308 Winchester Headspace Dimensions

[GuitarXM]

Does anyone know what the minimum and maximum head space dimensions are for .308 winchester?

I think my resizing die is setting the shoulder back too far...
My head space measures .004 under 0 on the RCBS micrometer, where 0 is supposedly the minimum head space dimension...

My die is currently set up to touch the shell holder and screwed in 1/4 turn because its a steel die...
I read online that you have to back the die out, but I don't understand how that solves the problem because if I back it out, it will still touch the shell holder...

And say if I back it out, to where it doesn't touch the shell holder, wouldn't it not resize the bottom portion of the case next to the head??

[F. Guffey]

Head space, a necessary thing, in the perfect world the difference between the perfect commercial/military case is .005 shorter from the head of the case to the shoulder than the chamber length from the face of the bolt to the shoulder of the chamber. Measurement are said to be taken from 'the datum line' the datum is not a line, it is a circle or hole, the 308 Winchester circle/hole is .400 in diameter, the distance from the datum (circle/hole) back to the head of the case is 1.634, the chamber in the perfect world is 1.634 + .005 or 1.639, I make gages, I make up DAT-UMS, for the 308 Winchester 3/8" (.375) works.

This does not work for everyone, I do not grind shell holders, I do not grind dies, when I size a case with the die adjusted down to the shell holder with an additional 1/8 turn, I size a perfect case that is .005 shorter than the perfect chamber.

Minimum/Maximum, I do not have one, I adjust my dies when I size to avoid sizing, in the perfect world the no-go gage is .004 thousands longer than the go-gage (which is .005 longer than the perfect case), If the perfect case is fired in a chamber that is no-go gage length, the head space will be .009. Beyond that there is the field gage, the field gage is .014 longer than the perfect case, when the perfect case if fired in the field gage length chamber there is .014 head space, I have one 30/06 rifle that has .016 thousands head space, when I fire it there is .000 head space, I make gages, I size cases to fit the chamber.

F. Guffey

[Bart B.]

SAAMI says: 1.630 GO, 1.634 NO GO, 1.638 FIELD

Which means that new rimless bottleneck factory cases (loaded or unprimed) hafe to be shorter than the GO one; less than 1.630 inch. New cases are typically between 1.625 and 1.629 inches. Best accuracy and very long case life (as much as 90 or more with some cases) with rimless bottleneck cases is usually done when sized case headspace is about .004-in. shorter than chamber headspace, not the zero point on the case headspace gage.

Find out what your rifle's chamber head space by using the RCBS Mic to measure a fired case. If it reads + .002, that means the fired case headspace is .002-in. greater than minimum, or GO, but still within the NO GO normal limits. There's usually a couple thousandths between fired case headspace and chamber head space.

Screwing down your sizing die 1/4th turn moves it about .018-in. But it'll be pressed back up when the shell holder atop the ram pushes it there at the top of the stroke to size a case. One normally doesn't need to screw their die down that much to have the shell holder touch the bottom of the die holding the case.

[GuitarXM]

I am a little confused....
Whether you screw die in 1/4 turn or not...the die is still set up to touch the shell holder...Correct?

What I am asking is, if you bring the shellholder all the way up, and then screw the die out so it doesn't touch the shell holder say 1/2 a turn back..

So now there is a little space between the shell holder and the die...
Wouldn't that affect the sizing of the bottom portion of the case?

I am asking about this..because in a reloading video that I watched, the guy says that if your die is sizing more than .002, you should screw the die out a full turn, and then screw it in in increments until it sizes .002...

[F. Guffey]

I have confidence in my press, my press is not 'springy', the additional turn after contact is said to remove the spring (deflection) in a springy press, when the shell holder is contacting the bottom of the die (ram up and crammed over) there is no room for anything between the die and shell holder but the case with nothing hanging out. if there is something hanging out I can measure it, but it has has to be one tough case. When the case is removed from the press after sizing it has to be a full sized length case, I can full length size a case + meaning I can full length size a case that is .012 under a full length sized case (,017 thousands under a go-gage size chamber if necessary, when cutting a chamber, I find it necessary).

