Case head and bolt face ?
- Thread starter 06shooter
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There's three situations.
One is with Mauser style claw extractors; M98 and Win 70 classic (pre '64) and M1903's, another is the sliding ones used in post 64 Winchesters, then the circlip or snap over ones used in Rem. 700 and Garands.
All of these will slip over a case rim then into the case extractor groove when the bolt's closed on a round hand pushed into the chamber.
When rounds are fed from the magazine:
Claw extractors on Mausers and control fed pre 64/classic Win 70's are set off the bolt face and the round's rim slides up into them as it leaves the magazine.
Sliding extractors slide out over the case rim as the round is chambered and stops against the headspace point and snaps over the chambered round's rim. Circlip/snap-over ones do the same thing.
Once the round's chambered, there's a few thousandths head clearance; the space between the bolt face and case head. It's maximum with the ejector's in the bolt face and pushes the round as far forward in the chamber as possible; it stops against the headspace point; belt or shoulder or rim, that is some distance from the bolt face to the chamber that's the headspace reference. Cases normally do not have their rim pushed against the extractor claw; there's clearance enough to allow easy chambering and the extractor to slide over the case rim.
In line ejectors push the case head off the bolt face so there's a few thousandths head clearance. Head space is the distance from the bolt face to the chamber reference; shoulder for rimless cases, belt ridge for belted ones or rim recess for rimmed cases
One is with Mauser style claw extractors; M98 and Win 70 classic (pre '64) and M1903's, another is the sliding ones used in post 64 Winchesters, then the circlip or snap over ones used in Rem. 700 and Garands.
All of these will slip over a case rim then into the case extractor groove when the bolt's closed on a round hand pushed into the chamber.
When rounds are fed from the magazine:
Claw extractors on Mausers and control fed pre 64/classic Win 70's are set off the bolt face and the round's rim slides up into them as it leaves the magazine.
Sliding extractors slide out over the case rim as the round is chambered and stops against the headspace point and snaps over the chambered round's rim. Circlip/snap-over ones do the same thing.
Once the round's chambered, there's a few thousandths head clearance; the space between the bolt face and case head. It's maximum with the ejector's in the bolt face and pushes the round as far forward in the chamber as possible; it stops against the headspace point; belt or shoulder or rim, that is some distance from the bolt face to the chamber that's the headspace reference. Cases normally do not have their rim pushed against the extractor claw; there's clearance enough to allow easy chambering and the extractor to slide over the case rim.
In line ejectors push the case head off the bolt face so there's a few thousandths head clearance. Head space is the distance from the bolt face to the chamber reference; shoulder for rimless cases, belt ridge for belted ones or rim recess for rimmed cases
jason.jardine72
New member
.007 to .014 on a Remington 700 if you only had .001 you would need a clean room to shoot In because a spec of dirt would either prevent bolt closing or a possibility of slam fire when you close the breach and something on the bolt face depresses the primer ! Also if under immediate expansion of the gases at the point when the bullet molecules change frome a solid state to a term called plastic state just then the case expansion occurs sealing the chamber gasses away from your face and safety glasses it if you measure can expand up to .005 in all directions depending on the quality of the chamber die used or chamber wear. Neck sizing your casing with rcbs or Lee if you can send them 5 spent casings and your full length die they will perform a hone on the inside of the Lee die the same dimensions of the chamber so when you full length your Lee die it only forms the neck (seems like a lot of work just buy a neck die from rcbs and only full length every 5 firings annealing every 5 as well .. Some people experiment with the amount or length of neck sizing maybe just doing 1/4 1/2 of the neck enough to hold the bullet that's it !!! This is the ultimate in casings long life 40 plus reloads !!! There will be a ring of brass building up at the base of the neck I've heard of people turning there casings but it is wrong you must re incorporate the ring back into the casing to maintain safe wall thickness winchester having the thinnest I've measured at .0125 and a surplus military having .0180 the thickest I've measured Remington is .015 lapua is .014 Norma .014 all measurements were on the 308 casing and I don't know about the webbing !!!! I researched this for the M118 LR the M118 uses lake city brass but the volume of the lake city brass is bordering on going non - supersonic at 1000 yards so is most others when the M24 needed a new temporary bullet till the more powerful M40 