What makes a cartridge a high pressure cartridge?

[saturno_v]

Questions for the experts:


In my understanding, the factors (or combination of some of them) that influence how high pressure a cartridge is are:

- Powder quantity (obvious)

- Powder type

- Overbore ratio

- Case shape/design and case space/powder ratio

Am I missing something else? Is this correct?

I heard somewhere that in a very high pressure cartridge if you go below certain bulet weight you may actually decrease the velocity because the powder charge doesn't have the time to reach full pressure potential....true o fantasy?

Along the same line, it is a correct assumption that the shape of a bullet in any given cartridge may influence barrel speed because of variance in bearing surface? I heard also that a "too loose" bullet (very small bearing surface) may actually result in slower velocity because, again, the powder charge behind cannot reach peak value..true or false??

And if this is true (one or all of the instances) what are the difference in percentage? Negligible or noticeable?

Last point is this: We all know that you could have a higher pressure cartridge that may actually develop slower muzzle velocities than a lower pressure one even within the same caliber and bullet weight...I always assumed the difference would be that in the lower pressure cartridge, the powder charge would burn longer (because of quantity and/or powder characteristics and/or case design factors)....Am I correct?

A typical example is the comparison between 308 Winchester and 30-06 Springfield...the 308 is a higher pressure cartridge but it actually reaches slower muzzle velocities than the 30-06 (when both loaded to their full potential) even using the same identical bullet (weight and shape)....in this particular case why is so? What are the factors in play?


Thanks!!


Regards

 

[R.W.Dale]

The one and only thing that determines his high a pressure a cartridge is SAAMI specs.

- Powder type

- Overbore ratio

- Case shape/design and case space/powder ratio

Bore case ratio has nothing to do with it 460 & 500 Magnum operate at similar pressures to 300wm. Case strength also comes into play though, and an example there
s no reason 7x57 (51K psi) cant be loaded to 7mm-08 pressure (61K) in a strong action, bu no matter how strong the action try loading 30-30 past 42,000psi and youll have problems

I heard somewhere that in a very high pressure cartridge if you go below certain bulet weight you may actually decrease the velocity because the powder charge doesn't have the time to reach full pressure potential....true o fantasy?

I doubt it would happen i you used a propellant if the correct burnrate for the bullet weight. It might happen if you stuck with the same slow powders you used with heavy bullets

Along the same line, it is a correct assumption that the shape of a bullet in any given cartridge may influence barrel speed because of variance in bearing surface? I heard also that a "too loose" bullet (very small bearing surface) may actually result in slower velocity because, again, the powder charge behind cannot reach peak value..true or false??

Every barrel is different, getting into bullet shapes effect on pressure is really starting to split hairs. EXAMPLE. Going from .311 to undersized .308 bullets only created a velocity disparity of about 3% (see center sig link)

Last point is this: We all know that you could have a higher pressure cartridge that may actually develop slower muzzle velocities than a lower pressure one even within the same caliber and bullet weight...I always assumed the difference would be that in the lower pressure cartridge, the powder charge would burn longer (because of quantity and/or powder characteristics and/or case design factors)....Am I correct?

No

The only time a lower pressure cartridge will outperform a higher pressure cartridge is if the case volume is much bigger on the low pressure round. Same case volume different pressures the high pressure round will ALWAYS be fastest

A typical example is the comparison between 308 Winchester and 30-06 Springfield...the 308 is a higher pressure cartridge but it actually reaches slower muzzle velocities than the 30-06 (when both loaded to their full potential) even using the same identical bullet (weight and shape)....in this particular case why is so? What are the factors in play?

the pressure difference is only about 3% in favor of the 308
the case volume difference is about 18% in favor of the 30-06

 

[Art Eatman]

When the .308 first came out, the factory specs claimed a chamber pressure of some 55,000 psi (not CUP). The common factory loading for the '06 was around 49,000 psi because of its use in older rifles. It's no big deal whatsoever to load an '06 to 55,000 psi in any modern rifle; I've done that for almost sixty yearx. (Modern, I guess, being anything of post-WW II manufacture. But, it certainly holds for any 1917 Enfield or Model 70.)