As to backing a die out a guesstimate of a turn, I adjust the gap between the shell holder and bottom of the die with a feeler gage, if I want to size a case for a chamber that has .006 head space, I use a gap of .005 thousands, seat a bullet, chamber and check for fit. You will never get through purchasing tools, in my opinion the best investment you can make is $11.00 for a machinist feeler gage.

If sizing is nothing more than adjusting a die down an additional 1/4 turn after contact or backing off a guesstiment, what is the purpose of purchasing gages that measure something that is not used to transfer to the press.

The man said in the demonstration? He should have said back the die out .7142857 (one turn) and then turn it down or in until it sizes cases .002 over minimum length, I will take a liberty and say WHAT AN IDIOT! Why not adjust the die down until it makes contact, then adjust the gap with a feeler gage, after contact, back the die out, insert the feeler gage, scres the doie down until it contacts the gage, secure the die lock nut, and then check the gap, with the feeler gage.

F. Guffey

F. Guffey


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[Bart B.]

I've got an RCBS Jr. and two Rockchuckers. Each one has some spring to it. 'Tis the nature of those things. How much can be measured with a dial indicator. It varies with the type of lube, how much lube's on the case, how thick the case walls are, and the difference between fired case and internal dimensions of the die.

The slightest amount of lube results in shoulders being set back very little; the press will spring quite a bit. With more lube, shoulder setback is more as the press springs less.

Each of my several .308 Win. RCBS full length sizing dies will have different clearances between their bottom and the shell holders to size cases to a given case headspace. This was verified by putting a chamber head space gage in them and measuring the difference between gage head and the bottom of the die. These dies also vary a couple thousandths in body diameters so the smaller ones size case bodies a bit more than the larger ones.

I've put each one in the press, put my .308 Win. "go" gage (1.630-in.) in the shell holder, raised the ram then screwed the die down to just stop with its shoulder against the head space gage shoulder, locking it in place. Each die has a different gap beteen its bottom and the shell holder. All cases sized with this set up have longer headspace than the gage by some amount; proof that there's some spring in the press.

I tumbled my deprimed and cleaned brass in a foam lined can coated with thin film of lube. This way, all the cases have a narrow range of sized headspace; typically .002-in. Every time I've tried rolling cases on a lube pad or other such surface, the amount of lube varies so much across the cases that they'll have a lot more spread in headspace. Cases sized too much with too short of headspace typically didn't shoot as accurate. And, of course, way too much lube will dimple the shoulder.

Another interesting thing I've noticed is case weight can effect their sizing for a given setting of the die in the press. Sizing WCC-58 commercial cases weighing 150 grains, those thin cases will have a lot of shoulder set back for a given amount of lube on them. In contrast, really heavy cases such as M118 or M852 match ones weighing 30 to 40 grains more don't get as much shoulder set back sized the same way.

[F. Guffey]

The .07142857 represents (travel/distance) one turn of a die in a press with 14 threads per inch, 1/4 turn represents .01785714, 1/8 turn represents .008925871, 1/16 represents .004464286, without a degree wheel, why make guesstimates, if the thread on the die was 10 tpi, 1 turn would be 1/10 of an inch or .100, again how would you check the guesstimate adjustment, again, I use a feeler gage and eliminate the guesstimate adjustment.

Your revised question: the bottom of the case is not sized, the deck height of the shell holder is .125, the bottom of the die has a radius, add the radius to the .125, this leaves as much as .135 of the case that can not be sized, when chambered the unsized portion of the case is referred to as case protrusion, case protrusion, the part of the case that is not supported by the chamber is not absolute but .110 is a good number for a 98 type Mauser, that leaves the web, the web thickness starts? at .200 for military 30/06 brass and is as thick as .265 for commercial brass, the web is not part of the thin body of the case, the web is solid, at this point we have to consider someone is doing something very wrong when the web requires sizing, if this is true we have to consider at least .200 plus of the web does not get sized.

