Head space

[Newfie]

Actually what I am interested in knowing is not about head space but rather bolt to breech clearance.
I understand that different cartridges head space differently. i.e. on the shoulder, rim etc. and how it is measured from the datum. At least I think I do. LOL
What I am interested in knowing is the difference in clearance measured by head space gauges. For instance, lets say that the clearance between a :go" gauge and the bolt face is 0.
( I am just picking numbers for ease of explaining) What is the distance between the bolt face and a "no go gauge"? How about a field gauge? Another way to say it mightbe what is the tolerance allowed between go gauge and a no go gauge? Am I making sense? From researching and reading I am thinking it is around .004 of an inch from go to no go. No idea what it is for a field gauge.
If I know the allowance seems I could use a known thickness shim material on a go gauge and have a no go gauge. Same for a field gauge.
Also, if cartridges are loading, firing and ejecting ( everything cycling properly) is a go gauge needed? Seems to to me for an already assembled rifle a single no go gauge is what would needed. Where as a go gauge would be needed for initial assembly during a build or re barreling of a rifle.
Comments?

[WARFAB]

Interesting question and I'd be curious to hear a thorough explanation from one of the experts here on the forum.

My impression was that go/nogo gauges were used in initial fitting and assembly before a round is ever fired out of the rifle. If you've already fired a round and everything works fine, it seems like you don't really need to use the gauges. It's just risky to determine if headspacing is correct by shooting the rifle.

[camper4lyfe]

What WARFAB said. By the time you've fired it, you're past the point of needing a gauge (for the most part).

[Newfie]

What WARFAB said. By the time you've fired it, you're past the point of needing a gauge (for the most part).

I hear what you guys are saying and I would agree. I have seen no indication of case stretching or case head separation. However the ammo is steel case and I wonder how prone they are to stretching. I do remain curious due to the combination of parts in the rifle. It is an SKS and the bolt obviously is not matched to the receiver as the bolt has absolutely no markings or numbers of any kind. The receiver, bolt carrier and the trigger group are matching numbers. So at some point someone must have replaced the bolt. I believ that headspacing when replacing a blt is adjusted by removing stock from the lower rear beveled area on the bolt where it drops down next to the locking bar. Someone may have just thrown the replacement bolt in and never checked head space or they may have taken th time to fit it properly. Or they may have tried to fit it and did it improperly. So though the rifle is functioning I rekain curious.
I am also wondering if wxcessive head space has an effect on accurracy.
Just curious.

[Meketrefe]

You can headspace a rifle w/o a gauge and be perfectly safe. What you need is a formed case exactly as they come from your loading process. Most times the case dimensions are taken
form the resulting case after full length re-sizing or a few rounds from the factory loads you want to use. During the final headspace / chambering tuning you want these cases to be snug
but not forced. This means there is zero tolerances. This is how match rifles are headspaced. Zero tolerances so the chamber is a perfect fit to the desired case. Gunsmiths will still check
with the gauges but it is really not necessary at this point. If you want to give an extra clearance a small piece of scotch tape will give an extra 1-2 thousands.
Also keep in mind that after torquing down the barrel the headspace might grow or reduce by another 1-2 thousands. In case of a regular shank it will shrink but rilfes using the barrel nut
system like savage it might increase, depending on the state of the threads and other factors. But with he barrel nut you have more control so it is easy to adjust w/o extra cutting or reaming.
After that all you have to make sure you are using ammo of the same dimensions +/-tolerance that you gave to the given cases. In case of match shooters this tolerance is zero or very close to zero. And they can afford this because they have the equipment to produce the brass identically or they demand from specialized vendors who reload for them to be done with those tolerances. For the average shooter folks might give an extra 1 thosand or 2 depending on how
forgiving you want your chamber to be and what kind of consistency you get with your ammo. For surplus from all over one might give even a larger tolerance.
Field gauges tolerances change depending on the chambering and some are off anyway so one should not trust them w/o measuring them.
The tape method is as good as any other system and better that most field gauges anyway. Your calipers and micrometers are your best friends.

I hope this answers your question.

[thughes]

Saw a debate like this recently in another forum. One of the members on that forum is also a well known manufacturer of head space gauges. His input: If the bolt closes on a round, there is no need for a "go" gauge (the "go" gauge is really most relevant to the initial sizing/reaming of the chamber).

