Headspace question

[jason75979]

I recently had a local 'smith assemble a rifle for me with my chosen parts. The action is an FN SPR, the barrel a Shilen match grade stainless select blank which he turned and chambered in .308 for me.
I purchased 2 boxes of ammo to break it in and begin the process of tuning a load for the rifle with the spent brass. I've read before how one member is adamant about checking the length of an unfired round before firing to provide a "measurement" if you will, of the effect the chamber has upon the casing. Well, the measurements were all over the place. From 1.623 to 1.64 prior to firing checked with a Hornady headspace comparator gauge.
After the firing, the brass is, for the most part, shorter
But, all fall within .0005 of each other(1.624-1.6235(guessing at the .0005 as its halfway at least between the 3 and 4)).
My question is wouldn't the firing "stretch" the cases to form the chamber dimensions? And if too small(the chambers headspace) wouldn't there be indications of excessive pressure?

[steve4102]

My question is wouldn't the firing "stretch" the cases to form the chamber dimensions? And if too small(the chambers headspace) wouldn't there be indications of excessive pressure?

Yes, the case should stretch to fit the chamber, no, not if the smith cut the chamber to Min specs. Meaning no room to stretch, a good thing.

Will a small chamber have an affect on pressure, no not if it is in the chamber, yes, if it is in the throat.

[Ideal Tool]

Hello, jason. Don't forget, that brass also "stretches" or expands radially..this will have a tendency to slightly shorten a case.

[F. Guffey]

“I purchased 2 boxes of ammo to break it in and begin the process of tuning a load for the rifle with the spent brass. I've read before how one member is adamant about checking the length of an unfired round before firing to provide a "measurement" if you will, of the effect the chamber has upon the casing. Well, the measurements were all over the place. From 1.623 to 1.64 prior to firing checked with a Hornady headspace comparator gauge”

That had to be me, I do not use the Hornady case comparator, I make comparators, I make chamber gages and my Wilson case gages are precision case length gages. You measured the length of the cases in 2 boxes of new ammo and found the length of the cases varied from 1.623 to 1.640, and I ask, how did you get the bolt to close on the case that was .017 thousandths longer than the shortest case. And you said the case length after firing was 1.624-1.6235.

The effect the chamber had on the case when fired, and I said that also, I have purchased new ammo, I have measured 20 R-P 30/06 rounds of ammo from the same box and found .001 thousandths difference in length from the case head to its shoulder/datum.

And I said I could determine the effect the chamber will have on the case when fired by determining the length of the chamber first. New, over the counter, unfired, factory ammo should be minimum length or = full length sized cases.

According to your measurements you started with new/minimum length size cases, according to your measurements your cases did not stretch when fired, according to SAAMI your chamber is .004 thousandths longer than your minimum length size cases but according to you, you measured new ammo, you chambered a case that is longer than a field reject gage and chambered it without felt bolt closing.



“But, all fall within .0005 of each other(1.624-1.6235(guessing at the .0005 as its halfway at least between the 3 and 4)”

F. Guffey

[F. Guffey]

“I recently had a local 'smith assemble a rifle for me with my chosen parts. The action is an FN SPR, the barrel a Shilen match grade stainless select blank which he turned and chambered in .308 for me”

Had I cut your chamber I would thought the length of the chamber important enough I would have informed you the length of the chamber from the bolt face to the shoulder of the chamber, and I would have instructed you on sizing cases to fit by adjusting the die to prevent moving the shoulder back too far, and I would have formed one case you could use to check your gages with.

F. Guffey

[jason75979]

No excessive or even noticeable amount of extra force was needed to close the bolt. I can, if necessary, post a picture of the calipers and the reading since some are in disbelief.
I will contact the gunsmith and return the gun to have the chamber measured.

[Bart B.]

If that new ammo has case headspace measuring from 1.623 to 1.64 prior to firing checked with a Hornady headspace comparator gauge, I suspect it's bad ammo. That's assuming you measured correctly. SAAMI specs for .308 Win. case headspace is from 1.627" to 1.634" which is a 7 thousandths inch spread. Your measurements have a 17 thousandths spread.

