Would a particular bullet (dia., style, weight, coating, etc.) driven at a particular chamber pressure give the same velocity in the same barrel?

The question sounds simple but I see some information that would indicate that the answer varies. The discussion about the relative merits of the short & fat powder column of the newer cartridge designs has me scratching my head and thinking that maybe there is something important I am missing. Is there perhaps some way to try out the same (safe pressure) load in both rounds to see if in fact the same velocity is derived. Maybe something along the lines of comparing the 30-06 case to the 300 WSM case when both are loaded with the same amount of the same powder. I know that the same powder is not optimum for both, but for this discussion I am trying to figure out if the shorter powder column does actually burn more efficiently.
A load of 59 grains of RL 19 is listed as max. for the 30-06 with a 165 grain bullet, so if loading 59 grains of RL 19 in the 300 WSM would be within allowable pressure limits then testing that powder load with the same bullet and same barrel configuration should derive the same velocity.
This may be a bit hard to follow but is the essence of my question.

I understand that to make a true apples to apples comparison you would have to have two cases with exact same capacity and test them in the same barrel using the same components, but I do not see any place that this has been done. Perhaps this is an old discussion and somebody already has the answer and I am just out of the loop. If so I would appreciate being brought up to date. It also might just be that the 300 Remington Short Magnum or 7mm Remington Short Magnum that are just being announced have a case capacity similar to some existing long/skinny round so that a valid comparison could be made.

This question has ignored the use of optimum powder for both situations and anybody who reloads knows very well that choosing the correct powder is very important and perhaps that is where this discussion should actually be pointed. I am not knowledgable enough to know, but am very interested in the answers.

[This message has been edited by Bruce Gordon (edited 08-27-2001).]

Even though the peaks of the two curves may be the same, thus giving you "equal" max. pressure, the shape of the curve may not be the same.

Particularly, the shorter the powder column, the quicker the rise of the pressure curve, due to improved powder ignition by the primer. Further, the better ignition would lead to more complete combustion of the charge, leading the pressure curve to remain higher after the peak. This increases the area under the curve, but not (necessarily) "peak pressure".

A do-able, practical test would be to take the 30-06, the 300 Win and the 300 WSM, fire each of them over a sheet, using the same bullet weight, collect the unburnt powder and weigh it. That would be one method of quantifying "efficiency" of the powder burn.

Fortunately, I don't have any of these chamberings, or I'd be out there satisfying my curiosity this weekend..........

I'm sure someone more knowledgeable will chime in with a better dissertation.

Some lower-pressure cartridges burn more powder at lower pressures, and produce higher velocities, than some high-pressure cartridges (smaller) produce at higher pressures.

To put ol' buddy Dutch's answer a bit differently, some light loads in a given cartridge can produce very high pressures but produce relatively less propelling gas and therefore lower velocities, while heavier charges of a slower powder produce significantly more propelling gas at lower peak pressures. The key lies in how high the average barrel pressure is, all the way from the case to the muzzle � not how high the pressure peak is.

Electronically recorded pressure curves, showing the pressure rise to the peak and the relatively abrupt or relatively more gradual "fade" to the muzzle in each case, show this relationship very graphically.

My files include curves that rise sharply to high, sharp peaks, but then fade fast to very low muzzle pressures (net low average pressures). Other curves on file show the pressures rising more slowly � to lower, longer, more-rounded peaks � and fade very little as the bullet approaches the muzzle. In the curves that I have in mind, the lighter charge of a faster powder produced a higher peak but a lower velocity. The heavier charge of a more suitable (slower) powder produced a lower peak and higher velocity.

The total volume of the propelling gas determines the velocity. The volume of gas comes directly from the volume of the powder. More powder converts into more gas, which accelerates the bullet faster in the barrel. Faster acceleration over a given distance (net barrel length) produces higher velocity at the end of that distance.

[This message has been edited by Ken Howell (edited 08-30-2001).]

Monitoring several reloading manuals, I found only Sierra giving data for both cartridges with the limitation that they used a test barrel of 23.5� for 6 PPC and for 6 x 47 a 29� barrel length. So, the absolute results (velocity and pressure) cannot be compared but only the relative development of speed and pressure:

6 PPC 25.3grs -> 2800 fps/1218ftlbs, 27.9grs -> 3100 fps/1493 ftlbs
6 x 47 24.5grs -> 2800 fps 28.7grs -> 3100 fps

What I can read out of these data is that 6 PPC needs 2.6 grains more of H322 to increase the speed by 300 fps whereas 6 x 47 needs 3.6 grains more. The same tendency with 748.

