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Posted: 4/8/2008 1:04:53 PM EDT
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So I've always noticed my 6.8 spits out brass really dirty like. I put it shiny and after I fire it its really dirty. Someone told me this could be due to bad headspacing. Any validity to this I'm shooting a 6.8 |
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It could be an excessive headspace issue but it's easy to check so why not be sure so you don't have to guess? Depends on what ammo you are shooting also. Some ammo is made so out of spec. that it will damn near fire in anything. Only thing you can do is switch ammo and try to get some with a headspace that more closely matches your chamber. If your reloading, you should already know what your headspace is and thus bumping your shoulder back the correct amount. Dale McClure |
Huh? Not one thing you have stated is correct. Where to begin? Headspace is a chamber issue, not ammo. Go from there. |
Thank you for proving my point. The head of the case is in contact with the bolt, not the chamber, ei headspace. The cartridge body, shoulder and neck are in contact with the chamber. Ammunition is made to minimum SAAMI specs so it will work and be safe in the shittiest chambered rifle. When the SAAMI people first released the specs of the 6.8 SPC they transposed two sets of numbers which had the rifle mfgs making the chambers smaller and the ammo maker producing ammo a bit larger. Early issues with the 6.8 SPC have been with tight chambers and throats that have caused excessive pressure. It has since been corrected. Granted the chamber can be reamed too deep which will cause headspace issues, but ammo selection will not solve the problem. I would recommend that the OP gets a set of headspace gauges to confirm if that is the issue. |
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And so you are busting my balls for what? The neck of the brass and the clearance to the neck of the chamber creates the headspace. You are talking about where it is measured, I am talking about where it is created. Everyone should know what headspace is, (most don't) but they should also know how and where it is created. You are talking about the exact same thing I was. You just didn't get any last night or something and looking for an argument. You have contributed nothing to the original posters question. And your stupid insinuation that no one who reloads should know the headspace of the ammo they are loading. That is just plain ignorant and stupid on your part. FOAD |
It appears that you are the one who did not get any last night as you are the one who wants to start an argument. The neck of the brass does not cause headspace issues. You can easily trim the neck back. You can easily bump the shoulder back. What you can not do is mess with the head of the case. Headspace issues are a result of the case head not being in contact with the bolt face when the firearm is in battery. The neck of the case has nothing to do with it. If the neck of the cartridge is too long, the should will not hit the chamber and the bolt will not close. If the neck is too short, the shoulder of the case will be in contact with the chamber, the bolt will close, but there will not be a tight seal in the throat area which will allow gas to leak. |
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I admit I made a mistake in the last post using the word neck instead of shoulder. Headspace is created betweeen the shoulder of the brass to the shoulder of the chamber. My first post was correct. It was only until you decided to step in a pile of your own crap when I used the term "neck". And of course you are still correct that headspace should not be measured, so why argue about it? Huh? |
You've really sunk this thread in so many ways. Not only your lack of knowledgeable use of terminology and apparent ignorance of the development of the 6.8 SPC, you top it off with personal attacks. Ammo will not solve the problem as you suggested. The chamber is not a constant as you also mentioned becuase there are 2 specs now for the 6.8 SPC. Plus chamber reamers wear over time and if the mfg does nothing to rectifiy the problem, things get fubar. I could continue, but your retort would only mention of "crap". |
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Let me be clear:Proper headspace can be measured and adjusted in the same caliber no matter what chamber, or brass. This is true of the 6.8 whatever unless it is a belted case. If you don't even check headspace then how the hell do you even know what you are talking about? I check and set headspace on every caliber I shoot except .22 LR. Maybe setting headspace and winning has something in common. You think? |