I, too, wonder how you chambered one with 1.640" case headspace in a chamber that's supposed to be no longer in headspace than 1.634".

[F. Guffey]

“No excessive or even noticeable amount of extra force was needed to close the bolt. I can, if necessary, post a picture of the calipers and the reading since some are in disbelief.
I will contact the gunsmith and return the gun to have the chamber measured”

Jason, I make gages, it is not likely your smith has anything beyond a go-gage, no go-gage and or a field reject gage. I determine the the length of the chamber before installing the barrel, after installing, I verify the measurement, I do not assume unsupported case head or case head protrusion.

I purchases 4 Mauser rifles for $25.00 each, all were on their second (wore out) barrel, and I was told the rifles were suspect, I used one barrel to test all 4 receivers, with 4 bolts, 4 receivers and 1 barrel, the combined difference with any combination was .001 thousandths, all of that without a go-gage. The case head protrusion on the barrel was .110, the barrel was Belgium and chambered to 30 Gibbs.

I would suggest you take the 2 boxes of ammo with your HORNADY case comparator with the rifle, and if there is .017 thousandths difference between the longest and shortest case from the case head to the shoulder/datum the manufacturer needs to know, again, the long case should not have chambered, the other numbers posted before and after firing would indicate a chamber that is close in length to the case length, meaning with minimum length new ammo, when fired, increase in length from the head of the case to the shoulder .001 (+/-) very little.



F. Guffey

[F. Guffey]

“And if too small(the chambers headspace) wouldn't there be indications of excessive pressure? “


Yes, the case should stretch to fit the chamber, no, not if the smith cut the chamber to Min specs. Meaning no room to stretch, a good thing.

Will a small chamber have an affect on pressure, no not if it is in the chamber, yes, if it is in the throat.




Not an easy concept to grasp, Unclenick takes the time to introduces reloaders to sequences of events that happen after the trigger is pulled, instead of thousandths of an inch time is used as in milliseconds.

And I say time is a factor, as time applies to Jason’s question, a case that does not fill the chamber must expand before pressure builds, if the case fits, is formed and fills the chamber before firing time is not wasted on case expansion. I formed cases for a wildcat, I used a heavy bullet and too much powder, friends informed me “that is some risky stuff”, the bullet and powder combination was the maximum load for that chamber after the cases were formed, but because of the case expansion when forming the bullet was out of the case and traveling down the barrel before pressure was high enough to cause concern, as opposed to the same load after forming the cases, the form case does not expand to the chamber, time is reduced, pressure climbs before the bullet gets started down the barrel. My fire forming load was the maximum load with formed cases. The shoulder of the formed cases was formed .202 ahead of the parent case, the diameter of the case body was increased and the shoulder angle went from 17 degree 30 minutes to 27 Degree. And I was told I was forgiven for a big mistake.

So, yes, the size of the chamber does effect pressure, when keeping up with many factors at the same time “wouldn't there be indications of excessive pressure” I would say an increase in pressure when the case and chamber has little room for air room between the case and chamber, not necessary excessive high pressure, but time is a factor, reducing room for air between the case and chamber increases pressure.

I am the fan of cutting down on all that case travel, I want my case to fit the chamber from the bolt face to the shoulder, I do not insist the case body fill the chamber.

F. Guffey

[Gunplummer]

Factory brass sometimes has a much bigger radius at the shoulder and neck area, which will give false readings.

[jason75979]

Evidently I imagined the 1.64 measurement but here is a sampling of a couple of 10 remaining.
Testing method: placed bullet in comparator head and closed jaws, slowly spun cartridge so to help centering and arrived at measurement. These are unfired cartridges.
Zeroed
Low end
High end

[PA-Joe]

This is an example of why in reloading you can make better rounds than the factory. Their rounds may come from different dies and machines.