In my opinion adjusting a die with fractional turns is busy work and the person that can not get beyond this method/technique starts over every day and always need another tool, which is not all bad, but after they acquire another 'checker' tool, how do they transfer the results to the press without a standard/transfer, the feeler gage is a standard/transfer/gage.

IF (big if) RCBS, Lyman, Redding, Lee, etc., make a precision dies, I believe they do, the cavity created when a die is placed on a shell holder represents a perfect cavity for the perfect chamber, variations: cases resist being sized, presses deflect (Spring), thus the additional 1/4 turn after contact. I am not trying for the perfectly sized case, I want a case that fits my chamber, and I do not have a 'springy' press, I have heavy presses for heavy work, and when it is important I hesitate, the ram being up dies not mean sizing is complete, the brass could still be compressing and conforming to it's new shape.

[Bart B.]

Mr. Guffey, have you ever measured fired versus resized case head space with tools such as the Stoney Point gage or RCBS Precision Mic?

[a7mmnut]

Where is the brass going? You should be able to mic the case and mouth wall thickness and tell if it's in spec. or not. I would think pushing the shoulder back would flow brass longer into the neck. Also, brass will easily contract or expand with varying degrees of hardness and temperature. If you already have a fire formed brass, are you comparing the shoulder length dimension to your gage or to the die? I have measured freshly fired brass and thrown them into a freezer or warmed them up with a blow dryer. There's quite a bit of variance between brands. Military annealed brass seems to be the hardest, but not necessarily always. Personally, I'd switch brands of brass and retry. I'm not a match loader, but I have loaded many hundreds of rounds of .308 in Lyman, Lee, and Hornady dies. Each one chambered well in my now reminiscent M70 and my newer guns as well. Good luck, and please post your results. -7-

[GuitarXM]

What is the spring tension you are referring to?
Is that the tension the press will place on the case after full length sizing, meaning case fully inside die and the die is touching the shell holder?

I have a lee hand loader, so the way my die is set up, is 1/4 turn in..
Basically I can't close the hand loader fully...There is a 1/4" gap between the 2 levers of the press...

By the way, I don't have fired brass yet...
This brass was resized because I had to use the die's expander ball to make the neck uniform, so I can load it for the first time...

I know that I will want to set up my die to set the shoulder back .002 in order to give my brass more reloadings....

So what I was asking was...is that when you start to turn the die out, it will still touch the shell holder, because I have a 1/4" gap created between the two levers of my lee hand press. It was originally set up according to the instructions to touch the shell holder and create a 1/4" gap between the levers to remove this spring tension I guess? I don't know...

So when you guys talk about screwing the die out, that would mean that the 2 levers of my press would have to make contact, and there will be a space between the shell holder and the die? Then I would adjust in increments until I see a .002 reduction in head space?

Am I understand this correct?
I know that the more accurate way would be to use a guage.

[Bart B.]

a7mmnut asks: "Where is the brass going?"

Dug out a data sheet I made in the early 1990's to refresh my mind. Filled it out when at a friend’s underground 100-yard range with complete reloading facilities 4 feet from the concrete shooting bench. This was part of a test to see how many reloads we could get from a case with maximum charge in a standard SAAMI chamber headspaced at 1.631-in. The pre-64 Winchester had a 26-inch Hart barrel with .2999 bore, .3078 groove and the chamber neck diameter was .345 inch.

The RCBS full length sizing die had its neck lapped out to .335, a .270 expander ball was used as the neck didn’t need any expanding, its shoulder diameter was .452 and its diameter at the pressure ring point (about 1/10th inch inside the die) was .469-inch. He did the shooting and I did the measuring and reloading. A shot was fired about every 2 minutes.