SFAIK, the terms "high pressure" or "high intensity" came into use with pistol cartridges moreso than for rifle cartridges. The old .45 Colt, the .45ACP and the .38 Special pressures are around 12,000 psi or so, maybe 15,000, but when the .357 Maggie showed up, the chamber pressure came to be around 30,000 to 35,000. For rifles, almost all smokeless powder cartridges began life at around 40,000 psi.

40,000 psi is pretty much taken to be the upper limit for bolt-actions with one locking lug. Early Mausers; the Krag. And, for the Model 94 Winchester with its locking lugs at the rear of the bolt.

 

[saturno_v]

The common factory loading for the '06 was around 49,000 psi because of its use in older rifles. It's no big deal whatsoever to load an '06 to 55,000 psi in any modern rifle; I've done that for almost sixty yearx. (Modern, I guess, being anything of post-WW II manufacture. But, it certainly holds for any 1917 Enfield or Model 70.)

My gunsmith told me that my sporterized rechambered Mauser 98 can take any 30-06 loadings a modern rifle can take....do you think he is correct?
The action was manufactured for sure after 1933 (it has a swastika stamp on the receiver...unless has been restamped)

 

[saturno_v]

Krochus

So the only factore that increase the cartridge SAAMI pressure ratings is the powder quantity???

The only time a lower pressure cartridge will outperform a higher pressure cartridge is if the case volume is much bigger on the low pressure round. Same case volume different pressures the high pressure round will ALWAYS be fastest

What is the technical explanation for this??


Thanks

 

[R.W.Dale]

My gunsmith told me that my sporterized rechambered Mauser 98 can take any 30-06 loadings a modern rifle can take....do you think he is correct?
The action was manufactured for sure after 1933 (it has a swastika stamp on the receiver...unless has been restamped)

I would say he's coorect

IIRC 7.92x57mm loads used by the Germans in WWII were loaded to higher pressures than our 30-06

 

[rbernie]

Large ring Mausers have been used as a basis for many hi-pressure and large-bore magnums. The ring is large enough to ensure that the breech end of the barrel (which will be made of modern steel) is plenty thick.

 

[R.W.Dale]

Krochus

So the only factore that increase the cartridge SAAMI pressure ratings is the powder quantity???

No I didn't say that. SAAMI pressure ratings are just that MAX PRESSURE RATINGS established for safe factory loads for that particular cartridge, as a handloader there's any number of ways you can exceed these intentionally or unintentionally

 

[saturno_v]

Krochus

I understand that...I mean in layman terms how you increase a pressure in a cartridge (either as handloader of cartridge designer)?? Just increasing the powder charge?? Bore/case ratio, powder type are not in play???

In simple terms, the 7,62x39 is lower pressure than a 308 mainly only because it contains less powder???

 

[saturno_v]

Large ring Mausers have been used as a basis for many hi-pressure and large-bore magnums. The ring is large enough to ensure that the breech end of the barrel (which will be made of modern steel) is plenty thick.

That is what I thought and heard around...just wanted to confirm.

 

[rbernie]

In simple terms, the 7,62x39 is lower pressure than a 308 mainly only because it contains less powder???

Pressure is dictated by the volume of the vessel and the amount of gasses produced. You can increase pressure by making more gas (oxidize more gunpowder) or by making the vessel smaller for the same amount of gas. In your example, 308 is higher pressure because it makes more gas for it's internal volume than does the 7.62x39. In other words, even though the 308 case is larger it makes more than enough extra gas to cause its internal pressure to be higher.

 

[saturno_v]

Rbernie


Thank you...extremely clear.
If I recall correctly, when you load a cartridge you need to leave some empty space (the amount depending on the type of powder) in the case...you cannot load the case "to the hilt" where the powder basically touches the bullet....it is true??

