Home Forums Hunting & Shooting Ask The Gunwriters How much shoulder is needed for headspacing?

Mr. Howell;
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<br>How much greater in diameter need the shoulder of a case be than the case neck for reliable headspacing? I am thinking of a 35-40 degree shoulder and looking for the minimum diameter difference for sound headspacing.
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<br>Fireplug

Fireplug:
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<br>Ken is on the road, due home Saturday. In the meantime we'll keep you entertained until he gets here.
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<br>The short answer is that NO shoulder is required to headspace. Some cases headspace on the case front neck rim. These are usually pistol cases.
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<br>Naturally you know that some cases headspace on the belt and some headspace on the rim. A case is also tapered so there is a point where it will not move any further foreward. That point could be beyond the no go sign but the very smallest shoulder could be related to the thickness of the belt on a belted magnum. If a belted magnums belt will headspace acceptably, by the same token a shoulder equal in size should also work.
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<br>If the rim on a rimmed case will headspace then a shoulder of the same width should also be acceptable.
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<br>Bill Tibbe

Sorry but the wrong answer is that "no shoulder is required" when we are discussing 35-40 degree angles.
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<br>The 300 Savage works with .050" on a side and a 30 degree angle. That seems to be where to work from.

I'd be irresponsible if I tried to cite you a single numerical figure.
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<br>Whether the difference between two diameters applies to belted, rimmed, straight, or necked cases, the minimum effective difference depends entirely on the fit of the loaded case inside the chamber.
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<br>To illustrate the point, consider the force required to overcome the resistance of a sizing die, to make it "accept" a fired case. In this extremely snug "fit," the difference between the diameters of (say) fired .38 Special brass and a .38 Special case that can freely enter a .38 Special sizing die is very small. The headspace ledge in the mouth of a .30 Carbine, 9mm Parabellum, .423 OKH, .444 Marlin Rimless, or .45 ACP chamber isn't very wide, and the sized case has to fit into the chamber pretty snugly.
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<br>The shoulder on a fire-formed .400 Whelen is adequate. The shoulder on another .400 Whelen case (NOT fire-formed) can be inadequate. Nominally, the difference between shoulder and neck diameters is only 0.024 inch (0.454 - 0.430 inch). The nominal shoulder angle becomes irrelevant in such a case, because the convex fillet at the base of the shoulder and the concave fillet at the base of the neck leave no straight line there to form a true angle.
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<br>As a practical figure, the difference between the neck and shoulder diameters of UNfire-formed brass in an anonymous or typical chamber would have to be a bit more than the 0.024 inch that headspaces the fire-formed .400 Whelen case quite adequately.
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<br>The nominal difference between the belt and body diameters of the H&H Magnum cases isn't much, either -- less than 0.020 inch (0.532 - 0.513 = 0.019 inch). If the shoulder of a SIZED necked case fits its chamber as closely as the base of a magnum case fits its recess, the same slight difference in diameters should be adequate to hold the case against the impact of the striker -- which is, after all, cushioned somewhat by the relative softness of the primer cup as it indents under that very localized impact.
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Thanks All,
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<br>I noticed that among factory rimless and beltless (you are making me be more specific) round the .35 Rem. has the least differential at .044, but as noted some wildcats have less.
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<br>My .416 TAS project has run into some diificulty due to the very thick case walls of the .240 Weatherby (.035 were even the hotest other rounds are about .029) limiting powder capacity. I hate to go to the step of reaming each case to a more typical thickness. I thought I might look at a rimless case formed from .308 with its' much thinner case, but after stuffing a .416 bullet in there it is darn close to the case's diameter.
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<br>Thanks Again,
<br>Fireplug