In order to participate in the GunBroker Member forums, you must be logged in with your GunBroker.com account. Click the sign-in button at the top right of the forums page to get connected.
Options
Optimal Shoulder Angles?
Alan Rushing
Member Posts: 9,002 ✭✭
What have the findings been the comparative effects regarding the 30 vs. 35 vs. 40 degree shoulder angles - with all else being equal?
My point of reference at present are the WSMs and the SAUMs though this influences many chamberings and ought be of interest others also. ((Another of my projects regards the 338 Ultra/RUM, but that is a bird of a different color.))
Some of the chamberings that come to mind, the gain would not be dramatic - as it had been in the past with the older shallow shoulder angles vs. the Improved.
However for some applications, such as in going head to head with simular chamberings - even gaining the space for several more grains might be significant, in some applications.
Would suspect that there ought to be a significant change in the efficiency of the powder burn and change in accuracy as well.
Perhaps comparing some of the short action 7mm chamberings would be in a matter of speaking comparing apples to apples. Been thinking some about the 284 vs. 7mm-08 vs. 7mm WSM vs. 7mm SAUM.
Knowledge, experience, information?
Where are we with this sort of research and information?
======================
Tailgunner1954 - I knew that I could count on you to give me something provocative to think about. I'll be mulling this over for at least a day or two to be sure. Appreciated . . . [;)]
======================
beantownshootah - (Forgive me for the tardy response, I've kept on these subject postings, on the Forum and off, but have been experiencing some significant internet provider and PC problems.)
I realize that I'd thrown these questions out in a generalized manner - My specific application was to utilize the sleeker silhoutte projectiles/gain a few more grains/bump the fps some/maintain or increase accuracy and the repeatability/efficiency of powder burn and grains per fps . . . Nothing new or unique I would imagine . . . but attempting to get the thinking and supposing done before the fact.
The specific critters that I am targeting at the moment are the 7mm WSM vs. the 7mm SAUM. Comparing the two, there are many things that I appreciate about each of them, there are also some things that do not appreciate about each individually.
=====================
sandwarrior - Ahhh a few more things to take in, thanks.
I realize that either original chambering as made is much more capable of accuracy and repeatability, than I am, ... I can wish, work, strive and even hope some. Who knows, maybe, just maybe the moon will be in the correct phase, the planets will align (in our system) and the stars up above will be pleased and generous. If I have the correct rig, at the correct place, etc., etc.
((I had done some study and figuring in the past re. them, but some family/life/death/multi-relocation stuff intervened with this and several other endeavors for a bit.))
============
I was looking for info that might descern what is gained and lost from 30 degrees to 35 and to 40 degrees or more. It would seem that therre might be one or more "sweet spots" on the shoulder angles for each chambering - butt hoping that spor might apply to a similar or related family of chamberings. I would suspect that there might be a relationship between say the 243 Win. and the 244 Rem and likewise between the similar "calibers" of the WSMs and the SAUMs, even though one might anticipate that their differing body tapers might well cause some differentian due to their body tapers varying from one another. Hoping that folks here and/or on the Handloading and Competition Forum might have some inkling on how far to go for the positives without getting into any negatives with the degree of shoulder angles.
With the longer length of the neck with the SAUM, compared to the 7mm WSM it seems it could be advantageous in seating and then throwing the higher BC rounds?
Believe that Winchester went in the right direction with their shoulder angles - taking them to 35 degrees! Did they go the optimal distance though? IF yes or IF no - how so? [?]
Why did Rem stop at 30 degrees and Win stop at 35 and NOT go further?
Why the heck did they not go to a straight walled body? Win's body taper harkens back at least to the 243 if not earlier!
My point of reference at present are the WSMs and the SAUMs though this influences many chamberings and ought be of interest others also. ((Another of my projects regards the 338 Ultra/RUM, but that is a bird of a different color.))
Some of the chamberings that come to mind, the gain would not be dramatic - as it had been in the past with the older shallow shoulder angles vs. the Improved.
However for some applications, such as in going head to head with simular chamberings - even gaining the space for several more grains might be significant, in some applications.
Would suspect that there ought to be a significant change in the efficiency of the powder burn and change in accuracy as well.
Perhaps comparing some of the short action 7mm chamberings would be in a matter of speaking comparing apples to apples. Been thinking some about the 284 vs. 7mm-08 vs. 7mm WSM vs. 7mm SAUM.
Knowledge, experience, information?
Where are we with this sort of research and information?