could replace it the M118LR was developed using winchester brass which I thought was no good because of the thinnest walls but the volume I think is 58.5 cc of water and this kept in line with specific guidelines of a 1000 yard 7.62X51 bullet but even with today's powders only a few will keep a 308 super sonic at 1000 yards it's been a large development in projectiles and there BC's that have Givin us the opportunity to see more people setting there goals at 1000 !!!!! I read yesterday that in projectiles nothing bad ever came out of a green or a yellow box !!!! And soon to be tested by me very new and quite popular 208 grain A MAX and 208 grain Match both with the AMP Jacket !!! This is the heaviest bullet I could find a load for in 308 !!!! Top of my head BC 600 maybe just shy of it !! These will turn the short action king into an empowered rifle likes of which we need!!! Proper shot placement out to unheard of distances with and supercharged heavyweight 308 testing needs to be done I can only guess but The 308 isn't being pushed out the door by any gun !!! So to answer your question on a Remington 700 as you rotate the bolt to lock it it slightly jumps ahead that is the case head going into the recess if you were to take a dial indicator and put it on the end of your bolt had push forward hard on your bolt it springs back and forth you can measure available head space as long as wear doesn't cause your handle to contact the receiver or stock but you would have noticed that wear long ago F class try for 5 to 6 thousands end play .0025 at each end or some equalization in there of the two numbers !! Hunters with dust in the air leaves grass etc getting accidentally into your recovers time for .010 to .014 so the bolt will slide and close smoothly even with a dirty rifle about as thick as a piece of paper !!! These measured tolerances are purposeful to the hunter for a reliable rifle and us long distance shooters spend 1000's $ extra tightening it all up squaring this lapping that fitting he and removing there in our quest for 2500 yards out of a 6 mm bullet because 1000 just isn't far enough anymore with these March 8X- 80X power scopes there selling for 7 grand
jason.jardine72
New member
jason.jardine72
New member
Haha !!!! At least it wasn't the most !!!! You just have to step back and see it all at once instead of little pieces at a time !!! That is why they say communication is a two 2 at thing it includes eye contact body language understanding the little things before moving forward with a conversation with someone sort of response !!! You can't get that in writing a one sided story plus I'm guilty of not using punctuation !!!!! Believe me in a two way communication you would understand !!!
JJ72 says:
And primers typically need to be dimpled at least .020" so if a tiny hard thing's tinier than that in diameter, it won't cause a problem if it's between the bolt face and primer when the bolt closes even in a zero head clearance system.
Neck only sizing fired .30-06 cases ends up with them having only about .001" head clearance. You've got to full length size them to have any more. If they rifle's got minimum chamber head space, to start with, I doubt you'll ever have more than a few thousandths head clearance; never as much as you would like.
LC 7.62 NATO cases, match or service, have had plenty of room for powder charges to shoot all 30 caliber match bullets fast enough to stay supersonic through 1000 yards since 1964; with safe pressures, too. The issue of subsonic bullets came from people shooting M852 match ammo with Sierra 168's in barrels oversize in groove diameters or the right size but worn out with too much throat wear. Most often with M14's and M1A’s with 22 inch barrels. Garands with 24" barrels rarely had a problem; none of the four barrels in them I wore out had subsonic bullets at 1000 yards.
Best head clearance on bolt guns is about .002". That’s the slop between the bolt face and case head when the round’s full forward in the chamber. For others including semiautos, about .003" head clearance is best. That’s been the norm for decades. Maximum head clearance allowed by SAAMI can be seen by checking their specs for cartridge case and chamber dimensions. Such head clearances have never been a problem with 99.9% of all rifles.
And primers typically need to be dimpled at least .020" so if a tiny hard thing's tinier than that in diameter, it won't cause a problem if it's between the bolt face and primer when the bolt closes even in a zero head clearance system.
True, but typically not a problem.
Considering the fact that proper full length sizing fired cases has resulted in dozens of reloads per case when normal, safe maximum SAAMI spec pressures are used. Besides, full length sizing fired cases has proved to yield best accuracy for decades. The benchresters finally switched over to that some years ago. Sierra uses Redding full bushing dies for all cartridges they’re made for with their bullets for accuracy testing; standard full length ones for the rest. I’ve got better accuracy with new cases than neck only sized ones with the best neck dies made.