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Head space is the distance from the bolt face to a datum line on the case shoulder when we are speaking of a rimless bottleneck cartridge. The word "headspace" is the name of that distance. I say that because when that measure is wrong on the large side people call it "excessive headspace" and that's not exactly the right term for that. I have still seen cartridges that were fired in incorrect larger then headspace specification chambers still make a seal (obturate) with the chamber and not be blackened. Another cause to blacken a case is that it didn't obturate to the chamber wall (esp the neck portion) because either it was too low of a pressure round or the case necks were extremely hard. Most the time AR's don't have brass come out fired looking super shiney to start with. But if your's are really blackened then something is wrong. If the headspace is too long I would think the primer would be really really flattened like in very high pressure. Being the extractor will hold the case against the bolt face and let the firing pin fire it the case would expand to fill the chamber. Have you set a fired case along side an unfired one and see if where the body meets the shoulder is longer then the one not fired? The headspace gauges would be thing to have to check that. You can use shims on the bolt face to check headspace if you know that the headspace and maximum headspace are supposed to be. |
Correct, proper headspace can be measured, by the use of headspace gauges which I mentioned. Did you? Headspace is use to measure the minimum and maximum allowances of chamber dimensions based upon SAAMI specs. How do you set headspace on an AR15 barrel? A Remington barrel? Those headspaces are fixed to the dimensions of the boltface as the barrels are static. Unless you use a different bolt in the carrier or bolt body in the Remington or even take more drastic measures the headspace is set . Something has to change. How do you change headspace. Brass is not the issue with headspace, so leave it alone. |
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And so if I quit checking and setting my headspace will I keep winning? I only shoot .223 in bolt guns and yes, I always check and set headspace everytime I reload for a match. And I win. I check headspace between each relay on my 6PPC while reloading between each target at the range. So do my competitors. If I quit that headspace step between targets will I still win? I doubt it. Headspace is all about the brass fitting the chamber and not fitting the chamber to the brass. Headspace is measured off the datum line on the shoulder of the brass. Headspace is adjusted by bumping the shoulder back as necessary. I''m glad I didn't learn to reload for competition from you. In fact, I learned from two fellas who are "Hall of Famers" in NBRSA. The most accurate rifles and shooters in the world. Dale McClure |
Headspace is set on an AR15 barrel when the barrel extension is screwed on, then it's pinned and the pin serves two purposes..it pins that extension and it indexes the barrel, that is so the gas port is straight up at the 12 o'clock position. On a Remington bolt gun the gunsmith will have the barrel all threaded and the threaded portion the correct length to place it in the correct position in the receiver. It will have a partially chambered chamber. Then screw the barrel into the receiver and using headspace gauges and a finish reamer, ream it to it's final correct headspace. On Savages with the barrel nut the barrels are fully chambered. Then they screw the barrel into the receiver with the bolt in the receiver and the correct headspace gauge and screw the barrel down until it is just the right snugness against the gauge and then torque the barrel nut down. |
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ProjectNick, Hey, What ammo are you using? What make and model is it? How long have you had it? Brand New? How many rounds? While sometimes ARs can have improper headspacing, 99.9% of the time they are correct. But there is a chance yours could be off. It could be becasue of the bolt and hopefully that is the issue as its the easiest to fix. Get another bolt. Unless its from Kotonics or another smaller shop I would say checking headspace on your own first rather then sending it in will help you not being without your AR for extended time as you just now have gotten out and started shooting this year. First thing I would do is try some other ammo and see if you still have the same issue. If not then it could be defective ammo. If the other ammo is fine contact the manf of the problem ammo and get replacement sent. If its SSA I would call and speak to them and tell them your issue. If it still has the same issue you will need to check your headspace on the chamber which you now probably know much more then you thought you would about it.  