======================
Tailgunner1954 - I knew that I could count on you to give me something provocative to think about. I'll be mulling this over for at least a day or two to be sure. Appreciated . . . [;)]
======================
beantownshootah - (Forgive me for the tardy response, I've kept on these subject postings, on the Forum and off, but have been experiencing some significant internet provider and PC problems.)
I realize that I'd thrown these questions out in a generalized manner - My specific application was to utilize the sleeker silhoutte projectiles/gain a few more grains/bump the fps some/maintain or increase accuracy and the repeatability/efficiency of powder burn and grains per fps . . . Nothing new or unique I would imagine . . . but attempting to get the thinking and supposing done before the fact.
The specific critters that I am targeting at the moment are the 7mm WSM vs. the 7mm SAUM. Comparing the two, there are many things that I appreciate about each of them, there are also some things that do not appreciate about each individually.
=====================
sandwarrior - Ahhh a few more things to take in, thanks.
I realize that either original chambering as made is much more capable of accuracy and repeatability, than I am, ... I can wish, work, strive and even hope some. Who knows, maybe, just maybe the moon will be in the correct phase, the planets will align (in our system) and the stars up above will be pleased and generous. If I have the correct rig, at the correct place, etc., etc.
((I had done some study and figuring in the past re. them, but some family/life/death/multi-relocation stuff intervened with this and several other endeavors for a bit.))
============
I was looking for info that might descern what is gained and lost from 30 degrees to 35 and to 40 degrees or more. It would seem that therre might be one or more "sweet spots" on the shoulder angles for each chambering - butt hoping that spor might apply to a similar or related family of chamberings. I would suspect that there might be a relationship between say the 243 Win. and the 244 Rem and likewise between the similar "calibers" of the WSMs and the SAUMs, even though one might anticipate that their differing body tapers might well cause some differentian due to their body tapers varying from one another. Hoping that folks here and/or on the Handloading and Competition Forum might have some inkling on how far to go for the positives without getting into any negatives with the degree of shoulder angles.
With the longer length of the neck with the SAUM, compared to the 7mm WSM it seems it could be advantageous in seating and then throwing the higher BC rounds?
Believe that Winchester went in the right direction with their shoulder angles - taking them to 35 degrees! Did they go the optimal distance though? IF yes or IF no - how so? [?]
Why did Rem stop at 30 degrees and Win stop at 35 and NOT go further?
Why the heck did they not go to a straight walled body? Win's body taper harkens back at least to the 243 if not earlier!
Comments
Shoulder angle makes no difference. What matters is the total volume of the case. IOW cubic inch's rule
Barnes (gun writer)and Stitt? (gunsmith) did a experiment with the 300 WSM and H&H cases. Both cases have the same capacity, but radically different shoulder angles as well as the short/fat VS tall/skinny powder column thing.
They first chambered for the H&H and ran a series of powder charge/velocity. Than than cut off the breach end and rechambered with a WSM reamer that had everything forward of the case mouth removed (IE they insured that the throat and leede remained the same, as well as the effective barrel length) than repeated the charge/velocity run.
The result was that BOTH produced the same velocity with the same charge.
PO Ackley did a similar thing "back in the day", trying to prove that a tall skinny powder column was better than a "normal" one. He saw no "improvement" either. The Ackley case is the one on the left, modified 300 H&H, in the photo
ETA
quote:Originally posted by nononsense
Alan Rushing,
There is a venturi effect, if one reduces the diameter of a pipe or nozzle and likewise when one necks down a cartridge case........
With trigonometric relationships, we can solve where the point of convergence is, given the angle of the shoulder of the case. I will use the 6 mm PPC as an example. The convergence point will be on the centre line of the case neck or bore, so we can divide the diameter by 2 to derive the radius or the one side of a right triangle (A) that is formed. Since the angle of attack is 30 degrees, the other angle must be 60 degrees as the sum of the inside angles of a triangle must be equal to 180 degrees. The inverse of Tan is equal to Cot and vice versa. You can either use Cot 30* or Tan 60* as they can be proven to be equal.
A = (.243/2) = 0.1215"
B = a (cot A) = (0.1215 x 1.732) = 0.2104"
(P/L) = (0.2104/0.301) x 100/1 = 69.9%
This means that convergence takes place at 69.9% or 30.1% below the mouth of the case, leaving sufficient length to stabilise the collision or venturi-effect. Short necks also cause more throat erosion than those cartridges with longer necks. Let us do a comparison now to see if there is a positive trend or at least a degree of correlation.
