BruceB
05-02-2005, 11:55 PM
"Headspace" is a term all new handloaders must confront, but most of us old f---s have learned to deal with it as a matter of routine.
I had an interesting demonstration of its influence once again just this afternoon.
Loading up a bunch of .30-06/311299 for the Nevada Shoot, I was using a new RCBS Small Base sizing die which I picked up to load ammo for my Garand. I've loaded MANY rounds for Garands and other .30-06 rifles with a standard die, but I decided to go with the SB anyway.
So....I set up the dies, and checked the first cases with a Wilson case gauge, which has the maximum-minimum surfaces machined on each end to indicate how well one's sizing die is adjusted, and also to gauge case length. The first cases were just about right, being between the max/min dimension "shelves" on the gauge, so I commenced turning out ammunition.
About 120 rounds into the run, it occurred to me that it would be a pious thought to actually check how the rounds would fit in the rifles....three rifles, to be exact. The differences in the chambers were immediately apparent. In my Model 700 BDL, the rounds fit with just a nice wee bit of "feel" as the bolt cammed into lockup. In the Garand, they were a bit snugger, and this is DEFINITELY NOT a good thing, as rounds for these rifles must chamber freely to minimize any slam-fire possibilities. In the '03 Springfield, it took serious effort to get the bolt locked.
So, I have 120 rounds which fit the 700 about perfectly. Since the sizing die was screwed down tight enough that it took a definite "bump" for the ram to make full travel, I had to find a route to size cases for the other rifles a tad more than the setup was giving me. I tried an assortment of shellholders and found a couple thousandths' difference among 'em, but not enough to give the sizing I wanted. Taking the "thinnest" shellholder, I ground some material off its top until I did get enough extra sizing to do the job for the Garand and '03. Even when the maximum of sizing is applied, bumping the die hard on this altered shellholder, the cases are just at the "minimum" dimension on the case gauge, and now the rounds chamber freely in both rifles. That is, I can't go BELOW the minimum shelf, meaning that I'm not producing rounds with excessive headspace. Rather, they are on the short side of the normal tolerance of headspace range, and now fit very nicely in the chambers.
The altered shellholder is CLEARLY different from the others in stock, so there'll be no problem sorting out which one I need for the more-extreme sizing. Come to think of it, I'll store this shellholder in the same box as the SB die for future reference.
My original set of RCBS dies gave no such dimensional troubles. It's just the addition of the one new sizer which led to this, and I suspect the die is well within tolerance, as shown by the good fit in the Remington. I DO find it curious that the two military chambers are tighter-headspaced than the commercial one in these rifles, but "facts is facts". I woulda thunk it'd be the other way around...looser military chambers. BTW, the base diameter of cases from the SB die is about .003" smaller than cases sized in the "regular" die.
I had an interesting demonstration of its influence once again just this afternoon.
Loading up a bunch of .30-06/311299 for the Nevada Shoot, I was using a new RCBS Small Base sizing die which I picked up to load ammo for my Garand. I've loaded MANY rounds for Garands and other .30-06 rifles with a standard die, but I decided to go with the SB anyway.
So....I set up the dies, and checked the first cases with a Wilson case gauge, which has the maximum-minimum surfaces machined on each end to indicate how well one's sizing die is adjusted, and also to gauge case length. The first cases were just about right, being between the max/min dimension "shelves" on the gauge, so I commenced turning out ammunition.
About 120 rounds into the run, it occurred to me that it would be a pious thought to actually check how the rounds would fit in the rifles....three rifles, to be exact. The differences in the chambers were immediately apparent. In my Model 700 BDL, the rounds fit with just a nice wee bit of "feel" as the bolt cammed into lockup. In the Garand, they were a bit snugger, and this is DEFINITELY NOT a good thing, as rounds for these rifles must chamber freely to minimize any slam-fire possibilities. In the '03 Springfield, it took serious effort to get the bolt locked.
So, I have 120 rounds which fit the 700 about perfectly. Since the sizing die was screwed down tight enough that it took a definite "bump" for the ram to make full travel, I had to find a route to size cases for the other rifles a tad more than the setup was giving me. I tried an assortment of shellholders and found a couple thousandths' difference among 'em, but not enough to give the sizing I wanted. Taking the "thinnest" shellholder, I ground some material off its top until I did get enough extra sizing to do the job for the Garand and '03. Even when the maximum of sizing is applied, bumping the die hard on this altered shellholder, the cases are just at the "minimum" dimension on the case gauge, and now the rounds chamber freely in both rifles. That is, I can't go BELOW the minimum shelf, meaning that I'm not producing rounds with excessive headspace. Rather, they are on the short side of the normal tolerance of headspace range, and now fit very nicely in the chambers.
The altered shellholder is CLEARLY different from the others in stock, so there'll be no problem sorting out which one I need for the more-extreme sizing. Come to think of it, I'll store this shellholder in the same box as the SB die for future reference.
My original set of RCBS dies gave no such dimensional troubles. It's just the addition of the one new sizer which led to this, and I suspect the die is well within tolerance, as shown by the good fit in the Remington. I DO find it curious that the two military chambers are tighter-headspaced than the commercial one in these rifles, but "facts is facts". I woulda thunk it'd be the other way around...looser military chambers. BTW, the base diameter of cases from the SB die is about .003" smaller than cases sized in the "regular" die.