Resizing for Garand surprise!

I discovered something shocking while demonstrating some things to a friend about headspace and gas guns. Apparently what I found is nothing new, but I can't believe that I never saw this anywhere in the years that I have been reloading for my rifle.

I have a series of sized brass that is about 0.001" or 0.002" shorter than the next that I used to measure my chambers to set up my sizing die for my Garands, which conveniently are within about 0.001" of each other...close enough for government work.

Anyway, I size brass to about 0.002" shorter than the longest case that will allow the bolt to close (stripped bolt without ejector). Up until this point all is right with the world.

I show him how fired brass won't fit back in the chamber, how commercial brass will fit without any trouble, how properly sized reloads fit just fine...and then I put in some HXP:

Untitled by jr_roosa, on Flickr

And the bolt barely starts to close!!!

I post this on the CMP Garand forum, and it seems to be old news that HXP runs a little long, but the Garand just smooshes it into the chamber without slamfires, out-of-battery discharges, or any small animals being harmed.

Then, they point to Hatcher's Notebook where it shows that GI .30-06 is supposed to be up to 0.006" LONGER in the shoulder than a Garand chamber, and that some machine guns back in the day had a chamber 0.011" short to MAKE SURE THEY SET THE SHOULDERS BACK ON CHAMBERING to prevent case head separation!

So...this begs the question...what is the optimal amount of resizing? 0.002" short? Same as chamber size? A little long?

Thoughts?

My thought is because I use Winchester primers, that I don't have as much leeway on tolerating out-of-battery slamfires, and I should stick with sizing to about 0.002" short, but I don't think that I'll worry if I get a few in a batch that run long.

-J.

Do you happen to know the actual headspace of your specific rifle?

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Not really. I can estimate it using the Hornady gauge but it has a slight radius where it measures and the measurement it reads comes up short. 2.035" is what it reads but that's incorrect. I'm going to my gunsmith today and I will zero my gauge to an actual headspace gauge so I can convert to real numbers.

1) yes they run long. I had to trim almost all of them and they were once fired.

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Oh, I was talking about length at the shoulder, not trim length.

That cartridge that wouldn't fit is right out of a clip full where none of the 8 will let the bolt close. HXP80 M2 ball ammo.

J.

Do you happen to know the actual headspace of your specific rifle?

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It looks like it is right about 2.050" or 2.051" from what I can gather with putting my Hornady gauge on some actual headspace gauges. Right in the middle of the acceptable range. The Go gauge I looked at was 2.0487" and that measured about 0.002" shorter than the longest case that would allow bolt closure.

I could measure the actual headspace with some other gauges my gunsmith has that run in 0.001" intervals, but I'd have to take down the rifle and strip the bolt, and my curiosity wore out before I got that far.

FYI, the Hornady gauge measures about 0.016" short of what it should, probably because the soft aluminum comparator body has a slight radius at the opening where it measures.

-J.

Certainly the case head on HXP is bigger than winchester. It hasn't been so big to need a small base die for my GI spec chambers. I have heard it won't feed in 1903s.

The sized brass gives me no problems.

J.

Anyway, as I did this morning I measured a pile of factory 30 - 06. They all come up about the same, within +/- of 2.0487". The way I am doing this is I have a RCBS Precision Mic set for 30 - 06. I even checked the set using a Clymer 30 - 06 Go Gauge from my set. I likely have everything here except HXP cases.

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My reloads are at 2.049" or so. HXP goes from 2.047" to 2.054"

J.