[F. Guffey]

Jason, the spread of difference between case lengths from the shoulder/datum could indicate the lack of quality control at one manufacturer of new ammo, I can not find where you have listed the manufacturer of the two boxes of ammo, most of the new unfired ammo I have checked came from someone with a problem.

A shooter with 2 boxes of R-P ammo and a new rifle had 5 fail to fire out of the first box, the 5 failed to fire rounds were chambered in two other 30/06 rifles and hit with an additional 4 strikes of a firing pin, nothing, conclusion? Bad ammo, a reloader/shooter at the range called me and ask if I was aware of R-P ammo having bad primers etc.. And I always have to ask “WHY!!! ? Long story, I instructed them to call Remington, and I told them where to find the phone number, my thinking? Remington would like to know.

later that day the reloader/shooter at the range calls and says he is bringing the 15 fired cases over with the 5 that failed to fire, and again everyone at the range left there saying “BAD AMMO”, he left the green Remington box in the litter can and did not get the contact information for the proud but disappointed owner of the new rifle and ammo. First I collected the tools for measuring, weighing, and pulling apart, the fired cases chambered in my chamber gage with thumb pressure, the protrusion was .092 thousandths, (in my opinion the fired cases were fired in one very fine chamber). then we checked the failed to fire case lengths, in the chamber gage the case protruded .090 thousandths, in a perfect go-gage length chamber the case would be .005 thousandths shorter than the chamber.

After pulling the bullets we weighed the bullet, powder and case, in my opinion the results was better and or as good as can be accomplished at home, then we punched the primers out of the FTF cases, examined them and then reinstalled them back into the same cases they were removed from, we chambered them in one of my M1917 rifles and pulled the trigger, with out bullet and or powder, the firing pin crushed the primers and all 5 failed to fire fired in the M1917. My reloader/shooting friend then went home, got on the Internet, did searches and then called me wanting to know where I purchased the tools used to check the cases. the answer, the RCBS 10/10 is from RCBS, the Wilson case gage is from L.E. Wilson etc.. of course, he was not asking about the obvious, the other tools were tools that had/have more than one purpose and disguised as tools used for reloading.

Again, a builder, collector, recourse 1911, Garand, and anything 03 to 03A4, shooter reloader was building a period correct Rock Island 03 for 1911, he had a box of go-gages, nothing In the box gave him the length of the chamber in thousandths, he had given up on help from the Internet. As soon as someone would say “You can.....” the next response would be “No you can’t......” anyhow, I was purchasing a mill from him and gathering the parts, when finished I explained to him “This is your lucky day......” I explained to him I check head space 3 different ways without a head space gage, I collect parts of tools, tools and other gages from the wall, bench and tool boxes in his shop and started, his new creation had a chamber that was .0075 longer than a minimum length/full length sized case. He had no less than 80 Springfield 03 and 03A3 bolts, not one bolt of the 80 would reduce head space .001 thousandths, I have no less than 30 (most new old) Springfield bolts, I offered to check my bolts knowing I could not reduce his head space with one of my bolts ‘PLUS’ he had one straight handle 03 bolt, that one was in the rifle, and I have one straight handle 03 bolt, it is in a Rock Island 03, ground to fit a scope. A bent 03 bolt would not be period correct for the Rock Island.

Then I offered to form cases for his new creation that would off set the difference between the length of the chamber and the length of his cases, he has the only hydraulic operated press I know of, it has a two way piston, and no, the piston is not an add-on.

Again, I want to know the length of the chamber, I want to know the length of the case from the head of the case to its shoulder in thousandths, the head space gage be it a go, no or beyond gage, the gage is a fixed length gage, I can modify a go-gage to check the length of a chamber in thousandths from .005 longer than a minimum length case to infinity, problem, it would no longer be period correct and it would have less less value.

F. Guffey

[jason75979]

Suprisingly enough, factory Lapua Silver Scenars 167 grain.
They shot really well though. This was my last 5 shot group from a clean bore.picture is rotated 90 deg. counter clockwise.

