Best Cartridge Designs?

[dcali]

There must be more to it than short and fat. You can make a shorter fatter ppc sized case from br brass. But it did not take over the ppc for some reason.

My guess would be lower bolt thrust helps the PPC edge it out if you have the same capacity, but who knows.

 

[Forpest]

The best paper on barrel wear I am aware of was published in this book:

Amazon.com

Unfortunately, it's on the pricey side. But there's a survey of the literature in there that goes into a lot of depth.

My semi-founded in experience opinion is that Fred Zigler is more or less correct - that capacity is bar far the most significant contributor to velocity. You could think of extreme cases (like a long, pencil shaped case) where that gets distorted, but within practical limits, I doubt it matters. You can just look through a reloading manual and you'll see that. The SMc cases are really just an example of someone trying to eke out a tiny optimization. I think it's more interesting academically than practically, though.

When it comes to accuracy, I think it does matter *a little*. Thinner cases have less bolt thrust and that is what drives vibration. There are also pragmatic reasons to want one case shape over another (ease of sizing or case life for example). But I'm very much of the opinion that matching the capacity to the caliber, bullet weight, and barrel length is the most important factor in case design.

The SMc cartridges are much more than “eking out a tiny optimization”. If you compare any of those cartridges with a case of similar capacity, they will outperform it. The case design allows the use of slower burning powders, which further enhances their performance. I have shot - and chronographed over 3 chronographs simultaneously - a 5mm round out of the 5/35 SMc at more than 5200 fps! beats the .204 ruger my 200 fps with less powder. This line of cartridges did not take off because of the untimely death of By Smalley. By compared t the SMc cases with those of similar volume. He also designed at least 5 other wildcats as he experimented with his ideas. he designed the cases with straight shoulders, changed the shoulder angles, and then went to the radiused shoulder. The radiused shoulder improved efficiency, especially when slower powders were used. The slower powders allowed more velocity below peak pressure. I worked with him on a .22/32 SMc, and shot it in benchrest. The cartridge performed much better tha the shooter! He went on to develop a .22/40 SMc for varmint hunting. If I recall correctly, case capacity is a bit greater than ideal, but several things factor into that. First, you need a case to form the wildcat from, as it is a bit expensive to get a brass manufacturer to make brass to your specs! I have the reamers for the SMc cartridges if anyone wants to try them. I also have a 5mm/35, 22/32, 22/40, 6/55T (too fat - but again based on ease of forming brass from an existing case!), 6.5/65, and the only 30/100 in existence.

Zeglen’s take is not correct. The Savage custom shop chambered the 5/35, and Zeglin was given one. Smalley gave him brass and load info, but Zeglin knew better and did not use the slower burning powders that really make these cartridges shine Zeglin as not given one - it was Norm Johnson. Apologies to Fred and anyone else affected!

 

[Dave M.]

What level of barrel life are you getting?

My 6 dasher (rifle #3b) is currently at 4700 rounds and still putting up consistent scores of 595-600 at 600 yards.

 

[mike mccormick]

First, I don't know the answer. I'm speculating as much as you are. My suspicion is that the angle doesn't matter because within practical limits, the difference to the gas flow would be too small to measure. I'd buy it if the case was silly - like 1" diameter .17 caliber with a 60 degree shoulder. But 30 vs 40 degrees with a normal sized case head and caliber?

Think about barrel time - it's roughly .002 seconds give or take. That's the amount of time that the flame has to transfer heat to the bore. How much of a delay would the shoulder angle really make? I have a hard time believing it's enough to change barrel time significantly. Other things like barrel length, bullet weight and pressure would be more significant.

As I mentioned before there are some interesting papers on barrel erosion done by the military. Typically they measure barrel life in seconds, and have a pretty good understanding of the mechanisms. (mechanical wear, melting the bore, phase chance in the outer layer (the atoms reaarrange, slightly changing the volume occupied, which causes cracking), and a few other esoteric things.

