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Old October 11, 2018, 12:32 AM   #26
JohnKSa
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Overall length is limited by what will fit in the magazine. With these cartridges, 357 ROF and 9X23 Winchester, designed to fit in a 10mm or 38 Super magazine, OAL is not going to exceed 1.300" (the OAL of the 9X23), and in some instances that will be too long. 1.300" rounds won't fit properly in my 38 Super magazines without rubbing the front wall.
Correct. The OAL is constrained by the magazine dimensions and in turn, the OAL constrains the case capacity.

So, for example, given a 1.3" OAL limit imposed by the magazine dimensions, the case length could be 23mm (the bullet would stick out about 10mm beyond the mouth of the case when loaded to maximum OAL), 24mm, 25mm (the bullet would stick out about 8mm beyond the mouth of the case with the bullet loaded to maximum OAL), or theoretically even all the way up to 33mm. The last scenario would have the nose of the bullet even with the top of the case--it would look strange and it obviously wouldn't feed very well.

In all of those situations, in spite of the varying length of the cartridge cases, the effective case capacity would be exactly the same. Within the range of reasonable/usable cartridge case lengths for a given magazine size, the effective cartridge capacity (the available space to put propellant) isn't dependent on the length of the case, it is determined by the volume between the inside base of the cartridge and the base of the bullet.

Since the bullet can't be loaded out any farther without making a round that won't fit into the magazine, the space remaining in the case behind the bullet with the bullet loaded to the maximum OAL is what is really important.
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Old October 11, 2018, 05:13 AM   #27
rock185
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John, Thanks for taking the time to attempt to explain that just lengthening the case, if OAL is the same, doesn't somehow result in more velocity at less pressure,etc. I've tried to get that across in discussing the ROF cartridge, as well as other cartridges on other forums. I think you illustrated it best though by the example of increasing case length to 33MM, wouldn't get you any greater effective case capacity. I recall that years ago, Maj. George Nonte wrote of rechambering a Model 39 S&W barrel to .38 Super, then having to deep seat bullets to fit within the Model 39 magazine. I wondered if even Maj. Nonte didn't understand at the time that the longer case, restricted to 9X19 OAL, wouldn't really improve ballistics?

BTW, I agree that the 9X23 Winchester is already filling the slot the 357 ROF is supposed to fill.....
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Old October 11, 2018, 10:25 AM   #28
Jim Watson
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I recall that years ago, Maj. George Nonte wrote of rechambering a Model 39 S&W barrel to .38 Super, then having to deep seat bullets to fit within the Model 39 magazine. I wondered if even Maj. Nonte didn't understand at the time that the longer case, restricted to 9X19 OAL, wouldn't really improve ballistics?
Without digging through my Nonte books, I recall that he used lightweight bullets for that, so he did realize a gain in working volume because the seating depth of a 90 would give a shorter 9mm than the magazine would accommodate and the longer Super would push that back out.

Jerry "Varminter" Gebby pointed out that by rechambering the M39 to .38 Super, the case would gain volume by fireforming into the taper of the residual 9mm chamber. Scary stuff in the pre-Algore days.
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Old October 11, 2018, 11:24 PM   #29
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...I recall that he used lightweight bullets for that...
That would probably work. Lighter (shorter) bullets increase the effective case capacity. Heavier (longer) bullets do the opposite. That's why when a smaller case is asked to perform as well as a larger case by upping the pressure, it tends to have the most trouble performing with heavy-for-caliber bullets.
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