Coindicence or by design?

Started by Paul Hoskins, January 11, 2019, 04:54:07 AM

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Paul Hoskins

A few days ago I was thinking about the 500 S&W Mag. & the 460 S&W Mag. A dangerous thing any more, thinking. Anyway I looked at the dimensions of the two cartridge cases & decided they must have about the  same case capacity. After some rough ciphering it turns out case capacity is almost identical. The .500 is 1.625" long with a diameter of .500" inside. The .460 is 1.800" long with an inside diameter of .452 inches. By multiplying the overall length & inside diameter of each one , I get the same answer. If the head thickness is the same on each case then the capacity is the same for the two cartridges. Necked to any other caliber I suspect one case is just as good as the other for a wildcat cartridge. The .460 would eliminate one step in necking down to a smaller caliber. .......Paul H

gitano

According to QuickLOAD, the nominal case capacities of the two cartridges are 60.0 and 63.5 grains of water for the .460 and the .500, respectively. (QuickLOAD specs are "factory" numbers. I have some .500 S&W cases I can measure.) That 3.5 grain increase for the .500 represents a 5.83% ((3.5/60.0)*100) 'advantage' in case capacity for the .500.

I wouldn't think that the ~6% increase in case capacity would matter TOO much for calibers smaller than .284. For calibers .284 and larger, I would think one would want to get get every bit of 'help' one could in terms of charge. So if I were necking down to .257 say, I would use the .460 case. Were I necking to 8mm, I'd want to use the .500 case. Of course that would be somewhat dependent on the weight of the bullet, not just the caliber. What I'm thinking of here is the .338x.308 Win (AKA .338 Federal and Marlin) in which the heavier bullets 'challenge' the case capacity of the .308 Win.

Considering your interest in "small" calibers, Paul, I would guess that the .460 would indeed be the more 'user-friendly' choice of the two. Are you making something?

Paul
Be nicer than necessary.

Paul Hoskins

Paul, good to see you're back among us. Hope you had a good time visiting the kids. ......I'm not particularly planning on making anything from the .500 or .460 S&W cases but a few years ago I was seriously considering the .500 for a stubby 6.5 cartridge in the Peabody Enfield I've been piddling with for several years. Still haven't worked on it any more in a few years but this summer I intend to finish it one way or another & chamber it for the 6.5-30 AI. If I'm not happy with the velocity I want I can always go with the 6.5-243 AI in a slightly modified form or the 6.5-257 Roberts AI. The barrel is only 22 inches  long though. :huh2: .......I have around 50 cases  necked to 6.5 from .500 S&W cases. Best I remember they hold around 50 grains of water. Just too much trouble to draw them to 6.5 caliber. .......Paul H

Paul Hoskins

Paul, I went back over my ciphering for the "volume" of the two cases in question & can't figure out how the factory or Quickload can find any difference in case capacity for the two cases. Assuming the inside case diameters are straight I multiply .452 diameter for the .460 x 1.800 long overall case length. The results is 0.8136. For the .500 case I multiply .500 x 1.625 and  the result is 0.8125 volume. Practically identical for all intent. Possibly the inside diameters are not the same from end to end or case heads are different thickness. ......Paul H

gitano

QuotePossibly the inside diameters are not the same from end to end or case heads are different thickness

That's the only thing I can think of, Paul. QuickLOAD isn't infallible with regard to the specs it reports. I suspect some powder manufacturers make "mistakes" when they give QL their burn rates. This afternoon, I'll measure the volume of some unfired .500 S&W cases I have and report the values here. I don't have any .460 cases to measure.

Paul
Be nicer than necessary.

Paul Hoskins

Paul, I started thinking on the difugilty and sorted out some of the difference Quickload & factory capacity comes in at. I ciphered .250" for head thickness on both cases. This gives the .500 a case volume of 0.687 & the .460 a case volume of 0.700. Still not a lot. Getting old or something. Maybe my brain is shrinking too. :frown.......Paul H

gitano

I measured five (5), unfired 500 S&W cases. (I inserted an inverted, spent primer in the primer pocket to seal the case.) The average weight of the volume of the case was 65.85 grains of water. Converting that to cubic centimeters yields 4.267 ccs. Converting those ccs to cubic inches yields 0.260 cubic inches.

Using a CASE diameter of 0.500" and a CASE length of 1.624 inches. I get a CASE TOTAL VOLUME (capacity plus case wall and head volume) of Pi*(0.500/2)^2*1.624 = 0.319 cubic inches. Converting that to cubic centimeters yields 5.225 ccs.

Now let's come at this bassakwards. The average weight of the empty case was 185.3 grains. There are 15.43 grains in a gram. Therefore, the average measured weight (in grams) of an empty 500 S&W case is 185.3/15.43=12.009 grams. The density of CARTRIDGE BRASS is 8.53 grams per cubic centimeter. Therefore, the VOLUME of CARTRIDGE BRASS in the CASE is equivalent to 12.009/8.53=1.407ccs. Now...

The measured weight of the water in the case is 65.85 grains. Converting that to metric volume we get 4.276 ccs. Converting that to cubic inches we get 0.261 cubic inches of water. Converting the volume of the CARTRIDGE BRASS to cubic inches we get 0.086 cubic inches of cartridge brass. Summing those figures we get 0.347 cubic inches of total volume. Given a TOTAL VOLUME of 0.347 cubic inches we can ask the following question to see how your volume measurements fit the measured data:

If we have a cylinder 0.5" in diameter, how long would it have to be to yield a TOTAL VOLUME of 0.347 cubic inches?

The answer is 1.767 inches. That is 0.142" greater than the actual 1.625" length of the 500 S&W case. (A difference of just over an eighth of an inch - 0.125".) Given that we didn't account for the "negative" volume of the extractor groove, I'd say that's pretty close.

None of which gets to your question of the difference between the .460 and the 500, but until we get actual measurements of a .460 case, we're mostly just doing mathematical "self-gratification".

Paul
Be nicer than necessary.

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