What is the actual case capacity of a 378 WBY Magnum case? Water and whatever else they use to measure it. Thank you Gentlemen.

135.6 grs per Loadtech.
Jeff

Thanx!

That is very interesting. I have never owned a 378 Weatherby mag, but my 460 Weatherby magnum only had a case volume, in grains of water, of 134 - 136. With the 134 being resized and 136 being fired and not sized.



The 500 A Square has a measured volume, in grains of water, of 139 to 141. Norma cases necked up and fireformed.



The 416 Rigby is 126.5 - 127.5 depending if it is Norma (126.5) or Federal (127.5).



I therefore know that the 378 Weatherby doesn't have more than 134 grains of case capacity and should be considerably less.



If I had to make an educated guess, I would say that the 378 Weatherby magnum is close to a 416 Rigby. So I will say 127 gr with a max of 128.5.



Someone with a 378 please measure it and tell me how close my guess is.



Scott



Edits are in bold faced print. Sorry about switching the manufacturers around was posting from memory, which is often dangerous.

Scott....Obviously I have one....How do you get the measurement?

Prime an empty case. A spent primer is fine. Weigh it. Fill the case full of water. Weigh that. The difference is the water capacity. A drop of detergent in water helps both to "wet" the inside of the case and reduce the effect of the meniscus at the brim of the neck.

This is the question I have....Fill it to the top or tothe bottom of a seated bullet? SEE?

Load from a Disk says: "Full Case Capacity (grains water): Amount of water an empty case will hold." for 378 Wea mag is 132.88 grains.

It got even more inyeresting when I rung up the 460 Wtby. 145.5 grs??? I guess I won't trust the program that far. And maybe look at Quickload.

Jeff

Maybe they used heavy water?

Accuload's Calculoader has 139.8 gr of water for the capacity...

No wonder reloading is NOT an exact science!

It's 122 grs with a 270 Nosler Partition and 115 with a 300 seated to COL 3.690. Since there bullets displace 11 and 18 grs of water at that depth, respectively, total case capacity is about 133 grs.

The 378 Weatherby will become extinct once good rifles are chambered for the 375 RUM...it has the same power and trajectory at safe handloaded pressures with 14% less powder and fits a standard bolt face and mag action. Any 375 H&H chamber can be cleaed up to 375 RUM and fired with minor rail mods.

Referencing RCBS software,
To case mouth (H20) 338-378 378
w/ .020 wall taper 128.7gr 132.9gr
w/ .030 wall taper 124.0gr 128.2gr
w/ .040wall taper 119.5gr 123.7gr

Donnelly's "Cartridge Conversions" shows it as
134.74gr/ 8.73CC's 138.45gr/ 8.97CC's

Hope that is of some assistance, even though it confuses the issue somewhat.

I really find this interesting. First off, both CalcuLoader and LoadTech use data that is extracted from AccuLoad for maximum case length, capacity, OAL, etc., so naturally, they're all the same.
Secondly, I'm the guy that took that capacity reading. Now I'm not above "fat-fingering" a keyboard, so I pulled the reference case from the file and measured it again. I use modeling clay to seal the primer pocket, but that doesn't make any difference in capacity. The case I used was a 378 Weatherby case. Scale used was the RCBS Digital scale (the larger of the two they sell). I went through the entire zeroing procedure in their book and then came up with the following:
Empty weight (with clay) = 316.9 grains
Full to case mouth (still has clay) = 452.5
Difference = 135.6 grains
I repeated this test and took the average of three readings.
Even though we are near the Savannah River Plant, "Home of Plutonium", I didn't use heavy water. I used plain old distilled water, obtained by the gallon from Wal-mart and used a hypodermic syringe to insert the water (keeps the air pockets out).
Looking at my records, I still have the data on 1,013 actual measurments of case capacity from .14-.221 Walker to .600 Nitro Express. I also still have 95% of the cases measured labeled and set aside just for questions such as these. The ones I don't have were loaned to me by Charlie Benke, Mark Pinkston and Neal Benson. After taking the measurements on these cases, they were returned to their owners.
Regards,
HockeyPuck

Hockey Puck,

I suggest then that either your scale is off or mine is. Do you have either a Norma or Federal 416 Rigby case? If you do please measure it and tell us what you come up with.

Of course if my scale is off then that explains some of those velocities I get, since my scale is reading anywhere from ~7 to 12 grains low. The variation seems strange since all these cases are nothing but necked up or necked down versions of the same basic case, so I should be off the same for each case??? Those Weatherby (that would be a Norma case by the way) cases of yours are alot lighter than mine too. Is your reference case full length sized?