Long story short, it's my belief that the primary drivers of barrel wear are charge weight, caliber, and barrel time. Charge weight is the total energy, barrel time is how long it has to seep into the bore, and caliber determines the amount of surface area that can soak up the heat (bigger calibers have a lower energy to surface area ratio).

For example, the 30 BR is known for having a long barrel life - big bore, light bullets, shorter barrel, and relatively small charge. A 6.5 x .284 is a known barrel burner - smaller diameter, higher charge, typically heavy bullets. Anecdotally, people seem to get better life out of .308s shooting 155 palma bullets than 200 grain F class bullets (because the heavy bullets increase barrel time).

But like I said before, this is all educated speculation.

I like the way you're thinking, but going by that logic, a 45-70 should eat barrels in no time at all. There is a lot more to it. Look at the known barrel eaters. A 223 wssm can cut the rifling out of a barrel in 200 rounds. Barrel time is extremely brief. I would say barrel time would be inversely proportional to wear rate. Double based powders erode barrels faster than single based, due to flame heat and duration. There are a lot of variables.

 

[VA_XTC_Shooter]

I did find one "mil" study, but it focuses on powders and temps and doesn't address case design.

https://apps.dtic.mil/sti/pdfs/ADA440938.pdf

 

[mauser284]

No such thing all cartridge designs are compromises.

Currently popular opinion is that you want a short fat powder colum with a sharp shoulder. Small primer pockets but hot primers and consistent primers!

I am not all in on modern cartridge design but I am not against it either.

Only less than brilliant people that believe in Santa Claus and the Tooth Fairy believe that all things equal a shorter reciever equals a stiffer reciever at the point of lock up and forward or that a short action in any way ineriently more accurate. This is especially true with locking lugs at the front of the bolt! If there was any truth in this rockets could never hit the moon let alone another rocket and tanks would never be able to hit another tank that are kilometers away with a smooth bore and rear interupted thread or a huge rolling block type action. Extreme long range precision shooting would all be dominated by short action super fat cartridges and it is not in fact how it works out!

So pick what application you are wanting to maximize for and pick a cartridge that has a history of producing the desired result. Once you fill comfortable with that cartridge and rifle setup then you can venture out from that. If it is fun it does not matter but if you want to win sometimes copying a winner and taking on a mentor that has a proven track record is the best way to go!

 

[dcali]

I like the way you're thinking, but going by that logic, a 45-70 should eat barrels in no time at all. There is a lot more to it. Look at the known barrel eaters. A 223 wssm can cut the rifling out of a barrel in 200 rounds. Barrel time is extremely brief. I would say barrel time would be inversely proportional to wear rate. Double based powders erode barrels faster than single based, due to flame heat and duration. There are a lot of variables.

By my logic, a .45-70 would eat barrels very slowly because the bore is huge (lots of surface area to absorb the heat). A .223 WSSM would wear them out very quickly because of the high charge weight and small bore. I would not be surprised at all to find that erosion is proportional to the ratio of charge weight to bore circumference. But yes, many variable that make it hard to pin down (and even harder to measure).

 

[Laurie]

By my logic, a .45-70 would eat barrels very slowly because the bore is huge (lots of surface area to absorb the heat). A .223 WSSM would wear them out very quickly because of the high charge weight and small bore.

Yes, with bells and whistles added!

Using the standard case capacity in grains water from QuickLOAD to bore area ratio method used in barrel life calculators and suchlike, you get 79gn divided by 0.165 sq inches = 478 for the 45-70.

223 WSSM's equivalents are 53.6 over 0.039 = 1,377

478 is a very low value indeed for this metric with very few designs as low as this. Equivalents are .30BR (527); .30-30WCF (587). You have to go to the really small cased cartridges like .22 Hornet to find anything with a lower value (372).

The 223WSSM's 1,377 falls within the loose definition of being 'over bore capacity' with the 7mm Rem Magnum (1,301) usually regarded as setting a boundary here.

THEN ..... on top of that, 223WSSM's SAAMI MAP is somewhere around 65,000 psi whilst 45-70's is 28,000 psi.

