Belted magnums- to go, or to no-go? That is the question.

[bigedp51]

NWChapman

I agree 100% with what stangfish has said above and I'll tell you why, the average full length resizing die when making hard contact with the shell holder (cam over) will push the shoulder of the case back .002 to .004 "SHORTER" than minimum headspace or the GO gauge. (some dies will push the shoulder back even further)

The most case stretching and thinning in the base web area happens the first time the case is fired so tight headspace increases case life and accuracy. When I say accuracy I mean the tight headspace helps prevent the case from stretching and distrorting on the first firing and also prevents the warped and banana shaped case. (see 1,2 and 3 below)



If you look at the circled items below that govern headspace you can see at "maximum" headspace and minimum manufacturing tolerances you can have .015 head clearance or "excess" headspace. Even if you could set the headspace to minimum or the GO gauge and then run into a case at minimum dimensions (cartridge headspace) you could have .008 head clearance on a brand new case. Therefore proper fireforming might be needed depending on your new cases "cartridge headspace length" in relation to chamber headspace.



Trust me, I have seen much worse before. (rimmed and belted cases are the worst offenders)

Below a .303 British case that is over 1/8 of an inch short of manufacturing tolerances for shoulder location.



Below, how much longer the military chamber of the Enfield rifle is than American SAAMI specifications.



Knowing the exact length of your chamber and then "MINIMUM" full length resizing for "YOUR" chamber is critical for case life and accuracy.

Below, .308 cases were full length resized and making hard contact with shell holder (cam over) when resized which means they were "over" resized and the shoulder of the case was pushed back too far during resizing.



Please note the amount of stretching listed below and when the case failed and separated. The cases below didn't stretch on the first firing "BUT" the shoulder of these cases were bumped back too far during resizing and this caused the cases to fail.



NOTE: I have seen brand new belted and rimless cartridge cases that were much shorter than minimum manufacturing tolerances. These are the cartridge cases that need fireforming at lower chamber pressures to blow out the shoulder to fit your chamber and not allow any case stretching and thinning in the web area.

I use a RCBS Case Mastering Gauge to check for stretching and thinning in the base web area.



I also have GO gauges for most of my rifles, and I use them as a zero reference point with my cartridge case gages. This lets me know my chambers exact headspace setting and allows me to full length resize with minimum shoulder bump.



NOTE: The Hornady cartridge headspace gauge above is a "must have" and will fit every caliber you own, and in the end cost much less than separate gauges for each caliber.