The Weatherby rounded shoulder

[TexWeatherby]

I'm not an engineer, but although ignition happens in a small fraction of a second, I think it may be possible or likely that there would be less turbulence in the gasses coming out of the neck if there are rounded corners to facilitate smooth gas flow instead of sharp corners for this to occur. Not entirely unlike air flowing around a vehicle in a wind tunnel - sharp corners, especially inside corners, cause turbulence. Just a thought.

[grizzly340]

I know that I read that the real reason was just to be diffrent. Probably in his book. I checked the index and didnt see it listed. But I will find it.
I remember doing side by side test with the same amount of sand. To see witch would empty faster. But I couldnt tell any diffrence.

[dubyam]

Maybe you or someone else on this forum can explain why an ackly improved cartridge reaches a higher level of performance than its original one with standard degree on the shoulder. I have to disagree with you that the shoulder angle has little to no bearing on a cartridges performance.  ctw   

There are two reasons Ackley Improved cartridges (or any Improved cartridge design, as many others "improved" cartridges but Ackley is the most famous) are faster than their unimproved parent cartridges. In my opinion, the primary reason is usually pressure levels. The secondary reason is the case volume is made larger by reducing the body taper and moving the shoulder forward. As for the primary reason, that's been a topic of debate for years, with folks denoting that pressure signs don't show up in the Ackleys until velocities are much higher than their parent cartridges, indicating huge gains without pressure issues. But this is a false equivalency, because the reduced body taper (straighter case walls) and steep shoulder cause the pressures to be exerted more in a radial fashion (outward into the side walls of the chamber) than a linear fashion (rearward as thrust against the bolt face), so the real pressures are marked, and typical Ackley velocities from PO's work and from other sources not testing things with pressure reading equipment, push those Ackley rounds up around 70-75kpsi, where the parent rounds are running 60-65kpsi, generally, and sometimes less. Consider the old argument that the 280 Ackley Improved is "all but equal to the 7mmRemMag." For that to be true, the Ackley (case capacity of 64.8gr of water, as per Nosler) would have to run significantly higher pressures than the 7mmRemMag (case capacity of 78gr as per Nosler) to achieve the same velocities. And in Nosler's pressure tested data, the Ackley indeed runs ~150fps slower than the RemMag, because case volume and pressure are the two key ingredients in developing velocity, if barrel length is kept even. Adding in the 280Rem (case capacity 62.5gr) with velocity about 80fps below the Ackley, and you see where the real key is - case volume. Even more impressive in this comparison is that the 280Rem and 280AI were both tested in 26" barrels, while the 7mmRemMag data was developed in a 24" barrel, giving even more edge to the 7mmRemMag's additional case volume.

[wyominghunter]

I agree with the write-up above. I have a few Ackley Improved cartridges (.22-250, .25-06, and .280).

Not much magic actually. They get some case volume gain by the process. I don’t push mine that hard, so I can’t quantify pressure. You don’t get as much stretching of the case and don’t have to trim as often. The Ackley Improved cartridges get close, but cannot match or exceed the related magnum case peers. Case capacity still is the dominant factor.

[zonie]

I have to agree with Duby and Wyoming hunter.  Case capacity, free bore and how efficient primers ignite powders, and of course the powders themselves and how they  burn given a specific barrel  length and bore size.    Years ago I read someplace old Elmer Keith was trying to develop a tube placed inside a cartridge case that was attached to the primer pocket which in theory would allow the primer flame to travel up inside this tube to the center of the case some distance before the actual primer flame would come in contact with the powder itself, thus causing the flame to spread out from the center of the powder column.    Even today I kind of thought it was kind of a weird idea and it never panned out I guess.  Freebore  is a way to increase powder  capacity while still maintaining optimal pressures increasing velocity,  I read that some where and seems kind of logical to me.   You want to get higher velocities try different primers they are not exactly the same power level, nor are they  interchangeable  without re-working up safe loads.  Getting cherry's and reamers made can be expensive as you want to make R & D originals  and a lot more involved than just designing one on paper.   I guess if all powders and bores were the same then I suspect a straight walled case would be the most efficient,  whether double radius shoulders cause something or other to happen to increase velocities by any significant amount my guess just  me just thinking out loud then why are current Wby powders blended and not available to the public or why have powders changed from birth to current powders ?  My guess it has to do more with freebore , powder capacities matched to bore sizes & bullet weights, differences in primers rather than a radius shoulder, but I could be wrong