[Meketrefe]

Saw a debate like this recently in another forum. One of the members on that forum is also a well known manufacturer of head space gauges. His input: If the bolt closes on a round, there is no need for a "go" gauge (the "go" gauge is really most relevant to the initial sizing/reaming of the chamber).

Correct. I think it makes sense as a reference where one should stop and check even before getting there during chambering / headspacing. There is a catch though, the go gauge must be useful if "Bubba" (the ktchen gunsmith) is trying to chamber a rifle verifying with a dummy brass or manufacturer round and in the process he is crashing the brass so that check is all screwed up. He will not be able to crash the hard steel go gauge so from that perspective Bubba and his buddies might be safe if they use the gauges. But otherwise for a real gunsmith there is no need for neither the go nor no go if they have the rounds intended to be fired but professionals do the gauges anyway. ...you know, gives a peace or mind, murphy's law and all that.
I have chambered my rifles and done it with the brass only but I am very careful and know what I am doing and I am looking for extreme accuracy anyway.

So since this is a thread for folks to learn tell me two ways you can have a chamber all screwed up and still pass the headspace check? I have seen AR15 barrels delivered like this.
So when someone tells me there is no need to check headspace in an AR15 barrel or any other barrel or rifle purchased I know they are full of bull byproduct but what other things
we need to check even if the headspace is ok? These are rare instances but, you know, schit happens.

So come on guys, tell us! ..... knowing your firearms and ammo is as important as good marksmanship qualities.

[Newfie]

Correct. I think it makes sense as a reference where one should stop and check even before getting there during chambering / headspacing. There is a catch though, the go gauge must be useful if "Bubba" (the ktchen gunsmith) is trying to chamber a rifle verifying with a dummy brass or manufacturer round and in the process he is crashing the brass so that check is all screwed up. He will not be able to crash the hard steel go gauge so from that perspective Bubba and his buddies might be safe if they use the gauges. But otherwise for a real gunsmith there is no need for neither the go nor no go if they have the rounds intended to be fired but professionals do the gauges anyway. ...you know, gives a peace or mind, murphy's law and all that.
I have chambered my rifles and done it with the brass only but I am very careful and know what I am doing and I am looking for extreme accuracy anyway.

So since this is a thread for folks to learn tell me two ways you can have a chamber all screwed up and still pass the headspace check? I have seen AR15 barrels delivered like this.
So when someone tells me there is no need to check headspace in an AR15 barrel or any other barrel or rifle purchased I know they are full of bull byproduct but what other things
we need to check even if the headspace is ok? These are rare instances but, you know, schit happens.

So come on guys, tell us! ..... knowing your firearms and ammo is as important as good marksmanship qualities.

If the chamber is not properly sized so that when the cartridge seats it might place the case head and primer a distance from the bolt face that is incorrect.
When you grade me Meke, please do tell the difference in tolerance between a go and no go gauge. Was I close when I said .004 inch?
If so, I can make a crude no go gauge by placing .004 of the tape on a new unspent cartridge. Say maybe 2-3 layers of scotch tape. Would this be correct? Do the test with the extractor and FP removed using finger pressure on the bolt.
Correct?

[Meketrefe]

If the chamber is not properly sized so that when the cartridge seats it might place the case head and primer a distance from the bolt face that is incorrect.
When you grade me Meke, please do tell the difference in tolerance between a go and no go gauge. Was I close when I said .004 inch?
If so, I can make a crude no go gauge by placing .004 of the tape on a new unspent cartridge. Say maybe 2-3 layers of scotch tape. Would this be correct? Do the test with the extractor and FP removed using finger pressure on the bolt.
Correct?

Gauges change sligthly with brands and chambering. Not by much but they can be different, due to both spec or +/- tolerance error.
Here I need to know the precise chambering you have. Are you talking about 223R?
Initially the scotch tape is a great method. Differences can go up to 6 thousands as you can see below. So measure the thickness of the tape with the calipers and apply accordingly.
I would say it might close with two layers but never with 3. 1 layer should be fine. 2 already showing some resistance. 3 leyers no go. ... but because this is subjective to the tape you are
using better measure the tape. Never make any assumptions.. the hazy / hard tape is the best. when I say resistance I mean like with the tip of your fingers almost letting the bolt drop not
ramming or forcing anything. Needless to say the ejector and pin need to be removed to get a reading w/o any interference.
If you are doing the tape method the field measure is pointless but this do with care. Better verify with the brass you intend to shoot too.