Neck only sizing fired .30-06 cases ends up with them having only about .001" head clearance. You've got to full length size them to have any more. If they rifle's got minimum chamber head space, to start with, I doubt you'll ever have more than a few thousandths head clearance; never as much as you would like.
I’m aware of that dreaded neck donut, but I’ve never had one big enough to get concerned about.
LC 7.62 NATO cases, match or service, have had plenty of room for powder charges to shoot all 30 caliber match bullets fast enough to stay supersonic through 1000 yards since 1964; with safe pressures, too. The issue of subsonic bullets came from people shooting M852 match ammo with Sierra 168's in barrels oversize in groove diameters or the right size but worn out with too much throat wear. Most often with M14's and M1A’s with 22 inch barrels. Garands with 24" barrels rarely had a problem; none of the four barrels in them I wore out had subsonic bullets at 1000 yards.
Sierra’s 240 and 250 grain match bullets have been shot from .308 Win. cases through a 1:8 twist barrel with excellent accuracy at 1000 yards winning matches at that range. Muzzle velocity with around 43 grains IMR4350 is only 2150 fps or so, but they buck the wind very well indeed. You’ll need a longer leade (chamber mouth to where the angled throat starts.
If there’s any head clearance in your rifle with the bolt closed, it goes straight to maximum when the firing pin smacks the primer and before the primer fires. With in inline ejectors in a bolt face, they push the round full forward before the firing pin hits it anyway; again max clearance between bolt face and case head; zero between case headspace point and that of the chamber.
No competitive shooter wants that much slop in head clearance. Neither does the military folks. Case life is shortened as head clearance increases. A fired case is driven hard into the chamber then expands at the front part first, then the back part. There’s enough force to set the case shoulder on rimless cases back a few thousandths. Primers usually back out past the case head a little then get pushed back in as the back half of the case stretches the case head against the bolt face. The brass 2/10ths inch in front of the case head gets stretched the most as well as shrunk down by sizing dies; all resulting in metal fatigue over time. Keeping head clearance to a minimum alleviates this stuff and increases case life as well as accuracy; the more the case stretches back, the more out of square the case head gets and that causes accuracy problems. Minimally sizing cases helps.
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jason.jardine72
New member
You did a fair job understanding Bart !!! Like I said communication is a two way street! !!+
jason.jardine72
New member
Waste!
You missed the point, you have two standards, either the case fits the chamber with minimum clearance or as Mr. Hull said, it is the bullet, the case can fit the chamber like a rat tur& in a punch bowl.
I am the fan of cutting down on all that case travel, I am the fan of forming cases to fit.
F. Guffey
Martin Hull's point was, and still is, the case needs some clearance around its body for bullets to shoot accurately; they must not interfere with the chamber body and neck walls whatsoever. There can be minimal clearance between the bolt face and case head, case shoulder to chamber shoulder will naturally have zero clearance, as well as a little or no clearance at bullet and throat at the origin off the rifling. I talked with him in the 1960's about that. He was a good friend.
Some people don't understand that. Benchresters finally did some years ago when they started full length sizing their fired cases and gave up neck only sizing.
Some people don't understand that. Benchresters finally did some years ago when they started full length sizing their fired cases and gave up neck only sizing.
Full circle, we are back to bench resting "Here is how the bench resters do it" They do not go to the range with the same rifles, it is unusual for one to go the same range. I was at a range when asked if I was a bench rester, I ignored the inquisitive shooter. He went to the desk and ask Dottie, She did not know so she called my wife, Dottie informed the inquisitive shooter he should mind his own business, Dottie did not think the inquisitive shooter would understand and or appreciate my wife's answer.
F. Guffey
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Just trying to nail you down on this matter, there are some that can tell funny stories, there are some that should not. Then there are those that try to make themselves look good at other expense. Any reloader with a Sierra reloading book can read about Mr. Hull.
F. Guffey
Guffey, I don't think you get the bigger, realistic picture; none of what's in Sierra's manuals and web site, too, for that matter. Anyone gleaning Sierra's reloading manuals will see less than 1% of the reloading information he shared with rifle competitors shooting matches with him so they, too, could make the most accurate ammo possible. Especially when he gave them a tour of Sierra's plant showing and explaining stuff to them.