Here's where the brass went when I gook a new Federal .308 Win. case, trimmed its length to an even 2.000-in. case length (CL), primed it with an RWS standard primer, metered 42 grains of IMR4895 in it, then seated a 165-gr. Sierra SPBT bullet. This new case had a pressure ring (PR) diameter of .468, shoulder diameter (SD) of .451, loaded round neck diameter of .337 and a case headspace (CH, base to shoulder datum) of 1.627-in. The following's a summary of what happened starting with the first firing (1st F) and first reload (1st R):

Orig; CL=2.000, CH=1.627, SD=.451, PR=.468

1st F; CL=1.998, CH=1.630, SD=.456, PR=.473
1st R; CL=2.001, CH=1.628, SD=.453, PR=.471

2nd F; CL=1.998, CH=1.630, SD=.456, PR=.473
2nd R; CL=2.001, CH=1.628, SD=.453, PR=.471

3rd F; CL=1.999, CH=1.630, SD=.456, PR=.473
3rd R; CL=2.002, CH=1.628, SD=.453, PR=.471

4th F; CL=1.999, CH=1.630, SD=.456, PR=.473
4th R; CL=2.003, CH=1.628, SD=.453, PR=.471

5th F; CL=2.000, CH=1.630, SD=.456, PR=.473
5th R; CL=2.003, CH=1.628, SD=.453, PR=.471

6th F; CL=2.001, CH=1.630, SD=.456, PR=.473
6th R; CL=2.004, CH=1.628, SD=.453, PR=.471

7th F; CL=2.002, CH=1.630, SD=.456, PR=.473
7th R; CL=2.005, CH=1.628, SD=.453, PR=.471

8th F; CL=2.003, CH=1.630, SD=.456, PR=.473
8th R; CL=2.006, CH=1.628, SD=.453, PR=.471

At this point, the case was trimmed back to 2.000-inch and we continued. The same data repeated for every 8 to 9 shots. Measurements were to the nearest 1/1000th inch; any finer was not practical nor useful in this experiment. After 47 shots and reloads on this one case, we ran out of powder. Muzzle velocity at 20 feet was about 2635 +/- 13 fps across all 47 shots.

Here’s what I surmised from this test:

* Cases get a bit shorter when fired, then lengthen a bit when sized. This is where the brass goes. They do need occasional trimming back to a decent starting length.

*Annealing case necks isn’t needed if the case neck’s not sized down and expanded any more than needed.

* Full-length sizing done just enough to set the shoulder back and reduce body diameters a couple thousandths from its fired position prolongs case life.

A friend of mine did this same test loading on the range shooting them in his Hart barreled rifle clamped in a machine rest. He ran out of powder from his partially filled can after 65 shots starting with a new Winchester .308 case. All 65 shots went inside 1/3rd inch at 100 yards. His data compared almost identical to mine.

[Slamfire]

I set up my sizing dies with Wilson type cartridge headspace gages. To verify that this cartridge gage was cut correctly, I inserted chamber headspace gages into the thing.

The lower ridge corresponded to the Go gage and the upper corresponded to the No Go gage.

The Wilson cartridge headspace gage is cut wide between the shoulders and the base, so you can insert a fired case and measure the actual headspace of your chamber. The Wilson gage measures "length", not "fatness".

Anyway, I set up my dies so the cases are sized to gage minimum. I have had dies that would not size the case to a minimum headspace. The die body was too long, so I ground material off the base. It worked.

[Bart B.]

GuitarXM asks: What is the spring tension you are referring to? Is that the tension the press will place on the case after full length sizing, meaning case fully inside die and the die is touching the shell holder?

It's the amount the press top that holds the die pushes up from friction between the case and die as the ram goes up. With an empty die is adjusted to just touch the shell holder, when a lubed case is pushed up into the die all the way, the bottom of the die will be a few thousandths above the shell holder. This springiness is only in the vertical or die/case axis.

I've watched the die slowly come back down a tiny bit as the ram's still all the way up. That's just the spring pressure of the press pulling the die further back down the case.

"C" presses usually have more spring than "O" types as there's more metal holding the top part where the die's at. Lee hand loaders may have very little spring.