This is from PTG gauges...



I got this form form AR15barrels.

Gauges organized by dimensions: Gauge Spec Size Range
Civilian GO 1.4640" 1.4640"
Military GO 1.4646+0.0002" 1.4646" - 1.4648"
Civilian NOGO 1.4670" 1.4670"
Civilian FIELD 1.4700" 1.4700"
Military NOGO 1.4706" -0.0002" 1.4704" - 1.4706"
Military FIELD 1.4730" -0.0002" 1.4728" - 1.4730"
Colt's FIELD II 1.4736" 1.4736"

[Meketrefe]

If the chamber is not properly sized so that when the cartridge seats it might place the case head and primer a distance from the bolt face that is incorrect.
When you grade me Meke, please do tell the difference in tolerance between a go and no go gauge. Was I close when I said .004 inch?
If so, I can make a crude no go gauge by placing .004 of the tape on a new unspent cartridge. Say maybe 2-3 layers of scotch tape. Would this be correct? Do the test with the extractor and FP removed using finger pressure on the bolt.
Correct?

That would be the headspace. So assuming the headspace is ok what other measures are critical and sometimes barrel makers and/or cheapo parts gunsmiths screw up?

[Newfie]

That would be the headspace. So assuming the headspace is ok what other measures are critical and sometimes barrel makers and/or cheapo parts gunsmiths screw up?

Trying to picture this in my mind. I am thinking that if the chamber is out of spec. In regards to diameter it would still be possible in some circumstances to have the headspace correct. Would this allow excess case expansion?
Or, could what I am chasing have anything to do with proper barrel indexing?
In some rifles can't the headspace be altered by calculating the thread pitch to determine how far the barrel travels for each complete turn and then altering the length of the threaded portion the appropriate amount?

[WARFAB]

[QUOTE=Meketrefe;n37857This is how match rifles are headspaced. Zero tolerances so the chamber is a perfect fit to the desired case.[/QUOTE]

Now you have me wondering about the reloads I shoot. The handloads I shot for years in my AR were so tight that I would be hard pressed to open the bolt after a round was chambered. It was TIGHT. If I wasn't sure if I had successfully chambered a round I would tug on the charging handle and if it wouldn't move I knew a round was chambered. I never had any malfunctions or issues. More recently I was talking with some guys about doing a chamber check where you use the charging handle to pull the bolt back to expose a round to confirm it's in the chamber. Most people seemed to think this was a common practice for AR users so I concluded that my rounds must be too tight. I have since started shooting brass that is resized slightly more so that it's not quite as tight. Did I lose accuracy by making this change? The brass isn't sloppy in the chamber, but it's not as tight as it used to be.

[camper4lyfe]

Now you have me wondering about the reloads I shoot. The handloads I shot for years in my AR were so tight that I would be hard pressed to open the bolt after a round was chambered. It was TIGHT. If I wasn't sure if I had successfully chambered a round I would tug on the charging handle and if it wouldn't move I knew a round was chambered. I never had any malfunctions or issues. More recently I was talking with some guys about doing a chamber check where you use the charging handle to pull the bolt back to expose a round to confirm it's in the chamber. Most people seemed to think this was a common practice for AR users so I concluded that my rounds must be too tight. I have since started shooting brass that is resized slightly more so that it's not quite as tight. Did I lose accuracy by making this change? The brass isn't sloppy in the chamber, but it's not as tight as it used to be.

What I've read is that you need to resize the cases for semi autos. You don't need to with bolts, though.

[Meketrefe]

Now you have me wondering about the reloads I shoot. The handloads I shot for years in my AR were so tight that I would be hard pressed to open the bolt after a round was chambered. It was TIGHT. If I wasn't sure if I had successfully chambered a round I would tug on the charging handle and if it wouldn't move I knew a round was chambered. I never had any malfunctions or issues. More recently I was talking with some guys about doing a chamber check where you use the charging handle to pull the bolt back to expose a round to confirm it's in the chamber. Most people seemed to think this was a common practice for AR users so I concluded that my rounds must be too tight. I have since started shooting brass that is resized slightly more so that it's not quite as tight. Did I lose accuracy by making this change? The brass isn't sloppy in the chamber, but it's not as tight as it used to be.