You only need to get a No-go gauge for this issue as the problem would have to be excessive headspace, but I would get both as they are good to have and will allow you to check your new bolt both ways. You might as well check both but start with the no go as its the most likely offender. To measure headspace with these gauges, first strip and clean your rifle. Chamber and bolt must be squeaky-clean. Then disassemble the bolt. Now slide the No-Go gauge in place. Attempt to gently close the bolt. You should not be able to do so. Do not try to force the bolt--use only fingertip pressure. You might be able to catch the leading edge of the locking lugs under the shoulders of the barrel extension. If you had not removed the ejector, you could not feel the resistance, as the force needed to overcome the ejector spring would be too great for the delicate feel needed. DONOT FORCE IT!! If the bolt closes on a No-Go gauge, you'll need to replace the bolt first. If after getting a new bolt it still is closing on it you will need to send your rifle in and they will need to replace the barrel. If you do this on your bolt and it doesn't close then you do not have excessive headspace and that isn't the problem. SO you should check the minimum headspace just to be sure. Slide the Go gauge into the chamber, and gently close the bolt. Since the AR-15 is a multi-lugged bolt you should be able to turn the bolt by hand without resistance against the locking lugs. If there is resistance, or the bolt handle stops before it is completely closed, headspace is under minimum dimensions and must be opened up. For that you'll need a finish chambering reamer. If this is chrome lined barrel it could point to improper chrome lining and I would send it back and have them replace the barrel becasue to extend the chamber they are going to be removing some of the CL when they ream it out. First try different ammo. Do the cheapest and simplest first and work your way out. Hope this helps and I didn't make it sound to confusing it si really fairly straight forward once you get into it. |
Its a Kotonics barrel from the first batch that ever sold. You know the ones Tim called "Sub-Par". I'm also shooting reloads, I'm still considered a beginner reloader, because I got into reloading as a result of buying the 6.8. I'm going to buy a no-go gauge I guess and see what happens |
You could use shims....say like paper. Mic them so you know how thick the paper is. Keep placing more on the face of the bolt and see when it won't close fully anymore and then tell us here and I'm sure someone would know by the accumulated figures if there is too much headspace. It's easier if you remove the ejector, maybe even the extractor. If you're using a live round either make a dummy one or remove your firing pin. You can just use finger pressure to shove the bolt carrier group forward and if you remove the extractor you can push it all back out with a cleaning rod. Save you buying a gauge, but a gauge is good to have anyways. Just thought you'd want a quicker answer to whether you headspace is too much. |
| If the ejected case is covered with soot, it indicates the case neck is not sealing against the chamber neck. This can be caused by very underpowered loads that don't create enough pressure to expand the case neck against the chamber. Or it can be caused by an oversize/irregular chamber neck. |
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The amount of misinformation about "headspace" in this thread is troubling. Headspace is the mismatch between chamber dimensions and cartridge dimensions. Chamber dimensions alone do not determine "headspace". Nor does cartridge dimensions alone determine "headspace". Chamber length minus (-) cartridge length = headspace. Chamber gages (GO, NO GO and Field) have unfortunately and inaccurately been labeled "headspace gages". They are not. Their intended use to to verify chamber dimensions fall within acceptable limits. For newly built firearms, this means the GO gage should chamber and bolt should not close on the NO GO gage. For used firearms, the bolt should not close on the Field gage. Again, passing either of these tests does not define "headspace" because it ignores cartridge case dimensions. While we like to believe factory ammo comforms to rigid dimensions, that belief isn't necessarily true. You need to measure your cartridge case dimensions to determine if they are within acceptable dimensional limits. That's why case gages are sold. For a newby reloader, case gages are a necessity because their proper use assures you haven't bumped the case shoulder back too far and created unsafe headspace. With more experience, the advanced reloader can learn to adjust headspace for his rifle by controlling how far his case shoulders are bumped (or not bumped) during the sizing operation. Typically, a 0.002" difference between chamber and case dimension (the definition of headspace) contributes to best accuracy. |
I don't think 28 grains of 335 behind a 115 grain SMK is under powered load, but I could be wrong |