Well, that math works out for LAMINAR flow, to bad we are dealing with the initial TURBULENT flow problem.
In the 2-4 Milli-seconds (there is only 5-6 ms between primer ignition and the bullet leaving the muzzle) that the majority of the powder gas is transiting the shoulder/neck of the case, it does NOT have time to go laminar.
Alan
IIRC you work in a higher education environment, perhaps you can take the above arguments to the head of the physics dept, and get his opinion (please let us know what he says)
Shoulder angle as a means to increase case capacity is logical. As case capacity is increased, powder burning rates need to decreased.
Both cases have the same capacity, but radically different shoulder angles as well as the short/fat VS tall/skinny powder column thing.
PO Ackley did a similar thing "back in the day", trying to prove that a tall skinny powder column was better than a "normal" one. He saw no "improvement" either.
If the question is purely about VELOCITY, then I think the relevant factor, as mentioned, is just powder charge. For that, the case volume is what matters, not its shape.
Case shape can matter for a whole bunch of OTHER (ie non-ballistic) reasons, though, like ease of extraction, ease of shaping/sizing the brass, brass wear patterns, etc.
Off the topic of shoulder angles, one real difference between tall/skinny vs fat/short cartridges is that fat-short cartridges can be run through guns with shorter actions. In other words, the overall case length affects the design of the gun in question.
Shorter action means less distance of bolt throw for a manual repeater, and/or less reciprocating back and forth motion for a semi (or full) auto gun, in both cases potentially leading to faster cycling times. Short action vs long action also potentially affects which stock model rifles a given round can be chambered into.
Also, magazine capacity is usually limited by case diameter, with the thinner cartridges offering the advantage here. All else being equal, you're probably going to be able to cram more thin long rounds into your gun's magazine than short fat ones.
Whether or not these things "matter" depends on your application. If you're slow-shooting targets for pure accuracy, capacity and action length probably don't matter much at all. If you're shooting at someone who is shooting back at you. . .they may matter a LOT more!
As another consideration, a really long powder "column" from a long and skinny cartridge can reduce the efficiency/consistency of primer ignition. Basically, if you have a long dense powder column, the fire from the primer strike might not evenly ignite all the powder in the case at once. Again, how significant this effect is in the "real world" depends on the cartridge geometry, primer type, powder density, and other factors, but this is something else worth thinking about.
I don't think I posted this before but Chris told me to have at it...
Take your time and let it sink in, the math isn't difficult. I am not advocating for this theory or the support of it, I'm simply passing it along for your edification. I have my own ideas but I'm not feeling augmentative.
Best.
Is there magic in a case's shoulder angle relative to its neck length?
By: C. Bekker
The 22 PPC cartridge was designed by Dr. Louis Palmasano and Ferris Pindell in 1974. The intention being to design an efficient benchrest cartridge. It was based on the 220 Russian case, which has a smaller head size than the 308 with a small rifle primer, a 30-degree shoulder and necked down to .224 calibre. The fact that the 22 PPC cartridge is winning benchrest matches support the theory of efficient case design, which is depicted here: -
The 6mm PPC is an outgrowth of the 22 PPC and has the same case configuration with the neck expanded to take 6 mm (.243") bullets. Body taper is minimal to ensure a firm grip in the chamber. The neck is slightly longer, .301" instead of .270", but it has the same shoulder angle of 30 degrees. The 6 mm PPC was also developed by Dr. Louis Palmisano and Ferris Pindell and is enjoying an even greater success than the 22 PPC.
This leads to the question if there is not perhaps a magic ratio between the shoulder angle and the length of the case neck. Both cartridges have the same case length of 1.515" which is considered "short". It is a known fact that shorter and fatter cases yield more velocity for the same amount of powder in relation to longer cases, but the fact that they are consistently winning competitions, seems to suggest that an ideal position or 'sweetspot' has been hit. So, let us focus on case dimensions and compare a few popular cartridges by using trigonometric calculations, and see if we can establish a meaningful trend.
