Shynloco
I asked my fireforming question here because I was worried my new cases might stretch in the web area and become warped and banana shaped. I asked my question because I primarily shoot milsurp Enfield .303 rifles with chambers the size of blimp hangars. After asking my question here I went back a checked my cases that some of which were over 30 years old that had been fired in my commercial rifle chambers only. I checked them with a RCBS Case Mastering Gauge for thinning in the web area and found no thinning or stretching in the web area (ZERO)
For hunting I would only use new or once fired brass and "NO" special fireforming techniques were used (load as normal and fire) New cases were loaded with loads that were slightly below or near maximum for hunting. The only times I had problems with new brass was when firing commercial cases in military chambers at higher pressures, and these cases would stretch and warp.
Below is a good article on the different resizing methods, accuracy and case life. Also remember you have a standard commercial chamber and the majority of the answers given here are by shooters with competitive rifles with "custom" sized chambers.
"From: bartbob@aol.com (Bartbob)
Newsgroups: rec.guns
Subject: Re: Bottleneck Cases - Seating and headspace
Date: 11 Jan 1996 09:34:11 -0500
Your questions about reloading the .308 Winchester are good.
Headspace for the .308 Winchester, as well as other rimless, bottleneck cases, is measured from the closed bolt's face to a datum point on the shoulder. This datum point for the .308 Win. is .400-inch. Minimum .308 Win. chamber headspace is 1.630-inch. Maximum is about 1.650-inch. New cases typically measure about 1.628-inch from case head to the shoulder's datum point so they will easily fit in minimum-headspace chambers, yet not stretch in firing enough to cause head separation problems when fired in a maximum-headspace chamber. New cases typically end up with a fired-case headspace dimension of about .001-inch shorter than the chamber's actual headspace.
Headspace is measured with steel gages precision ground to specific dimensions. They are put in the rifle's chamber, then the bolt is gently closed. If the chamber is too short and a minimum gage is used, the bolt won't fully close; the chamber must be lengthened with a reamer to fix the problem as new cases may not allow the bolt to be closed. If the chamber headspace is between the minimum and maximum limits,then the minimum gage will let the bolt easily close. If a maximum gage is put in the chamber, the bolt should not be able to close which verifies the chamber headspace is within manufacturing limits for safe use with new cases. But if the bolt closes on a maximum gage, chamber headspace is too long and new cases may rupture if fired in such a chamber. Minimum gages are called "go" gages, maximum gages are called "no-go" gages based on the idea that a the bolt should "go" closed on a go-gage and "no-go" closed on a no-go gage.
Bottleneck sized- or new-case headspace can be measured with a gage such as the RCBS Precision Mic. A case is put head-down in the gage, then a micrometer thimble is screwed on and tightened until it stops against the shoulder. The gage is read in thousandths of an inch. Loaded rounds can also be measured with such gages.
Here's what was learned back in the 1960s about sizing cases. It applies to the .308 as well as other rounds of similar size. Tests were conducted with super-accurate .308 Win. match rifles. Chamber headspace was 1.630-inch,or minimum. Rifles were held in an unrestricted machine rest. An unrestricted machine rest clamps the rifle's forend and butt much like it would be held by someone. On firing, it moves with the same resistance for each shot. It slides on three steel rods riding in V-blocks and moves about 3 inches when fired. The upper cradle is moved back forward against a stop after each shot and repositions the rifle exactly the same for each shot. Such machine rests eliminates all human variables in holding and are commonly used by bullet making companies and military arsenals for accuracy testing. Sometimes only a barreled action is clamped in the rest; pictures of such machine rests are shown in Sierra's reloading manual. The US Olympic Shooting Team uses similar ones for testing .22 rimfire match rifles and ammunition as they know humans can't test them as well as the rest can.
Such tests are much, much better than shooting a highpowered rifle from a bench because of one important, but little known reason. The more recoil a rifle has, the more very, very slight changes in how it's held effect how it moves as the bullet goes down the barrel; very small changes cause the barrel axis to be different for each shot as the bullet leaves. Rifles used in 100 to 300 yard benchrest matches shoot mild cartridges with small powder charges and light bullets which are shot in virtually free-recoil conditions unimpeded by differences in holding which is near machine rest conditions. When held firmly like rifles shooting larger, more powerful cartridges have to be, they typically shoot much larger groups than the sub 1/4th-MOA ones they are famous for. Rifles tested in machine rests typically have groups with smaller spreads between largest and smallest ones than when conventionally benchrested. What this means is that most highpowered rifles actually shoot better than conventional benchrest techniques show.
The .308 rifles fired in a machine rest would shoot about 1/2-MOA test groups with cases sized correctly for best accuracy. Note that twenty or more shots were fired for each group. When hand-held and shouldered from a typical benchrest with the rifle's forend and stock toe on sand bags, the groups would be in the 1 MOA range. Here's a summary of what was learned from these tests.
When a full-length sizing die was set in the reloading press as instructions said, sized cases had a head-to-shoulder headspace typically shorter than a new case. When fired, these cases produced test groups about 1.5-MOA. Note that the die was set in the press such that its bottom just touched the shellholder as the ram was at the top of its movement. This caused the case shoulder to be set back so the sized-case headspace dimension was typically shorter than that of a new case. Such instructions supplied with reloading presses and dies are required for two reasons regarding chambers with minimum headspace dimensions. First, the great variety of chamber sizes for a given cartridge vary quite a bit and the manufacturer wants to be sure sized cases will chamber properly. Second, the amount of case lube applied causes sized-case headspace to vary several thousandths of an inch; lightly lubed cases will have a longer headspace and the manufacturer wants to be sure cases so sized will fit in minimum headspace chambers. Cases so sized could be reloaded about 10 times before their head separation became imminent.
Fired cases partially sized in a full-length sizing die with about three-fourths of the neck sized produced test groups about 1.5-MOA groups. Cases so sized had their body diameter's reduced a couple of thousandths of an inch which moved the shoulder forward several thousandths of an inch. These partially-sized cases were actually longer in head-to-shoulder datum point dimension than the chamber's headspace dimension. A slight binding was noted as the rounds were chambered. Case life of these cases was about 20 to 30 reloads.
Fired cases that were neck-only sized in dies that didn't have their body diameters reduced but their necks were sized down would shoot groups about 1-MOA groups. Subsequent firings of the same case resulted in its shoulder moving forward enough to cause very slight binding as the bolt was closed and groups opened up about 1/4th MOA with such cases. About 30 to 40 reloads per case was possible.
New, never fired cases produced test groups about 3/4ths-MOA even with all their irregularities from manufacturing. The smallest test groups came from cases full-length sized such as the shoulder was not set back from it fired position. Sized-case headspace was the same as, or not more than .001-inch shorter than fired-case headspace. Test groups were about 1/2 MOA. And cases could be reloaded 20 to 30 times.
This well explains why most folks get better accuracy with partial-sized cases using full-length sizing dies than by following press/die instructions for full-length sizing. It also explains why they get better accuracy with neck-only sized cases compared to conventional full-length sizing with the die set according to supplied instructions.
It should be mentioned that the machine-rest tests were made at 600 yards. Had the tests been done at 100 yards, the smallest groups would have been about 2/10ths-MOA and the largest ones about 3/4ths-MOA. In one test, 40 consecutive shots were fired into just under 2 inches at 600 yards. To do that well, the group at 100 yards would have to be about 1/10th MOA.
By using a sized-case headspace gage like the RCBS Precision Mic, you can set a full-length sizing die in a press such that it sizes the cases just enough to set the shoulder back no more than .001-inch. You'll probably get best accuracy this way as well as excellent case life."