My 460 Weatherby case (Norma) weighed 348.9 gr empty with a spent primer, and 483.2 gr filled with tap water. These weights are an average of 5 cases.

My Federal 416 Rigby case weighed 341.2 gr empty with a spent primer, and 468.6 gr filled with tap water. These weights are an average of 5 cases.

I calibrated my scale just before making these measurements and then verified the calibration by measuring two sets of calibration weights. Calibration weights are 5, 10, 15, 20, 25, and 50 grams. The scale is calibrated with the 20 and 50 gram weights. The scale repeated within +/- 0.2 grains at each weight.

Scott

I just looked at Chuck Hawkes case capacity page http://www.chuckhawks.com/rifle_case_capacity.htm
and while he doesn't show the 378 Wtby,his numbers for the 460 are pretty close to what I came up with Loadtech,so I'll assume the 378 numbers are within reason also.
Ed,my apologies for jumping to conclusions.
Jeff

jsr,

The data on the website you provided appears to be a verbatim copy of the capacity data in the Barnes manual. Some of it I agree with some I do not. For instance I agree the 300 Win mag, R-P brass is around 90 grains. I agree with the 30-06 and the 308 as well. So does my scale! So praytell, why does my scale suddenly disagree with the 416 Rigby and 460 Weatherby by such a large margin.

POP, have you measured your cases yet? When you do please post your findings.

Scott

ScottS,
I only have the test/calibration weights that RCBS supplied with the scale, 20,50,70. The .378 Weatherby Magnum in my possession is headstamped Weatherby, so I assume its made by Norma. The case is new and obtained from Huntington's.
I do not have a .416 Weatherby, so the capacity in our programs was obtained from previously published data.
The .460 Weatherby in my possession is also headstamped Weatherby. It's unfired and was obtained as part of the Richard Simmons collection that we purchased.
Empty = 314.2 grains
Full = 459.7 grains
Capacity = 145.5 grains
I hope each of you have a safe and joyous holiday.
Merry Christmas!
Regards,
Ed

Hockeypuck,

Could you please measure your reference 416 Rigby case? Let me know the make of this case as well. I am truly concerned about my scale.

Thanks,
Scott

I just weighed a 460 case, Weatherby stamp. It is fire formed. It is also 2.903" in length (which is quite important here I might add), and capacity was 143.8gr flush to the top, no big bubble either. I use an eye dropper, and one drop is about .5gr FWIW. Oh ya, the case w/o water was 315.3gr, w/ water was 459.1gr...



I have a 416 WBY, so I'll go measure one too.

I also have 378 WBY and 338/378 WBY cases too.

if I remember right, the 338/378 was 131.5gr, or 133.5gr, but I'm not sure what the trimmed length was on it back then. More to follow...

416 Weatherby, Weatherby headstamp, fire formed:
2.904" length
461.8 gr w/ water
322.7 gr w/o water
139.1 gr water

378 Weatherby, Weatherby headstamp, fire formed:
2.902" length
437.2 gr w/ water
297.9 gr w/o water
139.3 gr water

Note: This case has been fired many times, not even sure how many, could be why it weighs more, but may have no effect... I've not measured the wall thickness at the pressure ring.

All the 338/378 Weatherby's are primed, so it ain't happening till they're fired.

Well, I think the data that has been provided here proves one very important factor... a reloader should sort his cartridge cases into lots based on something other than headstamp. Sorting by capacity would be one method, but it fails to take into consideration the strength of the alloy used by the individual manufacturer. Thus two cases of identical capacity, but different manufacturers, could easily produce two completely different sets of ballistic data.
The surest method is to purchase brass from a single lot and take a capacity measurement on perhaps 1 in 10. Average them out and use that as your capacity for that lot.
We have seen variations of around 5% of total capacity for the same cartridge taken by three or more individuals. I'm sure each of these measurements were taken carefully and reported truthfully. To me, they just indicate that capacity varies from manufacturer to manufacturer and even lot to lot. The only way you will ever know what YOUR case capacity is is to measure it yourself if you want greater accuracy than the 5% difference we have seen here.
Regards,
HockeyPuck

What does all this variation in case capacities really mean??

It means capacity varies somewhat from one lot of brass to the next, and also based upon the methods by which it is determined!

In addition, some seem to be talking about capacity to the base of theneck, or to the base of a bullet seated to a certain depth, or to the case mouth, all of which may or may not be trimmed to the same length, be unresized fired cases, or unfired new cases, or resized fired cases, etc.!!!