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Old February 8, 2013, 09:26 PM   #1
Palmetto-Pride
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A pressure question I have been wanting to ask for a long time.

So hear me out on this one it may be long.

Ok here is my question/theory lets take a Remington 700 heavy barrel they range in calibers from .223 to 300win mag or better yet lets stay with 30 caliber and the same bullet weight lets say 110grain from 300 BLK to 300 win mag, what determines there maximum velocity is the amount of pressure pushing the bullet what determines the amount of pressure pushing the bullet is how much powder is burned correct? Ok now lets go to the barrel a 300 BLK barrel is essentially the same as a 300 WIN MAG from the throat to the muzzle what makes it different is how big the chamber is cut correct? So you could take a 300BLK and re chamber it to 300 WIN MAG. So here is the meat of my question. If the same barrel can withstand the pressure from 300 BLK to 300 WIN MAG why couldn't you take a smaller cartridge like 308 WIN and put a powder charge behind it equivalent to 30-06 or bigger, or take a 300BLK and put a powder charge behind it that would be equivalent to 308 WIN. I am asking this with the hypothesis that such a super powder exist. In short what if you could push a 168 grain bullet from a 300BLK as fast as a 308WIN could push it. That would turn the AR-15 into one hell of a weapon would it not?
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Old February 8, 2013, 09:45 PM   #2
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My very simple answer would be that the amount of powder needed to reach those pressures wouldn't fit in those cases.
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Old February 8, 2013, 09:46 PM   #3
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Powder capacity = case volume; and powder/case compatibility.
300 Win Mag has a much higher case capacity than 308 or 7.62x39 or 30 cal carbine.
That case capacity is then packed with more of a slower burning powder, to push a heavier bullet much faster.
You cant duplicate 300 W Mag with a 30 cal carbine. That capacity also tends to make for a longer cartridge, which means a longer action/receiver. AND, that longer action is rated for the heavier duty cartridge.
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Old February 8, 2013, 10:06 PM   #4
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Pressure is not the goal.

It is pressure over an extended period of time/distance = Work Energy

That Energy is contained in the amount of powder you have to burn to maintain that pressure, while simultaneously not exceeding max pressure.

Case volume then comes into play -- and here's a case (no pun intended) where sized matters.
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Old February 8, 2013, 10:21 PM   #5
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The bullet energy is the force times distance.
That is a function of average pressure... minus friction.
The peak pressure cannot exceed the strength of the brass... the weak link.
The large capacity cartridges can have a higher average pressure without exceeding the maximum pressure.
So large capacity cartridges can get higher bullet energies.
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Old February 8, 2013, 10:29 PM   #6
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Quote:
...or take a 300BLK and put a powder charge behind it that would be equivalent to 308 WIN.
As case capacity decreases, a given amount of powder will produce higher pressures.

Assuming you could get it to fit, putting a powder charge from a large case in a small case would result in higher pressures in the smaller case than it did in the larger case.

This is why bullet setback is a serious issue in some pistol cartridges. A safe powder charge can result in dangerously high pressures if the bullet is pushed back (set back) into the case significantly during the chambering (or rechambering) process. Pushing the bullet deeper into the case reduces the effective capacity of the case and that drives the pressures up for a given amount of powder.
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Old February 8, 2013, 10:47 PM   #7
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Thanks for all the replies, but what if you could get a special powder that would produce the same pressure in a smaller case that would push a bullet faster than in a larger case.

I will ask in a simpler way. Would it be possible to push a 168gr 30 caliber bullet at say 2700-3000 FPS from a case as small as 300BLK if there was a powder that would produce the pressure without the barrel blowing up?
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Old February 8, 2013, 11:18 PM   #8
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Palmetto-Pride, with the right chemistry, any powder could do anything. We just ain't there yet. But some folks are working on it; probably.

The problem with small cases is they don't hold enough powder to keep pressure up high enough for longer barrels to benefit from. At least with the smokeless propellants available today. It's all 'cause of the expansion ratio of the powders used. You can't get enough powder in a 30 Luger (7.65×21mm Parabellum) case to push its 93 grain bullet out of a 24 inch barrel at 3400 fps like a .30-06 can. It's tiny powder charge doesn't expand enough as a gas to do it safely. Maybe in 27 years there'll be a powder to do that.
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Old February 9, 2013, 12:17 AM   #9
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Right now the best commonly available powder for that combo would be Ramshot X-Terminator.
But even it can't quite get ~2,000fps and throws almost 10% of the powder out of the end
of a 20" barrel un-burned.


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Old February 9, 2013, 12:56 AM   #10
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Quote:
Thanks for all the replies, but what if you could get a special powder that would produce the same pressure in a smaller case that would push a bullet faster than in a larger case.
You pretty much already ARE producing the same pressure in a smaller case. The problem is that you run out of powder quicker because there is less of it to burn. Because you run out of power more quickly, the area under the pressure curve is less and that means the total amount of force applied to the bullet before it leaves the bore will be less. That means lower muzzle velocity.
Quote:
Would it be possible to push a 168gr 30 caliber bullet at say 2700-3000 FPS from a case as small as 300BLK if there was a powder that would produce the pressure without the barrel blowing up?
The problem is that there is a practical limit to how much pressure the system (case & gun) will tolerate. If there weren't any limits on the pressure, then you could do a lot of things that are currently impossible.

