Also, is it practical to rebarrel it to .284 Win? I was originaly thinking of a 35 Whelan, but I could change my mind to a .284.
The bad side to this is, it is "safe" only with headspace which still is within the gross maximum. Headspace beyond that requires one of several attacks:
1. Rebarreling.
2. Removal of the old barrel, turning off a thread's-length from the base, reinstallation, finish-chambering to the preferred headspacing.
3. Alternatively, the bolt can be replaced on a try-and-fit basis to see if another surplus bolt will have random dimensions which accidently tighten the headspace.
4. Regardless of the above lines of attack, the engagement surfaces in the receiver for the bolt locking-lugs should be checked for setback. If setback has occurred, correction requires expert attention and perhaps too much expense, followed by more expense for re-heattreating. Personally, I don't think such a drastic project is worth the cost.
If your receiver and barrel are of the same vintage, it would be wise to check the serial number of the receiver against the charts which identify the kind of heat-treating the receivers received. A low-number receiver (which is possible) can be dangerous.
Good luck.
If your Springfield chamber is "tight" enough (short enough in bolt face-to-shoulder dimension) to hold the factory-loaded cartridge firmly enough against the bolt face for the firing pin to consistently set off the primer, and the primers show no signs of "backing out" then being shoved back in the primer pocket upon firing (this ususally shows up as a primer whose base is sread out against the head of the cartridge and exhibits a "flange" on its bottomside when deprimed from the case) then your gun is most likely safe to fire.
All that will happen will be that the case stretches upon firing to match the dimensions of the chamber. This can cause the "ring" approximately 1/4 inch ahead of the rim. This ring does represent a thinned spot in the cartridge head, but if there is no separation on firing, then the case likely still has sufficient integrity to be fired again.
The problem comes when the case is reloaded and the reloader sets the shoulder back substantially from its as-fired dimension in resizing. Upon firing again, the same case stretching as occured on the initial firing will happen again, and the already-thinned brass may split (separate) near the head. To avoid this problem, simply resized the brass only enough to allow it to adequately grip the bullet and to chamber without undue resistance in turning down the bolt handle.
Think of it this way: The chamber has excessive headspace only with factory-dimensioned cartridges. With cases fired once in it, the headspace is, by definition, perfect.
My guess is that the headspace of your Springfield is probably no different than when it left the armory. Military rifles usually have fairly generous chambers to allow them to work with dirty ammunition fouled with sand, grit, and other trash which may be picked up in battlefield conditions. If it doesn't split a factory load on the first firing, it's likely o.k.
One way to make absolutley sure that a rifle with excessive headspace can be fired safely is to load cartridges for the initial firing, or fireforming in this case, with the bullet seated out long so that it is pushed firmly against the lands of the barrel upon chambering the shell. This will, in effect, headspace your round on the bullet rather than the shoulder of the brass.
Use a slightly reduced load of powder since the chamber pressure will usually be increase somewhat with a bullet pressed against the lands. Upon firing, the case will stretch from the base forward, rather from the middle backward, and you will end up with no thin place near the critical web area of the case -- and with a case which fits your chamber like a glove.
When surplus Springfields were rather common, you would hear warnings about the weak receivers of "low numbered" Springfields. These "weak" receivers were actually too hard, having received a heat treatment that sometimes made them too brittle. They could, and did at times, crack. But the hard receiver of a low-numbered Springfield would never show set-back in the locking faces which would allow headspace to grow. A soft bolt, on the other had, could suffer locking lug set-back after many, many rounds (and perhaps wear-grinding from being operated dirty).
I'm just down the road in Georgetown. Drop me a line if I didn't explain myself well enough and you have questions.
I would also seek to find out why I had headspace to start with...
the cases you have fired may be safty suspect...
An alternative to seating your bullets way out is to neck up the cases a bit (say to .338) and neck them back down, but leave a little secondary shoulder at the base of the neck. Some trial-and-error will indicate how much shoulder you'll need to hold the case against the bolt face. The result is the same.
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Ray Atkinson