headspace ?

[clodbuster]

Is headspace set for each gun model or by the cartridge? A gunsmith told me you can use layers of tape on the cartridge head then chamber the case and try to close the action.  Remove the cartridge and measure the cartridge overall length gain from the tape.  Keep applying more layers of tape until you can't close the action and you have a no-go gauge.  What about it?  Where can I find the headspace should be?

[dcb]

head space is set by the cartrage for that action barrel combination.
 A rimed case has its headspace set by the rim.
 a belted magnum is set by the belt.
 A rimless case is set by the length, measured from the base to a datum line on the sholder.
 The gun smith is correct in by using tape to check head space. nogo guage..
 It does take a lot of consideration as to the feel and fit of the bolt on the dummy cartrage to measure the length.
 Its more involved than he has made sound.

[gunnut69]

Headspace is determined by the individual rifle.  It is a measurement from the bolt face to some point in the chamber, the datum line on the shoulder(rimless case) the front of the rim (rimmed case) and the front face of the belt recess(a belted case. I don't think the tape idea is a good one as it would be easy to apply a bit of pressure and alter the measurement..  Headspace guages made of steel can be damaged or the chamber you are checking can be damaged by forcing a bolt closed with the guage installed.  A bolt rifle developes a lot of camming force and can easily force the shoulder back on a case..  Even if care is used and nothing is deformed, what have we measured.  Where is the 'datum line' on the shoulder of the case..how can you take the measurement.?  It may be possible to use a 'go guage' and brass or steel shim stock to determine the amount of excess headspace existant in a rifle but even that can be deceiving.  There are adhustable headspace guages available that can give us the exact measurement but they are a bit rare and pricey to boot.  A go / no go guage set will keep us safe and will cost less than $35 new..

[tuck2]

Each rifle chamber can vary somewhat and still be within specs. Stoney Point sells a Headspace Gauge with which you can compare the length of unfired and fired cases. One than can adjust the reloading dies to better match the case to the rifle chamber. I find that belted and rimed cases will last longer when the dies are set on the base to shouler length.

[gunnut69]

tuck2 is absolutely right.  This process makes the belted and rimmed cases (they must have a shoulder) headspace on the shoulder rather than the belt or rim..  The simplest way to do this is to take a case fired in the rifle being loaded for.. (both tuck2 process and this procedure will only work for ammo for a specific rifle) and using a magic marker color the cases neck.  The case is lubed lightly and run into the FL sizer with it backed at least a 1/4 inch from the top of the shell holder.  Screw the die into the press running the case in and out and watching the mark on the neck until the mark is JUST removed to the shoulder....  don't allow the sizer to set the shoulder back.  When this is done lock the die down with it's locking ring.  This is called partial sizing and creates a more precise fit between the case and the rifle's chamber.  Ammo loaded this way may or may not fit in another rifle of the same caliber, it has been set for the rifle it was initially fired in.  If the cases over time get to where you can feel the case in the chamber when closing the action simply adjust the die to 'kiss' the shoulder.. just slightly move it back..  It will then be just fine again.  This is because the 'spring back' of the brass is lost after several firings.  Setting the shoulder back will restore free action to the cases again.  The Stoney Point tooling allows this to be formalized and measured, but at the cost of a fairly expensive set of tooling..  I've some 222 Rem brass that's been reloaded this way for many years..  I'd have to check to find the actual number of reloads,,it must be near 30 by now for some of it...  I started loosing some at the last loading and thought about annealing the necks(that's how cases reloaded this way usually give out, cracked necks) but decided 20 years is a good long life and will replace them..

[clodbuster]

Gunnut69  I know some people make a reloaded cartridge by seating a bullet out to touch the rifling and slightly reducing the load to avoid overpressure then firing this round to size it to the particular chamber.
The rifle concerned is a Marlin 62 in 256 winmag.  What do you think of the "seated out bullet" practice?

[gunnut69]

This is a trick used by folks making brass for a round where the shoulder needs to be moved forward.  The 256 is a rimmed round(necked down 357) and this does not need to be done to fireform a case to the chamber.  With rimless cases where the shoulder is farther farward than is the 30-06's shoulder this is one way to create a temporary headspace to allow the case to fire and be formed to the chamber.  Another method is to expand the neck to the next large size. For instance if we were creating a 30 caliber wildcat with the shoulder further forward I could expand the neck(using the normal processes) to perhaps a 35 caliber..  This case would then be run thru the sizing die and a small shoulder would be created that could be used as a temporary headspace to allow fireforming..  In this process I prefer to use cream of wheat held in the case with a wax plug..  A fairly still load of a fast burning powder will usually create a fully formed case with nearly no losses.  The cases will have the be annealed during the necking operation and perhaps after the forming operation.  this is only to give the headspace something to set against, the 256 has no need of this or the bullet seated into the rifling to generate resistance to cartridge movement from the firing pin strike..  the rim will headspace the case quite well.