M1 Garand shoulder setback, 0.010" too much for a one time firing?

[ireload2]

The Hornady tool has quirk that can mislead you if you try to use it for direct measurements if you want to compare with the SAAMI drawing. More on this later.

The Hornady tool works fine if you just compare to your fired cases. However the fired cases also vary. Pick 20 to 50 cases and measure all of them. You will find they vary about .002 to .003. This is because the brass temper and the case lengths varied before firing. So find the longest case and verify that it really does chamber in your rifle. Then use that longest case to set the FL die. I set bolt guns used at the range to .000. I set auto loaders .002 shorter. For pumps, lever guns and bolt guns you can determine what you prefer. Ammo used in competition or hunting may be set shorter .001 or .002. Just make sure you check that each setting really works before you load the ammo.

Ok back to SAAMI.

The Hornady tool has a little defect. The functional edge of every one of the bushings has had the edge broken (deburred) by hand. This causes an error on every bushing and because the edge break was done by hand every one of the bushings will be different.

You can get around this if you own head space gages for your rifle.
(Do not to use a .308 gauge with a .30-06)
You have to have the exact shoulder angle.
If you have a .30-06 go gage at 1.940 or 1.942 put the gauge in the Hornady tool and set the dial to the same digits as the gauge length.

If your gauge says 1.942 the dial caliper should be pointing to exactly 1.942 (or what ever is marked on the gauge. Even a field gauge is ok.
Then lock the dial and measure your cases. Your caliper will give you the exact number compared to the gauge and it will be accurate within reason compared to the SAAMI drawing. It will not be micrometer accurate but it will be pretty accurate for calipers because your caliper is only going to measure a few thousandths difference.

Unfortunately you have digital calipers. I don't know how you input a preset number with the digitals. You might have to invest another $20 to get a set that allows inputting the headspace gauge length.


Try it and if you have any problems send me a PM so we can work through it.
I think you will find it pretty simple if you have at least one gauge.

Just remember the shoulder angle of the gauge has to be a perfect match for the round that you are checking.

You cannot use a 22-250 for a 243 or some other combination like that.

If you don't have a gauge find someone who does and get your calipers set and measure a case. Mark that case and keep it for a reference instead of using a head space gauge.

I know I'll catch hell for not checking from the get go and loading 100 rounds and then realizing my mistake, but admittedly I made an error when full length resizing my brass and set the shoulder back too far and now there is between 0.009 and 0.010" of difference in the shoulder of a fired case and the brass I reformed. This is for an M1 Garand using mil-surplus Greek HXP brass (30-06 obviously). I know that the standard most use for bolt guns is either to fire form or leave 0.001"-0.002" but autoloaders should be closer to 0.004" to ensure proper chambering.

*My main question is: Is it safe to shoot this brass this one time to get it back to fire formed size and set my dies properly for the next round of resizing or if I have an unsafe headspace situation that's either dangerous to me or the rifle? Basically will I just be unnecessarily working the brass too much this one time but will be fine or it's not safe and I should just discard the brass?

Also, I've been using a Hornady headspace gauge using a comparator to see how far the shoulder is set back compared to a fired case. The measurements I get (even on other rounds like a non-fired factory case, fire formed, etc) pretty much all come up below SAAMI spec minimum. From what I've learned, this gauge is meant for comparison purposes only and something like the RCBS precision mic is needed to accurately gauge the distance from the case head to proper datum line on the shoulder (and that the measurements tend to read short for everyone due to the design w/ the beveled soft aluminum edge). The SAAMI min-max difference is 0.007" if I'm reading the SAAMI schematic correctly, but again, the comparator style gauge I'm using makes it seem like I'm well below SAAMI and I'm well below the min (could be in....not sure).

*Do I even need to worry about SAAMI spec or is measuring relative to a fire formed case all I should worry about? I assume that if I'm using that brass only in the one rifle then it doesn't matter, but if I wanted to make a round that would fit in virtually any chamber that I should then ensure it's inside of the SAAMI min-max, no?

Sorry for such a long set of questions. I've been hand loading for about two years now and am beyond novice status, but don't want to get careless and do something stupid. I know that excessive an headspace situation (or brass that's out of spec at the shoulder...similar effect) isn't something to be taken lightly. I'd hate to jeopardize my rifle or myself over $50 worth of brass that I should maybe just discarded.

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