One really should use a gage to measure fired cases then again after sizing them. Otherwise, the actual amount of shoulder set back could be several thousandths off from what one wants to get. The amount and type of case lube plus any spring in the press will greatly effect the gage readings after sizing.

[Unclenick]

GuitarXM,

"Touching the shell holder" applies to it touching with a case pushed all the way up into the sizing die. When you back the die out a little it will still touch the shell holder when it is empty, but when you have a case forced up into the sizing die, you can often begin to see a crack of light between the top of the shell holder and the bottom of the die when you don't have that full 1/4 turn over. This is due to the press stretching a little elastically. It is normal for all but very beefy presses. No harm is caused by it as long as it is consistent. That is the "spring" that was referred to.

The case head normally does not expand during firing. At normal pressure the head is too thick to do that, so it doesn't need resizing. Only the portion of the case above the head does. Thus you have some leeway with your sizing die adjustments. Normally, for smooth magazine feeding, you only need to size the case so the shoulder is set back about 0.002" shorter than it is after it has been fired (which leaves it pretty close to the size of the chamber). If you look at SAAMI chamber and cartridge case specifications, you will see the minimum headspace for a chamber is typically about 0.002" longer than the maximum headspace length on a new cartridge case because that is adequate clearance.

Your Precision Mic is supposed to land on zero when measuring a fired case that has been fired in a chamber that has SAAMI minimum headspace. In other words, it is intended to measure to gun headspace indirectly off a fired case. My .308 Precision Mic proved to be off 0.002" at zero when I put a good quality (Dave Manson) headspace GO gauge in it, so you can't count on the absolute accuracy of it. It is excellent for comparative readings, though, and that's what you want for setting up a full length sizing die.

A new case being 0.004" short of chamber headspace zero is within commercial tolerance, so don't worry about that. The main reason for sizing just 0.002" below the chamber headspace zero is to maximize case life. Less stretching means less likelihood of head stretching enough to separate from the rest of the case. Measure a fired case from your chamber on the PM, then set your sizing die to produce a case with its shoulders 0.002" back from there. If that turns out to be above where the die touches the shell holder, that's OK. If the fact it isn't touching makes you uneasy, Redding makes sets of shell holders with extra thickness of their case retaining lips in 0.002" steps so you can touch down and have a longer case both. It makes setup and adjustment a bit quicker.

[GuitarXM]

You guys are the best. Thanks.

[Bart B.]

unclenick:

Your Precision Mic is supposed to land on zero when measuring a fired case that has been fired in a chamber that has SAAMI minimum headspace. In other words, it is intended to measure to gun headspace indirectly off a fired case.

99% of your comments were great. Except for the above.

The RCBS Prec. Mic for rimless bottleneck cases should read zero when a GO headspace gage is in it and the thimble closed against it. According to RCBS, it's only going to measure what case headspace is; new, fired or resized. They use a GO headspace gage in the Mic then turn the Mic head against the gage gently until it stops. Then they turn the thimble until it zeros on the index line and seal the thimble on its gaging head with epoxy.

A case whose headspace is shorter than actual chamber headspace will still be shorter than chamber headspace after it's fired. Typically 1 to 2 thousandths of an inch shorter with normal max loads. Fired cases with reduced loads will be even shorter, sometimes as much as 10/1000ths shorter in tests I've run.

[GuitarXM]

K...So I tried to determine bullet seating depth 2 ways and encountered a problem which I hope is not that serious...

First method I used was a method recommended to me by seating a bullet in increments until it falls freely from the barrel. My first cartridge measured about 2.9. I colored the bullet and put it in the chamber by hand and by closing the bolt...the result was that it fell out and didn't stick. I know that its suppose to stick or you should at least see contact marks on the ogive which I didn't see..
Plus at 2.9, it will not fit in the magazine...

So this method failed for me..