Maybe not because I heard the term "compressed load"...what is that??

 

[saturno_v]

Krochus


So I guess that a lower pressure cartridge can outperform in velocity a higher pressure one if it produces more gas (due to the bigger case) to push the bullet.

An extreme example: a 357 SIG has a SAAMI pressure rating of 40.000 psi while the 30-30 is at 42.000 psi

However I doubt that even in a carbine barrel a 357 SIG can push its 125 gr. bullet at the same velocity a 30-30 can spit a 170 gr. pill from the same barrel length...am I right??

 

[R.W.Dale]

In simple terms, the 7,62x39 is lower pressure than a 308 mainly only because it contains less powder??

NO

the amount of powder is only part of the story. You can load 7.62x39 to 308 pressures but not using the same powders 308 does.

You can either

A. add more powder, but the case is only so big and only holds so much
B. go to a less "bulky" propellant that's also typically faster that allows you to fit enough inside the case to reach whatever max pressure you're shooting for. But too fast and pressure will spike beyond reason before the bullet can start to get out of the way by traveling down the bbl


22-250 Remington and 300 Wby Mag both share the same 65,000 PSI SAAMI max pressure rating. The Weatherby probably holds 3 times the powder 22-250 does

 

[jim in Anchorage]

Compressed loads are just that-the seating press forces the bullet into the[full] neck, compressing the powder. Very common with slow burning stick powders in bottle neck cases.

 

[R.W.Dale]

Krochus


So I guess that a lower pressure cartridge can outperform in velocity a higher pressure one if it produces more gas (due to the bigger case) to push the bullet.

An extreme example: a 357 SIG has a SAAMI pressure rating of 40.000 psi while the 30-30 is at 42.000 psi

However I doubt that even in a carbine barrel a 357 SIG can push its 125 gr. bullet at the same velocity a 30-30 can spit a 170 gr. pill from the same barrel length...am I right??

Now you're on the right track. If the pressure disparity is small enough between the two cartridges and the case capacity difference is large enough in favor of the lower pressure round than it's POSSIBLE to out perform the cartridge with the higher pressure rating.

But if everything is equal with regards to case capacity than the high pressure cartridge will always come out on top

or to put it the other way comparing two cartridges with the same pressure rating the one with the most case capacity will win

 

[saturno_v]

Krochus

B. go to a less "bulky" propellant that's also typically faster that allows you to fit enough inside the case to reach whatever max pressure you're shooting for. But too fast and pressure will spike beyond reason before the bullet can start to get out of the way by traveling down the bbl

That is the reason why overbore cartridges (some are more than others) require more slow burning powder right??

The so called "pistol powders" (they burn faster) are incidentally used in short straight walled cartridges...am I correct???

22-250 Remington and 300 Wby Mag both share the same 65,000 PSI SAAMI max pressure rating. The Weatherby probably holds 3 times the powder 22-250 does

The 300 Wby uses a more slow burnign powder, that's why it needs longer barrels to reach its full potential...right?? At 24" the 300 Wby performance falls to the level of a regular 300 Win Mag.


Thanks

 

[R.W.Dale]

The 300 Wby uses a more slow burnign powder, that's why it needs longer barrels to reach its full potential...right?? At 24" the 300 Wby performance falls to the level of a regular 300 Win Mag.

Now you're getting into a different mythology, the tale of burnrate being tied to bbl length
http://www.thehighroad.org/showthread.php?t=480593&highlight=powder+burnrate+length
NO

300 wby still holds all the cards over 300wm in two identical 24" bbls, higher pressure and more case capacity and therefore will still be fastest

 

[saturno_v]

But if everything is equal with regards to case capacity than the high pressure cartridge will always come out on top

The higher the pressure, the higher the temperature.....the pressure wave (which push the bullet) cannot exceed the speed of the sound in that gas at that temperature (the higher the temperature the fastest is the speed of sound in that gas)

The famous performance ceiling of traditional chemical propellents....if I remember correctly the theoretical limit is around 2000 meters per second (about 6600 fps) but in reality you cannot reach it for several other reasons

 

[benzy2]

Rbernie


Thank you...extremely clear.
If I recall correctly, when you load a cartridge you need to leave some empty space (the amount depending on the type of powder) in the case...you cannot load the case "to the hilt" where the powder basically touches the bullet....it is true??