There is a venturi effect, if one reduces the diameter of a pipe or nozzle and likewise when one necks down a cartridge case. The powder granules will collide and converge at some point, which can still be inside the neck or just outside depending on the shoulder angle of the case. I want to focus at this point of convergence to see what percentage of the neck is ahead of this point which apparently produce a more even pressure from then on onto the bullet. A 30-degree shoulder angle seems to create less turbulence than say a 40-degree angle, as the deflection of powder granules/gases off the neck wall is less and the collision in the centre of the neck is at a lesser angle. Thus it consumes less energy trying to get down the barrel. But what is wrong with a 20-degree angle that produces less turbulence? The only way I can rationalise this is, that the bullet swells at the base as it is pushed into the rifling of the barrel, and the 30 degree angle or thereabouts, seems to provide a more stable push from all sides to eliminate a yaw before entering, as opposed to a less sharp angle or no angle at all, where there is a greater change to gyrate as the tip of the bullet attempts to enter the rifling which also lies at an angle. I assume therefore that the pushing effect is more even, provided the convergence happens inside the length of the neck at some specific point. So, the ratio of the shoulder angle to the neck's length, will determine the point of convergence, which may be an important parameter in obtaining a sweetspot.
With trigonometric relationships, we can solve where the point of convergence is, given the angle of the shoulder of the case. I will use the 6 mm PPC as an example. The convergence point will be on the centre line of the case neck or bore, so we can divide the diameter by 2 to derive the radius or the one side of a right triangle (A) that is formed. Since the angle of attack is 30 degrees, the other angle must be 60 degrees as the sum of the inside angles of a triangle must be equal to 180 degrees. The inverse of Tan is equal to Cot and vice versa. You can either use Cot 30* or Tan 60* as they can be proven to be equal.
A = (.243/2) = 0.1215"
B = a (cot A) = (0.1215 x 1.732) = 0.2104"
(P/L) = (0.2104/0.301) x 100/1 = 69.9%
This means that convergence takes place at 69.9% or 30.1% below the mouth of the case, leaving sufficient length to stabilise the collision or venturi-effect. Short necks also cause more throat erosion than those cartridges with longer necks. Let us do a comparison now to see if there is a positive trend or at least a degree of correlation.
Cartridge NeckDiameterin inches R = RadiusD/2in inches ShoulderAngleDegrees L = lengthOf Neckin inches T = Tangent R x TP = Point ofConvergence PercentageP/L
222 Remington 0.224 0.1120 23 0.313 67 degrees = 2.3558 .2638 84.3%
223 Remington 0.224 0.1120 23 0.203 67 degrees = 2.3558 .2638 130.0%
22 PPC 0.224 0.1120 30 0.270 60 degrees = 1.7320 .1940 71.6%
6 mm PPC 0.243 0.1215 30 0.301 60 degrees = 1.7320 .2104 69.9%
6.5 x 55 mm 0.263 0.1315 25 0.320 65 degrees = 2.1445 .2820 88.1%
6.5-284 Norma 0.263 0.1315 35 0.270 55 degrees = 1.4281 .1878 69.6%
308 Winchester 0.308 0.1540 20 0.304 70 degrees = 2.7474 .4231 139.2%
30-06 Spr 0.308 0.1540 17* 16' 0.383 73.73 degrees = 3.2172 .4954 129.4%
300 Win Mag 0.308 0.1540 25 0.264 65 degrees = 2.1445 .3303 125.1%
In some cases the theory seems to gel, but in other cases it does not provide an explanation, for example:
1. There is general consensus that a 223 Rem cannot compete with a 222 Rem. The above table suggests a marked difference, but accuracy differences are not that big in reality. (84.3% vs 130%)
2. The 22 PPC takes a close second to the 6 mm PPC. The above statistics are indeed very similar and one tends to think that the dimensions do in fact play a strong role. (71.6% vs 69.9%)
3. None of the bigger calibres can compare with the 6 mm PPC out to 300 yards, not even the 6.5-.284 Norma and yet there convergence percentages are almost the same - 69.9% vs 69.6%. Perhaps its sharper shoulder of 35 degrees versus 30 degrees and its longer powder column come into play?
4. I expected the 308 Win to follow the theory more closely as opposed to the 30-06 Spr and 300 Win Mag. The 308 Win, with its shorter powder column and lower recoil, is generally superior over the other two longer and more powerful cartridges, contrary to what the above table suggests - a serious dichotomy! In fact, the 308 Win seems to be the worst of the bunch in terms of the theory - 139.2% which is 39.2% beyond the neck of the case and into the throat.
Here are some aspects that may vary from one rifle set-up to another:
? Capacity and shape of the case, relative to the chamber and throat dimensions, which will result in a specific operating pressure - different for each cartridge and its bullet/load combinations.
? The relative burning rate of the powder which also differ for each cartridge.
? The amount of powder used and the percentage 'case fill' - being inter-active with the above.
? The diameter, weight, and the bearing length of the bullet yielding different resistance.