I then used the fake bullet from the RCBS micrometer.
I made the bullet long so it can make contact when I put it in the chamber...I put it in the chamber by hand and it gave me a reading of 0.035-0.040 on the micrometer using the land nut..

I then tried to put the dummy bullet in the bolt and close it with the bolt, which was unsuccessful because it gave me a higher reading..1.035 something like that...So I'm pretty sure thats wrong...

This is where the PROBLEM happened.
I was doing multiple trials, by putting the dummy bullet in by hand into the chamber, and one time, I think i pushed too hard, and the entire dummy bullet, including the head went inside the chamber...

So now I'm scared that I might have damaged the chamber..
I mean I tried to put the dummy bullet in and its fine...It takes a considerable amount of force to force the dummy bullet inside the chamber?

I mean WOW..I am an idiot for sure for putting pressure on the bullet...
What do you guys think the outcome of this mistake? Did I damage my chamber?

So to continue the story...I started seating an actual 168 gr bullet into the case and would then check it on the micrometer land nut...

I know that you cant really compare the ogive of the real bullet and the ogive of the dummy bullet, but I had no choice...

So according to the micrometer, my bullet seating depth was .035-.040...
I got the real bullet to a depth of .015, hoping that it would be .020 off the lands.

I then measured the actual bullet with a caliper and it was perfect...It was 2.800, which is the max OAL. I then checked it in the magazine and it was fine...

Another test, I did was a bullet seating test I learned from a video..
I used my sneaker's laces to pull on the bolt, put a dime in there, and took the spring out....lol

I put the bullet in the chamber and put the bolt without the spring in the rifle... The video says that when u close the bolt, you should have like a pound of force...If its more than a pound, then you need to seat the bullet deeper...I would say it was around 1-2 lbs.....

Any advice on bullet seating and chamber damage?
Hope I didnt kill it.

[F. Guffey]

"I have a lee hand loader" Allow me to ask a question, Is your press mounted on a table? Lee made kits for reloading, Lyman (Ideal) made kits for reloading that did not use a table mounted press.

Determining maximum Over All Length, OAL: You can purchase a lot of tools are you can get more use out of your cleaning rod, or wood dowel, drill the flash hole/primer pocket to a diameter large enough to allow the cleaning rod to pass through it, size the case, seat a bullet, remove the bolt, chamber the test round, insert the cleaning rod in the flash hole and push the bullet out until it stops, this will give you maximum (OAL) length, this does not mean the case will feed, it could be too long, I have tested chambers with this methods and pushed the bullet out of the case before the bullet hit the rifling, what was the builder thinking, he made the reamer, used Remington 03A3 rifles, used Western stocks and built built 5 7mm Gibbs, one rifle came back, we took it to the range, it was very accurate with a narrow selection of bullets and powder, to either side the 'groups' became 'patterns'.

If you drill the flash hole out on 20 cases, you can use this method to make test cases for various types of bullets, and, use the test cases for adjusting the seater die to '0', then, use a depth micrometer to adjust the seater plug stem height, by zeroing the micrometer before you start you can adjust the OAL by adjusting the stem down and read in in .000 thousands. Others shred the case neck and use one case.

Then it is back to head space, head space can be added to to the length of the case between the head of the case and shoulder, this same dimention can be added to the max OAL, Again I have a 30/06 M1917 with .016 head space, meaning I can start trimming when the case gets to 2.208.

Bart B. I have tools that never get out of the box, I have head space gages, Wilson case gages etc., I choose to use gages I make, nothing I shoot or build shoots gages, you mentioned a WCC 58 Commercial case, if I had one it would have started out as a WCC 58 military case, and yes WRA, WWC and WCC cases were lighter than other cases. I have 30/06 military cases that became 308 Winchester cases, in the process while forming I could have stopped at 8X57, 7X57, 7.7 Japanese, 257 Roberts, there is no secret about stopping, I choose to stop sizing just before the shoulder is set back to the point the case will chamber, after that it is a matter of adjusting the die to the shell holder. Again on another forum a man wanted 7.7 Japanese cases, I formed 60 cases using 30/06 new, commercial, military and RP once fired cases, I kept 6 in case I needed them for reference, I mailed them to with instructions, 18 can be loaded and chambered with .005 head space, 18 can be loaded and chambered with .000 head space and 18 should not chamber and would need to be sized and the shoulder set back to chamber because the case from the head of the case to the shoulder was .004 (beyond a go-gage) to long, I did not have a chamber or case gage, I made one, I met him at the Market Hall Gun Show while setting with Don Wooldridge, by that time he claimed he had shot all of the cases at least 5 times, and he had to size and trim the long cases. I ask him if he saved a case from each group, he didn't.