You are correct. That load should develop plenty of pressure to seal the case neck against the chamber. Some ball powders burn dirty. |
It's troubling that someone like you that thinks he knows what headspace is should say such a things about it. Headspace is a chamber measurement from the manufacturer or owner of the the chamber or chambering. Someone invents a cartride idea and cuts a chamber for it. Then the cartridge manufacturer makes cartridges to a minimum and maximum dimension to fit that chamber. The cartridge doesn't have a damn thing to do with the chamber dimension, it only have to fit it to the min/max standards. In the automotive world what is piston clearance? Is it the mismatch between the cylinder dimension and the piston dimension? Not hardly...there are set standards for both. |
Hmmm...I just checked the SAAMI website and found out what I had been taught was "headspace" is actually defined as "head clearance". I'll have to take it up with good ol' Jim, my gunsmith buddy who got me into shooting and taught me about "headspace". Live and learn. |
There was a big discussion about headspace on another forum. Let's say I'm correct and headspace is the chamber dimension from a certain spot to the bolt face. In the bottleneck case that is a datum on the shoulder to the bolt face. Well the big argument on the other forum was excessive headspace as the description for the amount of clearance ( I see you used that word) between the case head and the bolt face. I see headspace more often defined as I described it. |
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There are two ways to look at headspace. First, let's consider the practical definition, and follow up with the technical one. In practical terms, headspace is the clearance allowed between the base of the cartridge case and the face of the bolt. The position of the cartridge in the chamber is controlled in a variety of ways depending on the type of cartridge case involved. Most rimless automatic pistol cartridges (e.g., 9x19mm Parabellum, .45 ACP) are positioned by the case mouth resting on the front edge of the chamber. Rimmed cartridges (e.g., .45 Colt, .30/30 Winchester) are positioned in the chamber by the face of the rim resting on the rim recess at the back of the chamber. Belted magnum cases (e.g., .300 Win Mag., .458 Win Mag.) are positioned by the belt resting on the recess provided for it at the rear of the chamber, much as rimmed cartridges are. Finally, bottle necked rimless cartridges are positioned by the shoulder of the case resting against the shoulder of the chamber. So when a cartridge is chambered, it is positioned in one of the above ways. Once positioned, there must be a little free space between the cartridge case base and the face of the bolt, to allow for dimensional tolerances in cases. When the cartridge is fired, the case expands in all directions, including toward the bolt face. If there is the intended clearance space, the case head is not stretched excessively during this expansion. If the space is too much, as the case head is pushed backwards towards the bolt face it may stretch enough for it to significantly weaken the case in the area just in front of the thick portion of the case head, called the web, where the thinner walls of the powder containing part of the case begin. If the case head does not separate on the first firing, the weakened brass may do so on subsequent firing. This is a very bad thing, as hot gas at 50,000 psi will damage at least the stock and magazine, if not the firer's hands or face. Little drops of molten brass and brass shards are carried by the hot gas at near-supersonic speeds. If all the firer gets is a Chicken Pox-like tattoo, he or she is fortunate. Conversely, too little clearance is a bad thing, too. That is, if there is "negative" clearance and the case has to be forced into the chamber by the bolt, it can wedge the case neck tightly around the bullet, raising pressures by thus delaying bullet release. Then the hot gas will come out the primer pocket... The technical definition of "headspace" for bottle-necked rimless cases is the dimension between the bolt face and the datum line on the chamber or cartridge shoulder, whichever is being referenced. This is the source of the dimensions found in the Bruce Woodford chamber drawing below:  The "datum line" is a position on the shoulder defined by the military or SAAMI drawing as appropriate. One measures this dimension by means of a chamber headspace gauge. These can be graduated in explicit headspace dimensions (as are Match Gauges for the .308 Winchester) or in qualitative terms: Go, No-Go, and Field. (Chamber headspace gauges are available, of course, from Fulton Armory; see the Parts and Accessories Page for your rifle of interest!) The amount of clearance allowed for a nominally dimensioned cartridge can be inferred by this measurement of headspace. Of course, the actual headspace obtained (i.e., the clearance between the base of a chambered cartridge and the bolt face) depends on the "headspace" dimension of the cartridge, which can be measured by a *cartridge* headspace gauge. Hope this helps! --Walt Kuleck Fulton Armory Tim |