Maybe not because I heard the term "compressed load"...what is that??

Burn rate matters as well. Compressed loads are exactly that. The powder charge filled so full that the bullet actually compresses the powder charge when the bullet is seated. Some powders in the right cases with the right bullet weights can't fill a case full enough to be over pressurized. Some people don't like to run compressed loads. I believe you get less consistent powder burn the more compressed a load gets but don't quote me on that. I have always been told that the most accurate loads tend to be those where the powder charge is from about 90-95%+ full.

 

[saturno_v]

Krochus


I heard from handloaders that 300 WBY and 300 Win Mag are almost equivalent at their full potential in a 24" barrel...yes there may be a difference of 150 or 200 ft/lb of ME but that's it

Even if you look at the published numbers from Remington and Federal for the 300 Wby (they use 24" test barrels) they are not that dissimilar from their 300 Win Mag offering.

I'm not saying they are exactly equal but for all practical purposes they are almosty ballistic twins in a shorter barrel.

Even a Weatherby technician admitted that in a Vanguard (24" barrel) is more practical to stick to the 300 Win Mag.

Edit:

Krochus I did check your link and I think I understadn what you mean....if you take a 26" barrel on a 300 WM the difference would not as dramatic as well.


Many people think that the 300 WBY is such a better performer because they read the Weatherby published numbers for the cartridge, which are intended for 26" barrels, then compare them to the 300 WM from the major ammo manufacturers which are intended for 24" barrels.

 

[jim in Anchorage]

Burn rate matters as well. Compressed loads are exactly that. The powder charge filled so full that the bullet actually compresses the powder charge when the bullet is seated. Some powders in the right cases with the right bullet weights can't fill a case full enough to be over pressurized

I knew no one reads my posts:banghead: See # 15

 

[saturno_v]

B. go to a less "bulky" propellant that's also typically faster that allows you to fit enough inside the case to reach whatever max pressure you're shooting for. But too fast and pressure will spike beyond reason before the bullet can start to get out of the way by traveling down the bbl

So powder type and the case shape affect pressure.....you can have pressure spikes in a overbored cartridges with the same powder charge compared to a straight walled one....the gases are more constrained...or ifyou use a too fast burning powder...

 

[benzy2]

I knew no one reads my posts See # 15

No need to get mad about it. Between typing slow and a few other distractions your post wasn't posted when I started my response.

 

[saturno_v]

Krochus


I did talk with a Hornady technician a while ago regarding their light Magnum 30-06 loads, I asked if they were safe to shoot in my Mauser 98 then we entered an interesting technical discussion, the guy was very friendly.

He told me that the max peak pressure of their Light Magnum loads is actually lower than the hottest SAAMI compliant loads, just they use a proprietary extremely slow burning powder...he also told me to do not bother using these loads on a 22" barrel as the performance would fall to the same level as any Remchesteral loads from the same 22 " pipe.


So I see you point that a higher pressure load will always attain more velocity regardless of barrel length but it seems to me that the extra barrel length allow some magnum cartridges using very slow burning propellents to pull ahead even more....


Going back to our comparison between the 300 Wby and the 300 WM, yes it is true that in a 24" the 300 Wby is still "technically" ahead of the 300 WM even if by only a couple of hair, but in a 26" (for both cartridges) the Weatherby round would pull ahead even more....the performance delta would increase.

If this wasn't the case, there would be no reason for some of the modern super magnums to have barrel length in excess of 28"....