[F. Guffey]

“factory Lapua Silver Scenars” Information belong with your first post, but then you had “I purchased 2 boxes of ammo to break it in and begin the process of tuning a load for the rifle with the spent brass”

My opinion, it is not going to be easy to improve on your results with reloads, it goes back to the discussion/rational for or against full length sizing, some fantastic groups have been shot with factory ammo, do not want to bore anyone but I paid $120.00, $150 and $250.00 for three rifles that shoot one hole groups with factory ammo, the best results come with Federal GMM, then there is R-P in the green box, the $120.00 (Remington M1917) and $150.00 (Santa Fe Remington 03 before A3) were purchased for parts. Then there was the Mauser 98 late issue, the rifle was dipped in something black and the stock appeared to be stained with red shoe polish, without a scope, I thought the bullets were tumbling, another ugly rifle I added to the leaver policy group, I ‘lefter’ the way I founder.

Thanks for hanging in there.

[edward5759]

When I did .308 and 30-06 chambers I would use a pull through reamer. This was a standard for many years.
I never found that measuring factory datum points were accurate.

[Unclenick]

jason75979,

Note that the 0.400 hole in the Hornady comparator has a slightly radiused mouth. This makes it read below actual numbers by a few thousandths. You have to get a good quality headspace gauge (Dave Manson, Clymer, Pacific, JGS; not Forster or other cheaper ones) to calibrate it with if you really want to learn absolute numbers. However, that's likely a waste of money from a practical standpoint. Relative numbers are normally all you need for setting up loading dies, tracking bolt lug setback, etc. As Mr. Guffey has emphasized, it is really a matter of the ammo fitting the chamber and not what SAAMI or anyone else thinks it should be. So relative numbers are just fine.

I am going to hazard a guess than when your Hornady LNL gauge reads 1.623", a good grade headspace gauge would read 1.624" or 1.625". In other words, you're getting numbers about 0.005"-0.006" below absolute. That's about how much error my copy of that gauge gives me. Figure that when you fire a round, you get 0.001" to 0.002" elastic rebound in a new case, so I suspect your chamber is just about dead on the minimum 1.630" dimension, and the reason the cases come out of the chamber the same size they went in is that rebound.

If you fired at a higher peak pressure you'd have less rebound. If you resize only the necks of your cases (just don't run them into the sizing die far enough to start squeezing the sides of the case) and reload and fire them, measuring the case shoulders each time, you'll find they gradually grow that extra one or two thousandths. Eventually, with enough firings (perhaps a half dozen; it depends how warm you load), the cases will form snuggly enough to the chamber that you start to feel light resistance closing the bolt on one. At that point your actual headspace, less gauge error, was probably reflected by the previous measurement pretty closely. That's the useful number for you to record as your reference headspace.

For break-in, Varmint Al says he likes to put some Flitz on a patch and run about 50 strokes in a new barrel (using a bore guide, I presume), then calls it broken in. That tends to clear whatever burrs or sharp edges might remain from manufacturing and lapping that encourage excess fouling. If he gets a tough dog bore (some are for no obvious reason) that fouls excessively, he repeats with JB Bore Compound (I prefer Iosso Bore Cleaner for this) to polish a little more deeply. None of this kind of polishing comes close to removing enough metal to affect the bore tolerances within the normal life expectancy of a bore. It's in the low millionths of an inch at most, and too small for a micrometer to measure. It sure saves the expense and the wear and tear on your throat from firing "break-in" shots, though.

When it comes to load development, there are lots of ideas about how best to tackle it. I always suggest reading Dan Newberry's site for a starting point.

[F. Guffey]

“the barrel, a Shilen match grade stainless select blank”

http://www.shilen.com/barrelGrades.html

Unclenick, the link to Shilien list his barrel as lapped, had the barrel been chrome-moly Shilien would polish it for an additional charge.

“factory Lapua Silver Scenars” If I purchased Lapua it would be for all the reasons listed by reloaders, they measure it, they weigh it, they check it for capacity, if the Lapua case length was off more than .001 thousandths from the head of the case to its shoulder, Lapua would never hear the last of it, and every time a reloader started listing it as the very best cases/ammo on the market, same thing, I can beat varying case length with almost anything I purchase.