 

[Forpest]

This thread started with ideal shape cartridge shape for accuracy, but there are some other factors besides shape involved. The 6PPC dominates bench rest because it is accurate, but also because it has many quality bullets to choose from, and the cartridge allows the shooter to shoot free recoil for 50 + rounds a day without being shell shocked. Score shooters choose the “short” 30’s because there are quality bullets available. Those rifles can compete with PPC at short range for a few groups before recoil/shooter fatigue comes into play. Large bullet diameter comes into play. Light, quality .30 cal bullets are optimal size for scoring but offer manageable decay. .33 cal bullets would score better, but few quality bullets, and increased recoil. A bench rest quality .45 would be awesome, but no bullets and the recoil would kill. I know nothing about F-class, but I think it involves getting high BC bullets, minimally affected by wind, down range as fast as possible. Many of these requirements for the particular game drive the selection of the cartridge. Gotta love all the games to choose from. It’s just money, right?

 

[dcali]

Yes, with bells and whistles added!

Using the standard case capacity in grains water from QuickLOAD to bore area ratio method used in barrel life calculators and suchlike, you get 79gn divided by 0.165 sq inches = 478 for the 45-70.

223 WSSM's equivalents are 53.6 over 0.039 = 1,377

478 is a very low value indeed for this metric with very few designs as low as this. Equivalents are .30BR (527); .30-30WCF (587). You have to go to the really small cased cartridges like .22 Hornet to find anything with a lower value (372).

The 223WSSM's 1,377 falls within the loose definition of being 'over bore capacity' with the 7mm Rem Magnum (1,301) usually regarded as setting a boundary here.

THEN ..... on top of that, 223WSSM's SAAMI MAP is somewhere around 65,000 psi whilst 45-70's is 28,000 psi.

Thanks for doing the math! I feel like all those numbers make sense anecdotally. A list of those values would probably be of help to people concerned about barrel life. Maybe I'll sit down and make one some time.

 

[Laurie]

Thanks for doing the math! I feel like all those numbers make sense anecdotally. A list of those values would probably be of help to people concerned about barrel life. Maybe I'll sit down and make one some time.

I'm writing a feature on the subject right now for targetshooter.co.uk - up in a few weeks time. I got interested in the subject some time back, not so much for barrel life, more for powder burn-rates as (alongside bullet weight) this ratio is the main determinant of the powder needed. It works, but only up to a point as very small case cartridges (eg 6.5 Grendel) need faster powders than bigger numbers with a similar capacity to bore ratio, if nothing else to pack enough in to achieve full pressures.

As they used to print on children's toy boxes, playing around with these ratios 'guarantees endless hours of fun and amusement'.

Seriously though it's sometimes an eye-opener. I hadn't realised for instance just how much higher capacity .28 Nosler is compared to 7mm Remington Magnum, the latter long regarded as the yardstick for where 'over bore capacity' kicks in. Not that over bore capacity means that much anymore with so many super slow-burning powders added over the last 20 years.

 

[dcali]

I'm writing a feature on the subject right now for targetshooter.co.uk - up in a few weeks time. I got interested in the subject some time back, not so much for barrel life, more for powder burn-rates as (alongside bullet weight) this ratio is the main determinant of the powder needed. It works, but only up to a point as very small case cartridges (eg 6.5 Grendel) need faster powders than bigger numbers with a similar capacity to bore ratio, if nothing else to pack enough in to achieve full pressures.

As they used to print on children's toy boxes, playing around with these ratios 'guarantees endless hours of fun and amusement'.

Seriously though it's sometimes an eye-opener. I hadn't realised for instance just how much higher capacity .28 Nosler is compared to 7mm Remington Magnum, the latter long regarded as the yardstick for where 'over bore capacity' kicks in. Not that over bore capacity means that much anymore with so many super slow-burning powders added over the last 20 years.

Interesting stuff. Another fun thing to think about is that in theory (all else equal, which it never is), two cartridges with the same powder to bullet weight ratios will produce the same velocity.

 

[dcali]

Yes, with bells and whistles added!

Using the standard case capacity in grains water from QuickLOAD to bore area ratio method used in barrel life calculators and suchlike, you get 79gn divided by 0.165 sq inches = 478 for the 45-70.

