Headspace Variance

jackie schmidt said:
Jerry, of all of the methods we use to determine such things as 'shoulder bump' and the like, the feel method is the least desireable. It is a good way to creat exccessive headspace. In fact, I advice all shooters to NOT use this method, as there are other factors that can render "false readings". Measuring with a suitable tool is the only accurate way to determine these criticle measurements.....jackie
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Jackie, several of the HOF shooters I know use the feel method.

In the benchrest application only, with a properly matched sizing die and a clean chamber what is there for the case to hang on to give a false reading???
Please explain.
 
Jackie,

the failure will usually occur at the point just forward of the solid web because that is where the maximum pressure is
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You may be right, but I've always assumed the pressure in a chamber is even. Are you sure of this?

But I'd agree that anyone who finds the brass thinner just above the web is not correctly sizing their cases. It sure isn't thinner there with virgin brass.

If you are fireforming cases, the surest way I know to get even cases is to lightly lube the cases befreo fireforming. You still need at least 45,000 psi, but I'd skip the 65,000+ psi loads for fireforming with lubed cases. I use a water-soluable lube so the chamber can easily be flushed out, but in a pinch, even WD-40 will work. Just swab the chamber out with alcohol when done.

Having said all that, the original question *probably* results from a measurement problem.
 
Jerry

Regardless of how many HOF Shooters use the "feel" method, it is not being responsible for us to advocate a method of arriving at such criticle dimensions by what amounts to guess work.
I repeat. The correct way to do this is accurate measuring, with the proper tools.........jackie
 
Jackie, how can using a dial caliper and a barrel shoulder tool be more accurate than the actual fit of the cartridge in the actual chamber?? How can this actual fit be guesswork??

This type measurement using a dial caliper is liken to the argument of using a dial caliper to measure neck wall thickness when the actual measurement that counts in loaded round neck diameter is the measurement over the seated bullet.
 
Jerry

For seasoned shooters who are aware of all of the variables that can be involved in making a case have "feel", or not, this might not be a big thing.
But, keep in mind that we have multitudes of shooters who log onto this site,looking for methods that are correct, and fool proof. I say again, it is our responsibility to give them the correct way to arrive at these measurements.
Since you brought up HOF Shooters, here is what the best of them all told us.
Tony said that when students come to his school, one of the first things he discovers when anylizing their loading procedures is that most are bumping their cases shoulders back way too far, because they were using the "feel" method. Like many of us, he believes that the only true way to arrive at these criticle dimensions is to actually measure the amount of shoulder set-back.
One of my good friends, who attended Tony's School, found that he was actually bumping his shoulders back over .008 each time,because he was using the "feel" method. He was simply ignorant of the variables involved.
Jerry,I am not ging to argue this point. You, as a Master Craftsman, know that actual measurements taken with the proper tools are the only fool proof, and correct way, to do this.........jackie
 
Jerry

Yes, we all subscribe to the "feel" method but if you are blindly bumping the shoulder waiting on that "feeling" you may end up with a case separation. When you have bumped the shoulder 3 or 4 thou and the case remains tight you have to abandon the feel method and dig out a different sizing die.

Thing is, if you end up measuring base to shoulder...why not just start there.
 
Oh good grief Jackie and Wilbur, I guess I'll reluctantly concede on this argument!! (I'll still use the feel method for myself though since I know my dies and I know my chambers)
 
Jerry,
I challenged a good friend who had been very resistant to using a gage and calipers to set his FL die multiple times by feel, saving a sized case from each setting to be measured. After he saw hat he was all over the place on headspace, he made some gages. The feel method requires is a die that is correct for the chamber in question; many are not, and their owners clueless about the need to determine if it is, and how to do so. On the internet, we speak to the world.
 
Boyd Allen said:
Jerry,
I challenged a good friend who had been very resistant to using a gage and calipers to set his FL die multiple times by feel, saving a sized case from each setting to be measured. After he saw hat he was all over the place on headspace, he made some gages. The feel method requires is a die that is correct for the chamber in question; many are not, and their owners clueless about the need to determine if it is, and how to do so. On the internet, we speak to the world.
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Lets look at the basics the ordinary and occasional handloader has. They have a reloading manual. The Hornady manual says to set the ram all the way to the top and screw the sizing die down to bump the shell holder. What if the shell holder is brand A and the die is Brand B?

The Sierra manual says, for non rimmed cases, "if the die is out of adjustment and sizes these cases improperly, the cases will not seat properly in the chamber, proper adjustment of the die is important"! For rimmed cases, let the rim control headspace. Ridiculous!