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Thank you Tim. My opinion still stands even though it might be technically wrong somehow. When I used the term "shoulder", I was actually talking about the datum line on the shoulder. My idea of checking headspace is that datum line distance to the end of the case. I like .004 to .006 headspace on semi-autos and .002 on SAAMI chamber bolt guns and .001 on my 6PPC and .223 with tight neck chambers. Dale McClure |
You mean .004 to .006 and .002 and .001 "clearance"....not headspace 
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I know what 5757 meant. Your measuring the gap between the bolt face and head case with the cartridge fully seated in the chamber. Correct? I think these bench rest guys like to eliminate any possible variable. I think you are spitting hairs with this discussion. Read between the lines terminology seams to vary some but you all can figure it out. wow AL |
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Velocity is on the right trail. Hey Mad, here's how, for example Remington, makes a 308. Hey chamber man, need a 308 chamber. He replies okay. Get a rifled 308 barrel blank, threads the end, and gets the chamber reamber for a 308. So he reams it, then gets a gauge , BUT takes some special measuring shims...and he says to himself I have to be able to get this .004 shim in there behind that chamber gauge. Nope, not good, have to ream alittle more. So he reams the chamber some. Back to the gauge and shoves his .004 shim in there and this time the bolt closes just snug. Yup, that's it, good enough. So Mad, I reckon you would call that .004 the headspace gauge huh? Well it's not and that story isn't how any manufacturer does it, not even a gunsmith. There is a measurement from a datum line on the shoulder of the chamber to the face of the bolt. That is a data specification chiseled in granite for what correct dimension for a 308 Winchester chamber is suppose to be. It's called headspace. That addition space you're talking about is "clearance", "slop", whatever you want to call it EXCEPT it isn't headspace. I haven't called you stupid like you have me, but I'll tell you this. Someone told me that your were a benchrest shooter or something to that effect. Well it's like this. You can be a race car driver, but not know a darn thing about automotive mechanics. Guess this must hold true to you, you may be a shooter, I don't know as I don't know you, but you don't know shit about the mechanics of firearms. Maybe you're a hillbilly firearms mechanic...This harrrrr is set for .004 headspace y'all. hahahahahahaha too funny. |
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Headspace is a term specific to the barrel chamber reloader and most shooter incorrectly use it to describe the case and how much room it leaves or how much they set back the cases shoulder which they measure from the datum line of the case not the chamber to its head. This is an improper but very prevalent use of the term with shooters as the two are related but are certainly not the same thing. Headspace is the measurement from the datum line of the chamber tot he bolt face. Reloaders an gun owners incorrectly but understandably use the term to mean the distance left between the datum line of the chamber and the datum line of the case when to bolt is closed with a case3 in the chamber. This space is and should be properly called setback as that is what it is. No matter how understandable the misuse of the term is it is still technically misuse and when used in a technical discussion can lead to confusion. This is compounded further by gun writers who once again add confusion and incorrect info when clarity is what is need and expected from them. That is how I see it. So many terms are used incorrectly. Like lead leade throat etc.. |
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Go to the SAAMI website for definitions: HEADSPACE The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. HEAD CLEARANCE The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace. HEADSPACE GAGE A device used in a firearm to determine the distance between the breech face and the chamber surface on which the cartridge seats. Also called Breeching Plug. LEADE (LEAD) That section of the bore of a rifled gun barrel located immediately ahead of the chamber in which the rifling is conically removed to provide clearance for the seated bullet. Also called Throat or Ball Seat. |
Just shows how throwing around these term can make things confusing. Glad you posted this. |
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