Trouble with the die raising when sizing? worn out threads on the die and or press, collect on the warranty or do as I do, put the press in a bind, tighten the lock nut to take the slack between the threads and start sizing. If you believe the brass is sticking out purchase a feeler gage, perfect for measuring gaps when two pieces do not make contact, and relax, leave the press in a bind with the ram up, if brass compresses or flows give it time.

F. Guffey

[Unclenick]

Originally Posted by Bart B.

The RCBS Prec. Mic for rimless bottleneck cases should read zero when a GO headspace gage is in it and the thimble closed against it. . .

They missed on my .308 PM by about 2 thousandths. It reads about 2 thousandths over zero on a calibrated go gauge, which is why I assumed the case reading was their objective. I didn't check with them. That error is not a total surprise, I suppose. It depends whose gauges they use to do the setup and whether the operator has a good sense of touch for gauging?

You can't just assume headspace gauges are accurate, unfortunately. I once got a Forster .308 armorer's headspace gauge set and found some of them off by as much as 2 thousandths. I now use a Dave Manson gauge as my reference because I was able to validate it with a modified height gauge on a surface plate to be correct within half a thousandth (which was the limit of my setup's resolution). It is probably better. The RCBS mic did the comparisons to the Manson gauge and the Forster gauges and among the Forster gauges themselves. One gauge labeled, 1.638". was actually 1 thousandth shorter than the one labeled 1.637". You can't automatically believe measuring tools without calibrating or at least cross-checking checking them.

Originally Posted by Bart B.

A case whose headspace is shorter than actual chamber headspace will still be shorter than chamber headspace after it's fired. Typically 1 to 2 thousandths of an inch shorter with normal max loads. . .

That's about right for new brass, IME. As you are undoubtedly aware, when you neck size-only, with enough reloadings the cases eventually grow too tight to re-chamber and have to go through a cycle of full length resizing. If you full length resize cases with the shoulder set back only 2 thousandths to begin with, as I was discussing, they will get pretty close to chamber headspace size on firing at full pressure. It they maintained that 2 thousandths after extraction, then what happens to neck sized-only cases would not occur. I think you will find a case with a properly annealed neck and shoulder that starts out just 2 thousandths short of the chamber gauge length will wind up within a thousandth of reflecting real headspace most of the time. Still depends on the brass and load, of course.

[Bart B.]

Unclenick says:
They missed on my .308 PM by about 2 thousandths. It reads about 2 thousandths over zero on a calibrated go gauge, which is why I assumed the case reading was their objective.

Lots of folks report about the same errors. That's fine by me.

RCBS Prec. Mic's are primarily intended to check the difference between fired and resized cases. There's probably a couple thousandths spread across all headspace gages made for a given cartridge. Not a significant issue in my opinion.

[GuitarXM]

So did you guys ever encounter that...where the dummy bullet goes inside the chamber?

I guess i pushed it too hard lol
I don't think I'm ever using that dummy bullet ever again...I feel that I might have damaged my chamber....

I'm just gonna use a cleaning rod to measure OAL.

[Unclenick]

Originally Posted by Bart B.

RCBS Prec. Mic's are primarily intended to check the difference between fired and resized cases. . .

Yup! Exactly. Comparative measurements. And they seem to be quite good for that. I haven't found any indication the threads on mine have any longitudinal wobble, as you sometimes see in all-thread, so I suspect the threads were turned rather than die cut.