Questions with an "if" in them are problematic when the "if" is followed by something that's not possible.
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Old February 9, 2013, 09:59 AM   #11
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Quote:
I will ask in a simpler way. Would it be possible to push a 168gr 30 caliber bullet at say 2700-3000 FPS from a case as small as 300BLK if there was a powder that would produce the pressure without the barrel blowing up?
Theoretically this could be done, but probably not with actual gunpowder. The military has dabbled with using high explosive as a propellant and velocities as high as 20,000 fps have been achieved in comparison, smokeless powder's absolute maximum is around 6,000 fps and I know of no cartridge achieving more than 4,800 or so. Such a propellant, with so much more energy potential than smokeless powder, could be used to give something like a Blackout extremely high velocities, if properly formulated, and if pressure issues could be overcome. And of course, the cost issue.

Just a small disclaimer: If you pack a cartridge case full of C4 and set it off I am not liable.
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Old February 9, 2013, 10:53 AM   #12
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I suggest a railgun.
That would solve the problem.
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Old February 9, 2013, 11:27 AM   #13
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Hey guys thanks for all the replies I love this fourm for picking other people's brain who are smarter than me...

I guees you all see where I was going with this, I was thinking what a weopon a 300BLK would be if it could push 30 caliber bullets at 308 speeds.

Hornady's 300 Whisper/Blackout 110gr Vmax Supersonic load @ 2375 fps - 16" Bbl

I wonder if they could make a "Superformance" load out of this and get another 200FPS that would put it at 2575 fps that's what a 308 would put it at at around 200yds out of a 24" barrel.
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Old February 9, 2013, 12:55 PM   #14
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You want to be at near peak pressure for as long as possible during the burn time to achieve high velocity.
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Old February 9, 2013, 01:29 PM   #15
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Quote:
mehavey
I suggest a railgun.
That would solve the problem.
The rail gun was a Reagan era parlor trick that many in the defense biz got paraded past.
Rail guns were either capacitor discharge or rotating disc discharge.
I know some guys who bought the surplus rail gun equipment for less than pennies on the dollar.
At that warehouse amateur lab, the rail gun concept did not work as well as the steam gun concept, using the same low ESR low ESL high value high Voltage capacitor bank. We charged it with a neon sign transformer and diode stack.
That was back in the 1990s, but I still have some shrunken coins from the steam gun experiments.
Wrap a wire around a coin and put a million Amps through the wire. The wire explodes into bullet like pieces, and the coin gets an eddy current that makes a magnetic field that interacts with the magnetic field from the wire.
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Old February 9, 2013, 02:15 PM   #16
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Quote:
The rail gun was a Reagan era parlor trick that many in the defense biz got paraded past.
Oh yee of little faith....

http://www.smartplanet.com/blog/thin...;siu-container

> Phase I was focused on the development of launcher technology
> with adequate service life, development of reliable pulsed power
> technology and component risk reduction for the projectile.
>
> Phase II, which started in 2012, will advance the technology for
> transition to an acquisition program. Phase II technology efforts
> will concentrate on demonstrating a rep-rate fire capability.
http://www.onr.navy.mil/Media-Center...c-Railgun.aspx



.
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Old February 9, 2013, 05:02 PM   #17
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308 110 gr Sierra Varmitter gets 3300 fps using H335. That is 1000 fps difference you won't cover. 300 mag would be over 4000 I think.
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Old February 9, 2013, 05:25 PM   #18
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Mehavey,

They'll need to work on the aerodynamics of that projectile a little to get it out there 100 miles, but interesting to see it's feasible.


Palmetto-Pride,

The space under the seated bullet is over twice as much in the .308 Winchester as in the .300 Blackout. That means the .308 has room for potentially twice as much stored chemical energy, whatever powders you choose from. If you assume the energy transfers to the bullet from the powder with equal efficiency in both, the .308 Win then has the potential to impart twice the kinetic energy to the bullet. Kinetic energy is proportional to the square of velocity, and the square root of 2 is 1.4, so the .308 has the potential to produce 1.4 times as much velocity in the same weight bullet that the .300 Blackout does. In real life the efficiencies aren't identical and the .308 has a higher peak pressure spec, but still, the 1.4:1 velocity ratio isn't far off the mark.

If you formulate some kind of super powder for the .300 Blackout, then you can do the same for the .308 and you will still come back to that roughly 1.4:1 velocity difference.
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Old February 9, 2013, 10:25 PM   #19
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".. what if you could get a special powder that would produce the same pressure in a smaller case that would push a bullet faster than in a larger case."

Can't be done. Speed is much more than simply the pressure peak; it's the average pressure applied over time. We can get as much pressure as any action can withstand by using a small quanity of pistol powder but the pressure pulse would be too brief to accellerate a rifle bullet to any useful speed. Maintaining high average pressure while bullets accelerate down the bore requires a high volume of gas and the laws of physics tells us we can't get more out than we put into the case. If you want more speed, use more powder of a burn rate that can do the job - and there's a practical limit to that too.
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Old February 10, 2013, 11:19 PM   #20
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Quote:
Originally Posted by wncchester
We can get as much pressure as any action can withstand by using a small quanity of pistol powder but the pressure pulse would be too brief to accellerate a rifle bullet to any useful speed.
I think you're forgetting .22 Rimfire rounds. But you are right that maximum rifle velocities cannot be had from fast powders.
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Old February 11, 2013, 07:14 PM   #21
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I don't have much to contribute, seeing as our resident experts have it covered. Still, it might interest the OP to know that there are AR-15 variants available in 308Win. You don't have to abandon your dreams of 308 power out of an AR, and no magical gunpowder required!
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