Taking into account the different barrel length, one may state that the difference is even bigger, but considering Ken�s last letter (volume behind the bullet), I am not so sure about that.

Hornady fifth edition, 65 gr. bullets:

H322: takes the 6x47 2.6 gr to gain 300 from 2900 to 3200 fps. Takes the PPC 3.1 gr. to go from 2500 to 2800 fps.

N135: the reverse ( 3.3 v.s. 3.0).

Why? I suspect that in this case, the "max" load was not established by strain gauge (a polite way of saying I think the book is wrong, I suppose). Dutch.

In the original post the statement was made that to compare the cases correctly the same barrel would have to be utilized for both cases. This is true. Furthermore, the same exact powder would have to be utilized. I do not mean the same type, but the exact same chemical composition (H380 for instance has a variation from batch to batch this is a production tolerance if you will) so as to generate the same burn characteristics. Then you would be able to determine what effect the case geometry had upon the burn rate of the powder.

This by the way is done with internal combustion engine design with regard to the combustion chamber shape in the cylinder head. Pressure transducers are utilized to measure tha actual cylinder head pressure generated during the combustion process. You need to be able to perform the same analysis here to get a meaningful analysis of the case design.

It can theorized that the short fat powder column reaches its maximum pressure sooner and remains near maximum pressure longer than the longer thinner powder column. To determine the mean effective pressure you would need to take the integral the pressure function with respect to time.

Anyway, unless someone has some expensive and specialized equipment we mere mortals will be left to ponder what is true and what is merely marketing BS.

Todd E

quote:

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Originally posted by Bruce Gordon:

Would a particular bullet (dia., style, weight, coating, etc.) driven at a particular chamber pressure give the same velocity in the same barrel?

The question sounds simple but I see some information that would indicate that the answer varies. The discussion about the relative merits of the short & fat powder column of the newer cartridge designs has me scratching my head and thinking that maybe there is something important I am missing.

---

YES! Same pressure will give the same velocity.

But, case shape may change the burn rate, hence changeing the pressure. This is the claim made by winchester for their WSM. Clearly, a different size case will change the pressure if the powder charge is not adjusted.

JerryO

Put a larger diameter case with the same bullet and powder charge (even if the case capacity is the same) the pressures will rise to dangerous levels in the larger case with IMR4895 but not the Unique - WHY? because the air space absorbs some of the pressure spike in the Unique load but there isn't as much in the 4895 load so pressures rise more quickly.

PaulS

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stay safe and live long!

To truly answer this question we are way past basic physics! The ideal gas law (basic physics)is PV=nRT. We are unfortunately not dealing with ideal gases. van der Waal's approximations may provide adequate data to make a fair comparison between two different case designs. Unfortunately, we do not have data to derive the values of a and b.

Also, we are not merely dealing with a gas, but with an additionally complex process of powder combustion. My approach was to use instrumentation and a controlled test mule to obtain data with which to base a conclusion. The try and proceed with an analytical solution you will need to write some custom software utilizing some complex physics. Furthermore, without the actual physical part analysis that I was talking about you have no way to validate your analytical (read mathematical model) method.

The actual physic being applied here is very similar to the combustion process in a spark ignition internal combustion engine. In this system (based on the Otto thermal cycle) we have an expanding gas which has been created by the ignition of an explosive mixture. The explosive mixture must not simply detonate (this would translate to excessive pressure in the cartridge) but burn at a uniform controlled rate. This provides a maximum push (maximum area under the pressure vs time curve)to the piston (bullet) and therefore maximizes engery conservation (efficiency).

I apologize for talking about engine combustion processes on this board. It is something I have some small knowledge with as I have spent 20 + years in high performance / racing engine development. It is just that this subject is such a good fit.

Todd E

Everyone who responded danced all around two important issues with out plainly stating that the short fat cartridge will always have a longer effective barrel lenth when compared to longer cases in the same length barrels, giving the short fat case an inherent velocity advantage. When you add in the efficiency of the longer barrel and the efficiencies of better load density ( I.E. less air space in the case), better ignition and powder burning chacteristics enherent in the short fat cases as compared with long skinny ones, the efficiency factor is considerable and cumulitive.