As to tolerances, for cases, as you say, 2 thousandths is about all you can hope for. I've resized military cases fired in my own gun that came out of the sizing die with up to 4 thousandths spread, head to shoulder. That was before I got on the 2 thousandths setback train. Now I aim for just 2 thousandths in the most compliant cases. For the more recalcitrant ones, I find letting the case sit in the die five seconds, pulling it out to rest for five more, then running it back in for another five will usually get me an additional 2 thousandths. I also usually turn it 180° before the second 5 second insertion, just in case an asymmetry is involved, but I've never proven that really makes a difference one way or the other. Just seems like easy insurance.

As to chambers, I've gone to the good quality gauges with the thought that someday I might actually want to be able to interchange neck-sized rounds. Never have, though. Mind you, this is on my own guns with which I can ensure the same reamer has cut both chambers on the same machine tools with the same lubricant and floating reamer holder. They come out quite identical that way, but only if the headspace matches. And, I suppose I could ensure that just using the same gauge in both. Still, I don't like the idea of coming up a couple thousandths short. That matches the chamber headspace to SAAMI case max, which might get you in trouble sometime.


GuitarXM.

I've stuck the RCBS PM "bullet" in throats more than once. The tension adjustment seems to be fairly touchy that way. The most "damage" that is likely to do is burnish the throat a little which might actually reduce fouling a tad? Don't sweat it. For myself, I gave up on that part of the PM kit when the Stoney Point tools came out that let you use the actual bullets you are loading. Hornady bought out Stoney Point and now sells that system as their Overall Gage. If you don't want to buy more tools, though, you can make the RCBS one work with patience.

[GuitarXM]

Its weird though..I get a completely different measurement with the plastic bullet when i put it in the chamber by hand...or if i attack it to the bolt and close it...

When you say throat you mean chamber right?

[a7mmnut]

I'm interested in seeing what measurement you get with fire formed cases (once fired). I once bought a lot of .300 Weatherby brass that just would not chamber in my M700 Rem. Even after full length sizing on my RCBS dies, the shoulder dimension was off by at least .004-.005". Those really long cases were still within spec., as Guffey reports. Fire forming with a light load solved the problem and saved a couple hundred pieces of high $$$ brass.

As for brass flow, you really only notice this when loading rimmed cartridges and trimming for length. After just a couple of uses, you'll have to turn the necks down. Belted cases will get really light just above the belt.



-7-

[Bart B.]

Seems there is a big spread in belted cases' head to shoulder length in both new cases and chambers. That may be part of the reason folks shooting the best scores in long range matches gave up on conventional full-length sizing their fired cases and just used new ones all the time. USA military teams gave away hundreds of once-fired .30-.338 and .300 Win. cases to brass-hopping civilians as a result.

And the case diameter immediately in front of the belt on these magnums never got sized back down in conventional full-length dies. It prevented consistant positioning of the sized case (full length or any form of neck only) and accuracy was impaired. A friend of mine (many time Nat'l champ) figured out back in the 1960's, a way to modify a full-length sizing die to reduce belted case body diameter back to new-case size all the way to the belt's front edge.

It's a conventional full length sizing die with the bottom cut off very square a bit above the belt clearance recess and its top cut off a ways below the body-shoulder junction. The inside edges were smoothed up which prevented shaving brass and allowed easy case entry into the die. This 'body only' die would be used before or after a regular die sized most of the fired case body and neck back down and set the shoulder back several thousandths from its fired position. Belted cases fired and resized using this two-die method shot as accurate as new ones. No more accuracy-robbing interference between the back of the case and chamber. Folks using properly using such a die in conjunction with standard full-length dies get 20 to 30 reloads per belted case in standard SAAMI chambers. The military teams didn't want to do this so they just used new cases all the time.

Now there's a company making one called a Belted Magmum Collet Resizing Die and can be seen at:

http://www.larrywillis.com/