Initially the least you re-size the brass the better. Many folks full resize the brass when using for autoloaders because they want to prevent malfunctions and then they can use their loads
with different rifles perhaps among several autoloaders and barrel makers. Because the slight differences in chambers the smaller size of the fully resized brass guarantees that this will chamber smoothly in any of the rifles. But if one is shooting for extreme accuracy one should try to neck size first only. By neck sizing only we are not reworking and deforming the brass back and forth, we are only adjusting the neck to take a next bulllet. So if the rifle functions fine with the autoloader then there is no need to overwork the brass and potentially loose accuracy. In the extreme accuracy world like bench rest folks do not fully resize the brass but the first time they shoot that chamber to fireform. Even after a chamber has been built to match a specific round or precisely to match SAAMI dimensions, they do this. But in the AR resizing also doesn't mean that you might see considerable accuracy impact as these guns are not on the top in terms of extreme accuracy. So one needs to take this gradually and see what is the best compromise. So avoid the small base dies that are even tighter. I have yet to see a chamber that is properly chamber that needs small base dies folks are selling. If your round was getting stuck is also not a good thing. One might feel a bit more resistance than a loose fully resized round but nothing like being stuck. This could be a sign of other issues. If you want I am happy to take a look and perhaps give you some suggestions. I think if one can build a copycat presicely of top of the line match ammo like lapua or federal gold match that is a very good thing given the chamber is tight and properly done. Who chambered your rifle and that type of 223 chamber do you have? if you know the reamer
it was cut with that would be awesome.

[Meketrefe]

Trying to picture this in my mind. I am thinking that if the chamber is out of spec. In regards to diameter it would still be possible in some circumstances to have the headspace correct. Would this allow excess case expansion?
Or, could what I am chasing have anything to do with proper barrel indexing?
In some rifles can't the headspace be altered by calculating the thread pitch to determine how far the barrel travels for each complete turn and then altering the length of the threaded portion the appropriate amount?

Ok you got one!! The problem that is someone screwing up chambering with a run-out creating a chamber slightly off center where the body dimension is wider than the allowed tolerances. This can happen at the beginning and if corrected will be automatically fixed later as we ream further but if one continues this might become very critical specially at the base. A case is more flexible toward the top so here it can adapt but towards the base will create a lot of stress in an areas that is critical towards the web. This is not supposed to be expanded and contracted, only as the necessary by the tensile strength of the brass but not to be reworked every time we resize the brass. Or if the chamber is too bad it might compromise the case and rupture with high pressure hunting or military rounds. Also accuracy will suck but if the runout was fixed in the last .200-300" (just a guess) perhaps will not be too noticeable but the chamber will be screwed up and the chamber might pass headspace. This is rare as most folks chamber with floating reamers but if the operator doesn't pay attention it can happen if the reamer holder gets some chips in the floating area and it doesn't float anymore or something with the machine chuck or something. Professionals check for everything but also schit happens. A good way to check this is to take some simple measures of the chamber with the calipers to see if the chamber at the base and inside is fine (also visual inspection). One might resize a piece of brass and check for any sloppiness. One might also cut the rim from the brass or file it down (after resizing of course) and start the case reversed. the case should stop at the base that is the critical dimension and do not go in more than few thosands because of the small flare in the chamber to help with chambering and a +.5 thousand tops tolerance, Use the caliper as some dies might be off (make the brass too tight) and in this case is not the problem of the chamber but the die like some small base.
The case might not show sloppiness due to be ok at the shoulder area and a tad beyond but not at the base. So one could cut the resized case in the middle and put only the bottom half at the right deth and see if that shows some sloppiness. No space should be ever be noticeable between the base and the chamber other than the flare at the entry of the chamber to help the bullet go in.
I am explaining this because I have seen this screwed up in "el cheapo AR" parts kits and barrels. and if we compound this with "el cheapo weekend deal AR carbine" over gassed systems and early extractions it only makes things worse and a recipe for disaster.

so what is the other chambering screw up that someone can do even with the headspace being ok?