The reason short fat cases didn't generate much interest outside of bench rest and silhouette circles before is because they never had capacities large enough to develop velocities as good as their long skinny counter parts do. With the advent of the short mags, cartridges are now available to the general shooting public that develop enough velocity to generate considerable interest.

The short fat design's accuracy potential is well documented by how completely it has displaced all the older cartridge designs in the bench rest record books.

Because of the longer barrel length of the short fat case design and its girth, it is physically impossible to evaluate the two designs against one another in the same barrel. It would be possible to come very close by taking a thirty inch barrel and cutting it in half,converting each half into an Encore pistol barrel for each configuration in the same bullet diameter, utilizing the same reamers, brass, powder, primers and bullets,but it still wouldn't be the same barrel.

Frankly, I don't believe it's necessary to go to all that trouble because the reloading manuals on the market provide plenty of data for making these kinds of comparisons. We can compare the 221 Fire Ball to the 222 and 223 Rems, and then we can compare the 22 and 6mm PPCs and their Br counterparts to each other in both pistols and long guns; then we can compare the 7 Br in pistol s to the 708 in a pistol, and then compare the 708 in rifles to the 284 Win, 280 Rem and various 7mm mags in rifles, as well as all the other short and long configuration cartridges in all the other calibers offered.

What will we find after doing all this comparing? The short fat cases give more velocity for the amount of powder they burn than the bigger ones do and that more powder creates more velocity with a declining rate of efficiency , making small capacity cases more efficient than their larger counter parts irrespective of their configuration.

The new short magnums and a seried of wildcats developed by JD Jones, called Magnum Beaters - because they equal the rifle velocities of their '06 parents in 15" length encore pistol barrels, and do it with 10 to 15 grains less powder than the 300 class magnums require to reach the same velocities in the same length barrels, would appear to run counter to the widely held belief that more powder equals more velocity.

The reason that the short magnums develop equivalent velocities with less powder in light to medium bullet weights is because of their more efficient powder burning capabilities, longer relative barrel length and a powder capacity large enough to show what this case design is really capable of doing compared to the larger cases. I don't expect that the velocity will hold up in the heavier bullet weights because the requirements of the magazines in the short action rifles will require the heavy bullets to be seated deeply and impinge on available powder space.

The Magnum Beaters are a long skinny design that is beating equally long, or longer, and fatter case desings for a very different reasion: The limitations of back thrust. The smaller foot print ot the '06 case allows higher pressures to be run than 300 Mag and 404 Jeffery cases will allow in the Encore. The sharp shoulder (60 deg) and minimum body taper also reduce back thrust and leaves more metal in the barrel to with stand the the higher working pressures, also creating slightly more powder capacity than the parent cases have.

The magnum cases have more powder capacity than can be effectively burned in 15" barrels, contributing little or nothing to velocity or accuracy, adding only additional recoil, ejecta and noise. Conditions that are not conducive toaccurate or enjoyable shooting.

In closing I would like you to consider the lowly 22 Hornet, a mild cartridge that will drive a 50 Grain bullet at a modest 2418 feet per second with 9.5 gr of H 110 powder. Campare the Hornet with the awsome 30 - 378 Weatherby Magnum, driving a 150 gr bullet at 3498 feet per second. The Hornet averages 252.63 fps with every grain of powder it burns in this load, while the 30-378 averages only 34.29 fps for every grain of the 102.0 grains of IMR 7828 it takes to drice a bullet three times as heavy less than 1100 fps faster. The hornet is more than a hundred years old now. The 30-378 shows that we haven't made much progress in case efficiency during the last hundred years. In my humble opinion, the new short mags will be a big step in the right direction..Rusty.

Why are the short fat cartridges more efficient? That is the question that was asked. The only way to determine if the short and fat design is really more efficient is to measure the pressure generated during the combustion of the powder. The real question being asked is simply: Is the combustion efficiency better with the short and fat cartridge?

I agree with you regarding the shorter cartridges giving you more useable barrel length that is absolutely correct. You did not however demonstrate why the short and fat cartridge is more efficient. By the way, the 30-378 Weatherby Mag is somewhat over bore capacity. If you use a 30" - 32" barrel you will improve the velocity to powder burnt ratio. Besides comparing a 22 hornet to the 30-378 isn't fair there is a huge case capacity differential.

How about comparing the 22 hornet to the 22LR. I am not sure what the 22 LR load is, but it will propel a 36 grain slug to 1780 fps.