The Nosler manual, under Full Length Resizing says," the entire surface of the case, including the shoulder, is set back to APPROXIMATE original dimensions of the factory case"! This is precision??

Need I go on through Lyman, Barnes, Speer, etc??

Boyd, I'll agree that using a barrel shoulder tool made by the same chambering reamer as that chamber may be more accurate than the feel method would be for someone that is inexperienced in gaging and especially if they are using a "spring-loaded" not stripped bolt. How many of these occasional reloaders shooting factory guns are going to have such a tool as the barrel shoulder tool??

But on the other side of accurate headspace gaging, that same someone, using a single contact point gage like the Hornady LNL (Stony Point-Whitetail) gage and a cheap set of dial calipers will get a no better measurement that doing the spring-loaded bolt method.
 
I've seen handloads where the headspace was measured exactly (or even a bit short), and you could still feel the case as it chambered using a completely stripped bolt asm. This showed that there was another surface on the case coming into contact with the chamber. This is fairly common with the longer tapered calibers, when custom chambers are made to extremely tight tolerences. Most good machinists are aware that a very slight taper can be very difficult to measure, especially a shallow angle like the body of a case. The taper on the resizing die also needs to be perfectly cut.

I believe in measuring headspace accurately and knowing exactly where it is - for sure. Then verify the fit with the feel method, because this can reveal other problems. I once had a custom 308 Win chamber that actually headspaced on the body taper of the case. Accurate measuring was the only way to discover this problem. The symptom was occasional difficult extraction, because the handloads were actually being press fitted into the chamber (just like using a morse tapered chuck).

- Innovative
 
rem6mmbr said:
I measured my fired cases with a Hornady headspace guage and found that my headspace varies by 0.003. The cases have been fired 3 times. I'm new to BR, but I assume that this variance can't be helping accuracy. My question are: Why do I have this variance, what do I need to do to reduce it and what is the normal variance, if any. Thanks.
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the seasoned br shooters that have responded to your question "KNOW' that they are really talking about case size and not chamber headspace.

not knowing how new you are, you should understand that HEADSPACE is a characteristic of a chamber, not the brass that comes out or goes in. what you are measureing is headspace CLEARANCE. if there was zero clearance you would definitely feel the bolt close, less than zero, force it closed, and more than zero, should close easily.

as has been pointed out the spent primer should be removed for measurement of the case. technique is important.
i believe most br shooters size to about .0005/.0010 less than headspace. some size even more, going for bullet in the lands and base of case in the bolt.

what kind of brass, what kind of prep was done? all the loads the same, same temp? this is a small variation on the "after" product, what did the "before" product measure ?

mike in co
 
mike

You are correct, we toss that term "headspace" around, when what we are really talking about is the distance between the bolt face and the face of the case when the case is chambered and the bolt closed. To Benchrest Shooters, that is the dimension we are interested in, (I suppose), which most of us agree is around .110 to .002 inch.........jackie
 
I use the term "headspace" because most non-benchrest shooters (or new benchrest shooters) are familiar with what it means without going into a long explanation. However, you are 100% correct that it is more accurately described as the distance between the bolt face and the face of the case when the case is chambered and the bolt closed.

- Innovative
 
jackie schmidt said:
You are correct, we toss that term "headspace" around, when what we are really talking about is the distance between the bolt face and the face of the case when the case is chambered and the bolt closed. To Benchrest Shooters, that is the dimension we are interested in, (I suppose), which most of us agree is around .110 to .002 inch.........jackie
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jackie...thats got to be a typo ??? .110 ?

mike in co
 
Boyd asked about the load, and I've seen that come into play with headspacing. It's like the barrel steel(about the chamber) yields a bit differently at a certain point, and of course springs back. The brass does the same thing, but differently than the barrel, and can be left binding in the chamber. It seems to me that moderate and consistent loads help with consistent headspacing, as well as annealing(actually, stress relieving) now & then.

I have to bump cases everytime after the second or third fireforming, and use gizzys cut with my reamers. At this early point, I go by feel as mentioned, bumping .0005 at a time, to determine my desired final headspace measurements(ever so slight bolt turn resistance). This is with moderate loads, and I'm careful to see that ONLY the shoulders are sized at this point, and that my measurements makes sense per the reamer print. From then on, this is my goal -as measured-
I use dies made by JLC Precision with my reamers, for bumping/sizing.
With this and my loads, I get little FL sizing, and have never needed more.

