I've been reading about big 30s and 338s. I've seen load data on improved rounds that hold XX grains more powder than the original, but still use less powder than the original. Why? Does the improved shape make it more consistent? Longer case life? Both? Something else I'm missing?

the improved shoulder angles generally stop a case from growing.
it will also make a powder burn just a bit faster.
so a slightly lower powder amount is almost necessary since it's like switching burn rates.

are you talking 30/378 or light loaded 300hh?

the stated reasons why to improve a case are
1: changed case volume
2: longer case life (maybe!!)
3: better feeding or better/reduce bolt thrust (i don't really believe this one)
4: mechanical advantage of internal ballistics

#1 is real, I FIRMLY believe #4, in some cases, 2 and 3 are debatable

The 30/378 was one. IIRC, the 30/338 Lapua was another.

With load data I saw on the 30/338 Lapua, I think the 300 Tomahawk (300 RUM Improved) would offer the same performance for less money...but it's possible my memory is faulty here. But hey- the 1917 Enfield makes big boomers a little bit more affordable for us mere mortals.

DITTO ON Jeffe...

MOST shooters don't have the necessary equipment or ballistic expertise to measure all the required parameters...don't have the desire to muck about with testing and are only interested in certain aspects of their favorite pastime...NO FLAME OR DISS INTENDED...it's a fact of EVERY sport no matter what that sport is...some are interested in hunting and some in targets...and the factory ones have the economic angle imbedded in their product. Then you have the bullet construction problem, will the bullet "live" to get to the target.

Reloading data is infamously unreliable as you don't know all the particulars, some of it could be guestimates and only a chrono will tell.

The amount of increase in velo is only a percentage, roughly 2-2 1/2%, of the DIFFERENCE between the original case volume and the subsequent "improved" case volume.


AS the case volume increases and the powder amount increases, the velocity increase begins to fall off until the bore size reaches the "point of no return/velo increase", where you have to increase bore size if you want to increase velocity until THAT HITS THE WALL or there isn't a powder available that is useful.

And this little tome only covers a modicum of factors that influence actual useful gain in velo...I haven't mentioned the recoil factor at all.

Luck

Fun and games basically..

quote:

Originally posted by jeffeosso:
are you talking 30/378 or light loaded 300hh?

the stated reasons why to improve a case are
1: changed case volume
2: longer case life (maybe!!)
3: better feeding or better/reduce bolt thrust (i don't really believe this one)
4: mechanical advantage of internal ballistics

#1 is real, I FIRMLY believe #4, in some cases, 2 and 3 are debatable

Yes.
1 and 4....4 in Special.
Let burn the powder much better. Reduces Barrel Erosion.

Best
Wildcat

PS: 30/338 Lapua is one of the badest 30 Mags possible. Use a Shorter Case....

quote:

Originally posted by jeffeosso:
are you talking 30/378 or light loaded 300hh?

the stated reasons why to improve a case are
1: changed case volume
2: longer case life (maybe!!)
3: better feeding or better/reduce bolt thrust (i don't really believe this one)
4: mechanical advantage of internal ballistics

#1 is real, I FIRMLY believe #4, in some cases, 2 and 3 are debatable

RE: #2

My 8mm-06 A.I. cases seldom need trimming, don't show any signs of incipient case head separation and when "fauilure" ensues, it is due to enlarged primer pocket after a dozen or more reloads.

Now that I have switched to Norma MRP, I expect even longer case life due to lower chamber pressure over my previous IMR loads.

quote:

Originally posted by jeffeosso:
are you talking 30/378 or light loaded 300hh?

the stated reasons why to improve a case are
1: changed case volume
2: longer case life (maybe!!)
3: better feeding or better/reduce bolt thrust (i don't really believe this one)
4: mechanical advantage of internal ballistics

#1 is real, I FIRMLY believe #4, in some cases, 2 and 3 are debatable

There are other reasons people "improve" a cartridge. For example, sometimes a sharper shoulder angle is claimed to improve positive headspacing, and "improving" to increase case capacity will produce the same velocities as the unimproved cartridge but at lower pressures.

That said, probably the most prevalent reason for people to "improve" cartridges is to increase case capacity with the objective of achieving greater velocities. I owned Ackley's two-volume Handbook for Reloaders, read and reread them, gave them away, purchased another set several years later, read and reread those, and sold them off after a few years. Most of the improved cartridges only gained about 5% on their original case volume and velocity improvements were small unless filled with dubious loads that other experimenters later tested and reported as excessive. There are a few cartridges that benefit significantly from improving. Those tend to be very tapered cartridges and include the .300 H&H, .30-30, .25-35, and .250 Savage for example. Those were some of Ackley's favorites for his treatment.

Compare the .300 H&H with one of its improved iterations, the .300 Weatherby. The .300 Weatherby case holds 98.9 grains of water. That's a 15% improvement over the 85.9 grains of water volume of .300 H&H. But what does that mean? To put it into perspective consider that the .30-06 has 22% more case volume than the .308. So, yes, there is a greater case volume in the .300 Weatherby cartridge but it isn't really as big a difference as most people would think. Still, we know the .300 Weatherby can fire bullets much faster than the .300 H&H. How is that explained? Simple. A big part of the difference lies in the fact that the Weatherby is routinely loaded to higher pressures, one is a 58,000 psi SAAMI cartridge, the other a 65,000 psi SAAMI cartridge. If loaded to identical pressures the Weatherby would still best the .300 H&H but not by very much.

The comparison lends credence to the benefits of "improving" for reasons other than just an increase velocity. Jeffeosso is spot on.

The .30/378 and .30/338 Lapua are not "improved" cartridges. They are simply new cartridges created by necking down larger calibers much like the .22-250 and .25-06 are made by necking down the .250-3000 and .30-06 respectively.

Mans way is to tinker. Try something new or different.

quote:

Originally posted by LongDistanceOperator:
I've been reading about big 30s and 338s. I've seen load data on improved rounds that hold XX grains more powder than the original, but still use less powder than the original. Why? Does the improved shape make it more consistent? Longer case life? Both? Something else I'm missing?

Once in a North Carolina rifle shop, someone told me it was a waste of a 7 mm Magnum to download it.
I didn't argue the point, but 61 grains of 4831 with a 140-grain bullet has been plenty for 30-odd years now.