? Length and interior dimensions of the barrel which refers to precision tolerances, twist rate and its consistency, number and depth of grooves, smoothness of barrel, a square crown and consistent barrel harmonics (i.e. stress-relieved or not).
? Uniformity of primer ignition and intensity relative to the loading density of the powder. If a primer is too hot for a given powder load, it will ignite the powder too fast, which will cause the pressure curve's front end to be steeper. Steep enough to slam the bullet into the rifling too hard. Probably hard enough to significantly upset (deform) the bullet's back end that it won't shoot so accurate.
So, it is not quite so simple to explain, as cartridges do have different lengths, different capacities and they all yield different pressure levels, which contributes to the efficiency of the burning, whereas the shoulder angle has to do with convergence and the neck length to absorb the collision of hundreds of particles. Furthermore, the above need to be brought in line with different throat dimensions that will affect the chamber pressure as well, as it too forms part of the overall combustion volume. Each cartridge uses its own propellant to work optimally and there is no magic formula for that. As burning rates differ, we know that some propellants work better than others in a given cartridge, and in some cases Somchem does not have the equivalent propellant of overseas manufacturers. In Rifle Accuracy Facts by Harold Vaughn, he stated the effects of bullet "cant" and verified that 'how the bullet enters the rifling' has a very dramatic and predictable effect on accuracy. He also discusses throat diameter and alignment with the bore and states that nearly every factory chamber he has studied was deficient in this regard.
So, many factors seem to be at work and it seems the jury is still out on explaining exactly the accuracy phenomenon of the 6 mm PPC, rather than solely case design and dimensions. We need a universal truth across a range of cartridges, before we can say the theory works.
30-06 Spr, 30-06 Imp & 7.82 (.308) Lazzeroni
Lazzeroni is confident though, that a shorter and wider case is the way in the right direction, as bolt flex is less in shorter actions in more powerful cartridges. Lazzeroni's cases are even fatter than the WSM's with the result that it is not easily adapted to a lot of bolt actions. The real test would be to mimic the dimensions of the 6 mm PPC in other cartridges and see if accuracy improvements will follow. For example, to redesign the 308 Winchester with a 30 degree shoulder and a 69.9 % convergence point in the case's neck, but never can the powder column be as short. Even if it cannot be mimicked, we do know that the 6 mm PPC design has hit a sweetspot. Perhaps the main reason is purely that it has a shorter and wider powder column in relation to its height, so that more powder is instantly ignited by the primer flame for a given depth, which presumably creates a more uniform burning of powder for a smoother pressure curve, which yields a smaller shot to shot variation.
Chris Bekker
In my journey through the history of various cartridges, a few stand out quite readily. The first is the .300 Savage. Quite an effective round that when loaded to comparable specs, come very close in performance to it's offspring, the 7.62x51/308 Win. The specific reason the shoulder was changed was for feeding. Otherwise, the 30 degree shoulder would have been kept. The reason for the neck being lengthened was to get more hold on the bullet. The .300 Savage gave all the performance the Army wanted. It just lacked in functionality for their purposes.
The second is the 6mmBR. As nn has pointed out in several posts from the past, this little cartridge is nailing down all the records it can handle. While 40 degree variances of the case are doing well also, I find I'm having trouble dealing with the 40 deg. shoulder in it's bigger cousin being way too finicky as I bring it up to that last accuracy node. Sit just a little too long in a hot barrel and my .1~something group is destroyed as I blow a primer on the last of five rounds.
Third is the 6.5 Grendel. When the bugs are worked out of each individual system, the accuracy capability is phenomenal to say the least. Three shots from an AR @ 1000 yds. at a 4 moa gong within 5 seconds. Repeated by two other fellow shooters immediately after me. All hitting center mass.
Another situation is the WSM/WSSM cases. Winchester did a study to find which really was the 'optimal' shoulder angle. For the WSM's the shoulder remained at 35 deg. for all caliber variants. For the WSSM's the cases of the .223 and .243 were 28 deg. while the 25 WSSM was 30 deg.
It has always been something I keep my eye on to see how it works with cartridges and shoulder angles in comparison with body width and bore area. I think as length of the cartridge increases shoulder angle has less of a bearing on the outcome as it does with shorter, "efficient" cartridges. I also know that as bore area increases the shoulder angle can be increased to enhance efficiency. An example there is the 9.3x62 which has a steep angle on it's shoulder which helps ignite the powder. However, not to the point it will cause an overpressure. Just that it helps medium speed powders ignite completely.