F. Guffey

[Unclenick]

Yes, they are lapped, but I think the folks who first came up with the concept of break-in were benchrest shooters with lapped barrels. Gail McMillan always insisted it was a waste of good barrel life, but I did an experiment while firelapping an old military barrel that suggests that's not 100% the case. As the abrasive-loaded bullets I shot through that barrel became finer than normal lapping abrasive (400, 800, and 1200 grit), I stopped after each set of lapping bullets and cleaned thoroughly then fired ten regular jacketed bullets. I then counted the number of patches of it took to clear the last trace of copper. As the abrasives got finer and finer and the bore was more and more polished, the patch count kept getting lower and lower. So there does seem to be some cleaning advantage to further surface polishing than the as-lapped bore usually has. I think that's what Varmint Al has found, except that, unlike my firelapping (which I would not do to a hand lapped bore), he feels the Flitz usually does well enough to achieve that same result in a lapped bore.

On the other side of the coin, I've seen the argument made that if you over-polish a barrel it can take longer to settle because the carbon fouling doesn't reach accumulation equilibrium as quickly. The old rule of thumb was that if you changed powders in the middle of a match it would take 10 rounds for the fouling to re-equilibrate to give best performance consistency. The over-polished theory suggests that would take longer with a really smooth bore. I have not proved this idea in anything I shoot, but I'm not shooting benchrest guns. I note that G. David Tubb's Final Finish system leaves a highly polished bore and he's found that polish an advantage in non-BR match shooting.

One thing that didn't pop into my head right away regarding this whole thread is that the Lapua Scenar Silver bullets are moly-coated. I would not use a coated bullet for break-in. If you subscribe to the idea that break-in will burnish the surface, you want the greater friction of an uncoated bullet for the task. Otherwise it will take more rounds to do the job; maybe many more. You also want to avoid having moly pack the microscopic surface imperfections you are trying to burnish over, as that might actually interfere with burnishing. Boretech makes the best moly removing cleaner I've tried, and I would suggest cleaning with that to remove moly, then using either their Eliminator or their C++ product or KG-12 to clear copper traces, then break in with jacketed bullets. The cheapest commercial ammo you can get should be fine for the task. I would use a light bullet load as the heavier ones often don't bump up to fill the corners of the lands as well.

Howa's U.S. distributor recommends using Windex to clean any traces of hydrocarbons from the bore before firing each additional break-in shot. They offer the theory that you should fire ten rounds with cleaning like that between each shot and also five minutes cooling between those shots. They claim that causes the barrel to tend to take a set in the cold bore position, so that it won't tend to walk as it heats up in later firing. Their procedure is here. I don't have proof they are right about this, but ten shots is a pretty tame quantity to invest. They claim most of the copper wash fouling has stopped being left in the bore after round 6 or 7 by this method. They then go on to fire another ten in pairs between cleanings. I've never understood that idea. I'd clean between each break-in shot to better expose the bore to the burnishing. But they also say that is just insurance that burnishing is complete. They seem to think they were really done at 6 or 7, if I am reading them correctly.

[old roper]

Originally Posted by old roper

The OP is talking about custom barrel and most like Kreiger/Bartlein etc will not warranty any lapping of their barrels.

No doubt that's true. Once you start modifying any firearm or component to improve accuracy you risk that. Most of us do it anyway, but it should be done with full understanding that you are most likely putting yourself on your own once you undertake to do it. Some of the gun makers don't void the warranty, but will put any changes you made back to factory spec before returning the gun to you, should you send it in for some reason.

[jason75979]

Originally Posted by old roper

The OP is talking about custom barrel and most like Kreiger/Bartlein etc will not warranty any lapping of their barrels.

http://www.bartleinbarrels.com/whoarewe.htm

I sure hope they don't begin a recall due to that group I posted. I WAS somewhat proud of it.
A lot of good info here.
Thanks gentlemen.