Todd E

Griff

[This message has been edited by Bruce Gordon (edited 09-10-2001).]

With reguard to pressure, the loading data put out by the powder manufacturers usually quotes pressures because that information is helpful in deciding which of their products to use in a certain application.

The load data put out by the bullet manufacturers usually ignores pressures because all loads given are within SAAMI specks. The pressure data powder mfgs put out can be missleading because it will change with bullet changes, and since they don't sell bullets, they use many different brans of bullets with only the powders they sell. Since the bullet people sell only bullets, they promote their products and use a lot of different powders, which provides more useful informmation for the average reloader.

Pressure is primarily used to establish safe standards and loading practises. It doesen't tell us very much about velocity or efficiency, but it can be very useful from the stand point of accuracy. However, the average shooter's ability to moniter pressure is limited.

There is more than one way to skin a cat and efficiency can be determined without any definitive knowledge of pressure. All we need to know is the powder charges and velocities being developed at given barrel lengths with the same bullet type and weight to determine efficiency.

Efficiency is getting the most return (velocity) for the least investment (powder burned). If we have two cases of differing configurations and the powder charges are equal and one develops substantially more velocity, the higher velocity case will be the more efficient case. If we have two cases of unequal capacity and they equally efficient, we can expect the velocity fall of to equal the powder differential in a perfect world. The trouble is,we don't live in a perfect world. Friction, and the forces it takes to overcome it, will always make the larger case less efficient.

If the smaller case is more efficient, and we already know that it will be, we will se that the velocity fall of will be less than the powder differential. Exanples:

221 Fireball:
Barrel: Lilja, 14", 1-12 twist.
Bullet: 40 gr Nbt.
Powder: RL 7 Max. 19.0 gr.*
Velocity: 2953 fps.
Load density 95 %
SAAMI: 52,000 cup

223 Remington:
Barrel: Lilja, 14", 1-12 twist.
Bullet: 40 gr Nbt.
Powder: RL 7 Max. 23.5 gr.*
Velocity: 3211 fps.
Load density: 83%
SAAMI: 52,000 cup

Results: The 221 holds 80.85% of the 223's powder charge, but develops 91.96% of its velocity.

If we compare the 7mm Br to the 7mm-08, the specs are as follows:

7mm Br:
Barrel: Lilja, 15", 1-9 twist.
Bullet: 140 gr Nbt.
Powder: IMR. 4895 30.0 gr.*
Velocity: 2248 fps.
Load density: 96%
SAAMI: 52,000 cup

7mm-08 Remington:
Barrel: Weisman, 14", 1-9 twist.
Bullet: 140 gr Nbt.
Powder: IMR. 4895 41.0 gr.*
Velocity: 2456 fps.
Load density: 84%
SAAMI: 52,000 cup

Results: The 7mm Br case gets 91,15% of the 7mm-08's velocity with only 73.71% of its powder.

So far all of these comparisons have been for handguns, lets look at the 7mm-08 and the 280 Remington in rifles.

7mm-08 Renington:
Barrel: Wiseman, 26", 1-9 twist.
Bullet: 140 gr. Nbt.
Powder: IMR. 4895 41.0 gr.*
Velocity: 2862 fps.
Load density: 84%
SAAMI: 52,000cup.

280 Remington:
Barrel: Lilja, 26", 1-9 twist.
Bullet: 140 gr. Nbt.
Powder: IMR. 4895 44 gr.*
Velocity: 2840 fps.
SAAMI: 60,000 psi.

Results: This is not the best powder for the 280, so lets look at both cases with IMR. 4350 before drawing any conclusions.

7mm-08 Rem.
Bullet: 140 gr. Nbt.
Powder: IMR. 4350 46.0 gr.*
Velocity: 2840 fps.
Load density: 94%
SAAMI: 52,000 cup.

280 Rem:
Bullet: 140 gr Nbt.
Powder: IMR. 4350 52.5 gr*
Velocity: 2940 fps.
Load density: 83%
SAAMI: 60,000 psi.

Results: The 7mm-08 gets 97.34% of the 280's velocity with 87.61% of its powder with 4350owder; with 4895 powder, the 7mm-08 exceeds the 280 in velocity by 22 fps.

For the final comparison we will look at the 7mm STW, in comparison to the mild mannored 7mm-08.

7mm-08 Rem
Barrel: 26" Wiseman, 1-9 twist.
Bullet: 140 gr. NBT.
Powder: RL 19 49.0 gr.
Velocity: 2922 fps.
Load density: 100%
SAAMI: 52,000 cup.