But by ~15-20 reloads the bumps 'take' less. The die(or shellholder) has to be adjusted, sometimes from case to case. The headspacing only holds for that day. By morning the next, bolt closure would be difficult with a few of the cases, and measurements show it. Time to anneal(many would do so earlier, or bring in a new batch of cases for that barrel)..

You make it sound like your brass had been consistant until the third fireforming brought out differences. So I wonder about your load, and annealing.
Are you in load developement with these firings?
Have you measured HS right after bumping, and then let the brass sit for a day & then re-measure?
 
mike in co


My guess is this


001 got turned into 110


simple dyslexic slip of the fingers...I do it allatime :)


al


BTW I disagree with Jackie on this one. .002 is 'WAYYY to much! .002 times 10 reloads is more than 10 thou in case stretch.....20 reloads and you're into trouble. But then Jackie throws out his brass before it could become a problem. I think keeping it just under .001 is better, I can go a half a thou and still chamber a round after the brass has sat a month. Less than half a thou and you're dealing with creep and temp changes.
 
Guys, until rem6mmbr comes back and describes his situation we can only assume he/she is the greater group of Sportshootin' Sams with his Savage Sevenhundred Supersniper. And if he is just that, nothing wrong with being so, then he is at the mercy of various reloading manuals that The Grinning Gunslingers Gunshop sells. He must hope that the cartridge and gun manufacturers know about SAAMI specifications.

In the world of SAAMI, there are terms like maximum cartridge dimensions and minimum chamber dimensions. As long as maximum cartridge does not exceed minimum chamber he is in business. If, in the SAAMI case, even if minimum cartridge is not exceeded and even if maximum chamber is not exceeded he is still in the shooting business.

Until we know more, expressing how we do our benchrest thing doesn't hurt either, I guess.
 
Jerry: I don't know if I would classify myself as a "Sharpshooter Sam", but I have on many occasions refered to myself as a gopher shooter. I appreciate the humor, it made me smile. My apologies for coming back into the thread so late, it's just that there where so many knowledgable responses that I was learning alot just reading. I've learned that sometimes a person can learn more by keeping his mouth shut.

Perhaps I should have explained "new" as meaning my next match will be my first. I've shot competition blackpowder for years and in general have been competing against myself in centerfire for over 30 years. You can only have so much fun by yourself, besides. I decided to go to a BR match as a spectator and got hooked (I think). Prior, I was having a rifle built as an accurate coyote gun. It had a Krieger #17 HV barrel chambered in 6mmbr with a PTG reamer. It has a 0.271 neck, 0.040 freebore, 30 deg. leade and the Rem. 700 action is "trued".

After the match, the rifle morphed. I replaced the J-lock firing pin ass'y, added a single shot follower, and skim bedded the works into a McMillan stock. The weight is about 12.5 lbs. Now, I know this rig can't compete with a high perforance PPC. I was just using what I had, with upgrades, to see if BR really is my bag. If I like it I can still learn alot by being on the range with real BR shooters and get a PPC later. If I don't care for it, well, I've got a hell of a coyote gun. My last 10 groups combined agg'ed at 0.325". I was told that flags would be helpful. I ordered some, but have never shot over flags before. The folks at the BR range said that they would give me all the help I wanted. They said that no matter how good a shooter a person may be, they all started exactly where I am. Nice down to earth people at this range.

That said, thank you to everyone that replied. I wasn't stiffing the thread, just sitting back, reading and absorbing.
 
Oops

That is supposed to be .001. And just think, I actually proof read my post.
Al, would it surprise you that with the loads I shoot in my 6PPC Competition Rifles, I sometimes bump the shoulder as much as .002. I do this as the cases tend to get a little stretchy toward the end of the agg. Seems to have no ill affects at all.
Of course, everybody does what they think helps them shoot better aggs in Matches. I am sure you have noticed that I do a few things that tend to go against the general accepted rules regarding Benchrest.........jackie
 
The reason that I asked about your load has to do with the way that a case comes to its greatest possible base to shoulder length (in a given chamber). At moderate pressures a case may not fully stretch back to the bolt face. One way to see this is to trap a fired case between the jaws of a caliper, so that one jaw runs across the diameter of the head, and hold it up to a light source, to better see if there is a slight gap on either side of the primer. If brass is loaded to a pressure that is right on the edge of causing the primers to be flush with the head, normal brass and pressure variations may cause what you are seeing. I would guess that if you loaded some of the same cases to the highest safe level of pressure, the "headspace" variations that you wrote of would disappear.
 
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