223 WSSM's equivalents are 53.6 over 0.039 = 1,377

478 is a very low value indeed for this metric with very few designs as low as this. Equivalents are .30BR (527); .30-30WCF (587). You have to go to the really small cased cartridges like .22 Hornet to find anything with a lower value (372).

The 223WSSM's 1,377 falls within the loose definition of being 'over bore capacity' with the 7mm Rem Magnum (1,301) usually regarded as setting a boundary here.

THEN ..... on top of that, 223WSSM's SAAMI MAP is somewhere around 65,000 psi whilst 45-70's is 28,000 psi.

Just had another throught. I have a feeling volume to bore circumfrance might give a better indication, seeing as circumfrance is a direct measure of the surface area of the bore exposed to flame.

 

[Fuj]

Just had another throught. I have a feeling volume to bore circumfrance might give a better indication, seeing as circumfrance is a direct measure of the surface area of the bore exposed to flame.

I have wondered about the shape of the bottom of a given case.
Normally the internal case bottom is flat, then the primer, in mili-
seconds, blows powder forward as it ignites it. A shorter and wider
case could or would have a much shorter lag time in flame travel.
Gets me thinking about maybe a cases internal bottom might have
an advantage being funnel shaped ??.....Thinking out load......

 

[Forpest]

I have wondered about the shape of the bottom of a given case.
Normally the internal case bottom is flat, then the primer, in mili-
seconds, blows powder forward as it ignites it. A shorter and wider
case could or would have a much shorter lag time in flame travel.
Gets me thinking about maybe a cases internal bottom might have
an advantage being funnel shaped ??.....Thinking out load......

Read the SMc patent info linked earlier in this thread. It provides the best explanation I have seen about what happens after the primer strike. Primer particles/gases/flame blows thru and against the powder. The shoulders keep powder in the case, but once the bullet moves a plug of unburned powder follows the bullet down he bore. .

 

[davidjoe]

Interesting stuff. Another fun thing to think about is that in theory (all else equal, which it never is), two cartridges with the same powder to bullet weight ratios will produce the same velocity.

I think Hornady had that in mind with the PRC line. The 6.5, 7, and 300 PRC stair step up that way in cartridge capacity.

I have always considered the proportions of the bore to dictate the shape of the case. If covered earlier, apologies.

We all have these from which to verify, but our .45 ACP’s in 1911’s will have the most square or nearly “spherical” powder column of our firearms. The barrel is only about 10 calibers long and the powder must expend energy in a short distance.

We all also have 9’s. We have probably noticed that a 9mm and a .45 see exactly eye to eye, the .45 is simply fatter, meaning the 9 has a relatively more elongated powder column, and invariably a longer barrel in terms of number of calibers.

This trend line plotted on a graph should hold true of every gun we own. As the barrel lengthens in how many calibers long it is, the powder’s utility in pushing the bullet along the entire length of the barrel is maximized by the spreading out of its burn. It may be relatively benign illusion that something like a 6BR is better in a 33 inch barrel, than something like a .243.

A long column where burning powder pushes a plug of kernels into the bullet that only ignite as the bullet is much further down the barrel is in that sense, more efficient in terms of maximizing velocity than a column that expends its energy from primer ignition in the shortest period of time.

I have never been able to embrace steeply angled shoulders for the reason that they don’t direct that plug of moving powder into the neck (as well). In my mind, that power so situated is brought nearly to a dead stop, just as our reloading funnels would do to a powder charge we drop into a weakly angled funnel. The funnel, and the shoulder, are analogs.

It stands to reason that pressure generated in different areas of the case don’t necessarily all contribute equally to the forward motion of the bullet. Assume a right angled junction at the body and shoulder, kernels expanding in that “corner” region will actually be slowing down the momentum of any gas and powder attempting to enter the neck.

 

[Infrequent Shooter]

I think Hornady had that in mind with the PRC line. The 6.5, 7, and 300 PRC stair step up that way in cartridge capacity.