7mm STW
Barrel: 26" Lilja, 1-9 twist.
Bullet 140 gr Nbt.
Powder: RL 19 75.0 gr.
Velocity: 3362 fps.
Load density: 82%
SAAMI: 65,000 psi.

Results: As missmatched as this pairing is, the 7 mm-08 still develops 86.91% of the STW's velocity with 34.67% less powder. Now that's efficiency.

If we were to reverse this process and compare the 223 to the 22 Br, a long skinny case with less case capacity than a shorter fatter case, the results would be much the same because the short fat case has the disadvantage of a larger powder charge.

I stand corrected, short fat cases have better accuracy potential but not necessarily better velocity potential. Similar capacity cases will deliver similar velocities at similar pressures irreguardless of their configuration, just as smaller cases will always show an efficiency advantage in their velocity profile irreguardless of shape when compared with larger cases...Rusty.

Short, fat cases have only one real-world advantage: They fit in shorter actions. Any other advantage is nothing more than commercial hype. Since the shortfat cases are for brand new guns of known origin, the factories will load them to higher pressures, therfore factory velocities will exceed similar-capacity existing cartridges (at least for the next few years).

If you want more magazine capacity, use a .30-06 Improved loaded to 62,000 PSI in a Sako, Mauser, similar 5-round magazine action. If you want a short action and are willing to settle for only 2 or 3 rounds in the magazine, then get yourself a .300 WSM and shoot your choice of factory or hand loads. Velocity, accuracy potential, and deceased game will be, for all intents and purposes, the same.

There are several things that muddy the water and curdle the milk. Here are some of my observations and experiences.

The producers of short magnums use powders that you and I will never know and may never be able to purchase. Sometimes these are, or were in the past, a special blend ordered by the manufacturers. They want to ensure that reloaders won't duplicate the performance because they are in the business of selling loaded ammunition.

We apparently only have the word of the producers of short magnums that their cartridges are 10% more efficient or use less powder.

Powers not only come in many shapes and sizes, they also come in different compositions and with different performance characteristics. For example:

1. Single base and double base ( nitroglycerine impregnated ).
2. Flake, ball ( spherical ), stick ( like spaghetti ).
3. Deflagration or burn rates that vary. There are more than 100 different powders arranged in categories beginning with the fastest and ending with the slowest. Added to this, the characteristics of burning can be changed by coating the grains.

Different powders will burn in differenrt ways. Stick powder that is hollow will burn inside and out. As powder deflagrates its burn rate changes as surface is exposed. Bench rest shooters will sieve their powders and segregate the grain sizes to achieve more uniformity and consistency.

Some powder experts that I have talked to do not, themselves, fully understand what occurs inside the case and they cannot explain in detail the procedure.

Using exactly the same load, same case, same bullet, same rifle, same powder, same everything, there will be a variation in velocity from one shot to the next.

Using two of the systems of measuring pressures, CUP copper crusher and pressure transducer, some cartridges ( ranging from .22-250 to .45-70 government ) will register a higher CUP, some will register a higher transducer PSI ( pressure reading ) and some will be the same value CUP vs Transducer.

Interestingly, some of the cases that do not have a shoulder such as the .45-70 register CUP the same as PSI. The 30 carbine is another equal-equal. The 35 Remington CUP higher than PSI. The .22-250 has a CUP lower than a PSI pressure transducer reading while the 8mm Remington Magnum has the greatest difference. The Transducer reading is 11,000 psi higher than the CUP reading.

From these observations the conclusion can be drawn that the INTERNAL SHAPE of the case and THE BOTTLENECK have an influence on the speed and amount of pressure generated. It stands to reason that a larger opening that will allow gas to escape faster will pass the pressure through faster than a bottleneck which ( as the name implies ) will retard escape.

I know a gunsmith, who graduated from a gunsmith course in college, who has achieved about a 10% greater efficiency of a particular cartridge by doing nothing more that setting the shoulder ahead and changing its shape. He gets more velocity using less powder.

There is no single element that may contribute to the "advertised" success of short magnums. And there is no evidence available to the public for scrutiny that they are actually able to perform as advertised.

The impression that a "short magnum" performs better, of more efficient, or faster with less powder, may be just a magicians illusion. There is not enough information available to positively explain such a phenomenon, nor to prove or disprove it.

Kendall Dace