provide recoil. With very over bored cartridges you are also getting recoil from both the large weight of propellent and then the rocket effect from all the gas exiting. My most practical use for the rifle or firearm might be for and ultra-lite backpacking rifle.

Something a bit less ambitious might be to use gain twist rifling on a large bore rifle like a 30-06 case somewhere between a 35 Wheel  and straight walls. With use of a sabot you can shoot any caliber out of it and you only need a short barrel since there isn't enough gas volume in the case to make a long barrel worth it. Just with the larger area to push on as well as loosing less heat to the walls and using faster powders you are going to get more energy. The gain twist rifling would be just to both reduce some friction but also have much faster twist rates than is standard for the bore so smaller caliber high bc bullets will stabilize. For that you just need a sabot that works.

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That's kinda what I was thinking. I have read about something in a development in a short article that I later read was actually a leak that had most of these features and ran at something like 150kpsi. From what I have read powder is a problem. At some point it's going to detonate. Really I think understanding propellent at a higher level is going to be where I think people can help me the most and give reading recommendations.

I am far from the first on this. Most of the reasons that the others in the past didn't take off was that it would have to high of cost at some level. There is also coming out with a whole new type of ammunition. Some things like sabots I think we're going to be difficult in the past but I'm hoping that with 3D printing they might actually be one of the easiest parts. The other part about cost I think is the reason why you do it. I'm going to dump $400-500 into a very plain looking knife for myself. I had to buy several grand in equipment to do it and it's not like I can't find something cheaper to cut with. I just wanted to make the highest performance knife possible. Will this one be ? Of course not but it's the best I can do right now and better than anything in production and better than some handmade knives and for others maybe it depends what we call better and higher performance but one way or another it's something I wanted to do. A lot of this was tried a long time ago and we do have materials available now that they didn't then. There is currently ongoing research into something very similar but it's not like I am easily going to get my hands on it even if it does come out.

Some things I think people mistake where problems come from. Overbore rounds wear out barrels because of gas quantity not pressure. I'm sure pressure adds but it's the large volume of gas that has to run down a small bore that really starts to cut it. Most of this will be a large bore area and would use a smooth bore. I had actually thought that a multi piece bore would be best. From what I have read it's the forcing cones that wear and they should be something that can be replaced. Using wear resistant material for the bore would make sense. I think the reason for most barrel material is cost and ease of machining. higher pressure doesn't mean more gas and with sabots wear might not be as bad as one would think although there would be more heat.

So thinking of a open ended pressure vessel, with a removable cap, the barrel and chamber.
Get rid of the cartridge case, you need to assemble the projectile, propellent, and a ignition source. Ideally eject everything down the bore.
Make the sabot from brass like segmented cartridge case turned around with the bullet attached to the base and the open end filled with the popellent / primer, everything goes out the end of the barrel. (case / sabot combination of the pinfire and Gyrojet)?
Possibly use a laser mounted to breech inside chamber to ignite propellent, or electric arc, to eliminate the primer?
Sabot with conventional bullet with rifling, or a fin stabilized flechette smooth bore?

Thinking of the 120mm tank round, downsized, to shoulder fired, thnk they get +- 4000 fps? Only part ejected from breech is the rounds head about 6 inch tall??

OP, you need to learn to use the Quote button for your replies.

Thanks. I'm new to this forum.

Thank you for taking instruction.  It's been impossible to understand which post you were replying to.  

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