Headspace confusion
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  1. #1
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    OK, I admit I may be over thinking here.

    Is it as simple as taking the distance from the back of the breech to the bolt face to get proper headspace gage protrusion?

  2. #2
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    Rimfire headspaces on the rim. I think most rimmed cases do also. Belted cases headspace on the belt. Thebarrelman

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    Just to add to Butch's, bottle neck rounds, or rimless, 308, 3006 ect. its some place between the neck and shoulder caled the date something line, I know what its caled just can't spell it. Auto rounds 45ACP and 9 MM use the case mouth.

  4. #4
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    think its called datum line ( memory?) usually SOMEWHERE near middle of shoulder ....object is to end up w/ abt .002 clearance between bolt face& rear of max.cartridge for tight hdspce .....on military sprgflds , they went back to armory somewhere between .006 & .010 .....however every military mauser i checked(many) was over .010, & several russian 7.62 x 54 also....soooooo go figure .....mcfarland wrote commercial mausers exported to USA were also .010, but that the germans didnt mind killing a few civilians between wars!!.........these datum lines are on cartridge book drawings & on some of my old reloading manuals ......incidentally ,u can make ur own hdspce ga. quite quickly ...turn up a piece of steel to fit rear of chamber w/ a shoulder the thickness required ( max case rim + .002 )....for rimless turn up a piece of double diameter, chamber d. at rear & DIAMETER of datum line for short section in shoulder area.make it the stated length fron datum line to rear end of max cartridge + .002 ...these are go gages .....004 more for no go ..BE careful using rimless ga. ,that u dont chamfer/ROLL the edge over as it is not hardened....have never barreled up a belted ( reckon no one thot there was anything big enuf in ky./ohio/ ind. to warrant one 40 yrs ago ) , but think rimless ones hdspc on datum line also .......if u are picky abt rimless ga., set up the sine bar on ur compound & turn up the commercial type ga. w/ full shoulder ....if really picky , do same w/ O-1 abt .010 oversize , torch harden , draw in kitchen oven @ 375 for 1 hour & toolpost grind to spec....have done it all ways & first one works just as well for me ......w/ bolt design having unsupported case heads ,if u have an incipient head fracture that lets loose , tight hdspce "machts nichts" ..better have a gas escape hole somewhere in receiver( & a pair of glasses ) i have been on the firing line when an action let loose three points away, & dont ever want to see( or hear) another .....
    FWIW last summer ,put a 308 sporter barel on a mauser ..no ga. & NO TIME ..transportation to texas LEAVING ....grabbed 1/2 dozen pices of new brass ,dab of grease on cartridge end , some .002 shim stock & chambered so it would take any of the six .....it was checked in texas & was .001 over minimum hdspc...( nephew never has sent me a check for the cost of the barrel ! ) point being , u dont always have to have all the "NECESSITIES " to do a workmanlike job (& maybe ,get paid for material before delivering freebie labor)

    best wishes
    docn8as

    PS THIS DOES NOT MEAN GET SLOPPY , but hdspce bugaboo has been badly overkilled by "sports pundits"(also damascus shot barrels ....that ought to stir up some dust!)....if EVERyTHING else is ok ,modern actions will stand a lot of hdspce abuse

  5. #5
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    forgot to mention that if possible, several brands of brass shud be used when gauging w/ brass & shims ( gillete blue blade used to be .0035 or so & lots of pieces were used )result of using only one brand may be too tight a chamber for some brass ....have also fulllength sized brass ,smoking shoulder to make sure i didnt set it back ,when i didnt have new brass ....now obviously , if shipping a rifle for a beastie that would just as soon track the hunter , u dont fool around ( & check ur ammo thru the action before setting out)....

    best wishes
    docn8as

  6. #6
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    I believe you need a go guage for chambering always. No need for a no-go if you do it right. I chamber through the headstock, cut the threads first, fit the action/bolt clearance to barrel (coned, flat, or recessed) by screwing the action on the barrel and measuring. Once the action fit is proper, start chambering, check your progress by screwing the action on the barrel with the go guage in place. When it bottoms out, measure the gap between the front of the action to the barrel shoulder with a feeler gauge. Advance the reamer to take up that clearance, but check often. When you get to zero, you should feel just the slightest resistance when closing the bolt on the go gauge. Take the reamer in another .002" to account for the torquing of the barrel. If the barrel shoulder and action face are true, you will be dead nuts. Check headspace again once torqued.

  7. #7
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    a sound discipline ......i barreled between centers ,first out of necessity ,later out of choice.....but used a mounted t/stock spindle indicator to complete reaming .( indicator on t/stock bearing on split clamp on spindle)..returning the t/stock body to battery after clearing chips always drove me crazy ...solution was another indicator against front of t/stock body ...so simple ..thnx walt mueller ......t/stock chuck on reamer ,against washer against tap wrench ,about .010 LOOSE makes a poor boy floating reamer holder for those financially compromised ......friend of mine that holds two national records ,chambers w/ tight chuck & LOOSE t/stock ..shoves it along ....each smith finds his own way ...& what 's important is the results he obtains
    ......but i feel the more methods a tyro is exposed to , the broader & quicker will be his developement today ,much more info is around than 50+ years ago ...there was much erronious & incomplete info perpetuated by gun writers , probably some inadvertantly by me as i was gun editor of hunting dog magazine,for a year or so ....getting the details of proper barreling up was like pulling teeth (i know something abt that also,)( trade secrets prevailed) i commend todays smiths for their willingness to share


    best wishes
    docn8as


  8. #8
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    Doc, I think that you will find the belted magnums headspace on the belt. I think most accuracy smiths headspace like a normal bottle neck rimless case when doing accuracy work though. Regards Thebarrelman


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