I have always considered the proportions of the bore to dictate the shape of the case. If covered earlier, apologies.

We all have these from which to verify, but our .45 ACP’s in 1911’s will have the most square or nearly “spherical” powder column of our firearms. The barrel is only about 10 calibers long and the powder must expend energy in a short distance.

We all also have 9’s. We have probably noticed that a 9mm and a .45 see exactly eye to eye, the .45 is simply fatter, meaning the 9 has a relatively more elongated powder column, and invariably a longer barrel in terms of number of calibers.

This trend line plotted on a graph should hold true of every gun we own. As the barrel lengthens in how many calibers long it is, the powder’s utility in pushing the bullet along the entire length of the barrel is maximized by the spreading out of its burn. It may be relatively benign illusion that something like a 6BR is better in a 33 inch barrel, than something like a .243.

A long column where burning powder pushes a plug of kernels into the bullet that only ignite as the bullet is much further down the barrel is in that sense, more efficient in terms of maximizing velocity than a column that expends its energy from primer ignition in the shortest period of time.

I have never been able to embrace steeply angled shoulders for the reason that they don’t direct that plug of moving powder into the neck (as well). In my mind, that power so situated is brought nearly to a dead stop, just as our reloading funnels would do to a powder charge we drop into a weakly angled funnel. The funnel, and the shoulder, are analogs.

It stands to reason that pressure generated in different areas of the case don’t necessarily all contribute equally to the forward motion of the bullet. Assume a right angled junction at the body and shoulder, kernels expanding in that “corner” region will actually be slowing down the momentum of any gas and powder attempting to enter the neck.

I think the 30 degree shoulder is a good solution, which is the original improved cartridge... I think. It took me a lot of reading to get that into my head. All I hear and read about is AI vs Improved.

 

[jackieschmidt]

There must be more to it than short and fat. You can make a shorter fatter ppc sized case from br brass. But it did not take over the ppc for some reason.

I knew several shooters who shot .125 shortened BR’s, and they were very accurate. Many used them because they were still using accurized REM actions with the .473 bolt face. Many of these were in Davidson sleeves.

The biggest drawback to the BR short is the PPC is so easy to make. You just turn the necks, (if needed), and fireform it.

With the BR, you have to push the shoulder back with an appropriate die, trim it back, turn the neck, then fireform it.

When it’s all said and done, I’m not real sure the shortened BR isn’t just as capable.

 

[Alex Wheeler]

I knew several shooters who shot .125 shortened BR’s, and they were very accurate. Many used them because they were still using accurized REM actions with the .473 bolt face. Many of these were in Davidson sleeves.

The biggest drawback to the BR short is the PPC is so easy to make. You just turn the necks, (if needed), and fireform it.

With the BR, you have to push the shoulder back with an appropriate die, trim it back, turn the neck, then fireform it.

When it’s all said and done, I’m not real sure the shortened BR isn’t just as capable.

It would hold primers a little better with more brass around them. I dont really think we are pushing the ppc any harder than the BRA based on brass life and pressure signs.

 

[VA_XTC_Shooter]

From Whelen's book, Vol, 2 - he indicates the shoulder angle plays a role in redirecting the "gases back on themselves, assuring faster and more complete burning of the powder. Apparently the pressure, although high, is more uniform, resulting in a flatter trajectory and better accuracy. A large proportion of this powder is consumed within the case, and no so much of it appears to burn in the and on the bullet seat, leade, and bore. As a consequence erosion proceeds more slowly and the accuracy life of the barrel is prolonged."

"A small arm is relatively inefficient form of gas engine. Ordinarily it utilizes only about forty to sixty percent of the gas generated in the useful work of propelling the projectile. The remainder is dissipated in developing heat, overcoming friction, expanding the case, in recoil, gas escape and otherwise. But the case with the abrupt shoulder seems to increase the proportionate effectiveness of the rifle."

Unlike my original statement about the angle directing gases to the neck wall vs barrel wall (really only seems to be possible in 40* or steeper angles with long necks. It is more, at least according to Whelen, about the more efficient combustion within the case.