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View Full Version : Help - i think my headspace is too loose!


twistedneck
February 14, 2009, 15:33
This is the second gage i'v put it. first was 247, now i'm at 0.255.. thinking about buying the next dsa size up.

WHen i do the thumb trick, it has ever so slight resistance when chambering the round. just a slight ligh thumb push is all it takes.

according to nato 7.62x51 head space gages.. the 'go' gage closes very easily, the no go gage does not close (just barely) and the field gage also does not close but gets kinda close.

so my chamber now is on the loose side. at the range, i see my brass is covered in marks, like maybe stretch marks, it surely wont be use-able again. and for some reason, the end of the cartridge by the rim, there is a second there about 5mm wide that has no scratches at all or evidence of budging or case trauma.

Herei s an example pic of the cartrige, what is making all roughed up and beat up looking? and why is there no damage ont he last 4-5mm of the cartridge, near the rear part.

http://home.comcast.net/~jcheck10/fal308.jpg

ce
February 14, 2009, 17:23
The brass around the cartridge base is called the web, and it is thicker than the case body, so it does not obturate as the rest of the case does.

Your fireformed case does exhibit some signs of an ample proportioned chamber, or loose headspace, but not inordinately so.

Is this your SAWstock unit, with the open eared gas block?

What kind of ammo?

Is extraction difficult?

Is accuracy acceptable?

Is the bolt real floppy with the action closed? Reach in the mag well and try to move it with your thunb.

You could go to a .257 locking shoulder, but that would be the third installation, and you might get some fatigue in that hole.

Maybe try another bolt with the headspace guages.

twistedneck
February 14, 2009, 20:19
ce, yes, this is the old saw stock rifle. i ordered a 260 shoulder and i was planning to file it down to the proper chamber tightness after placing it in the receiver.

good point about the hole fatigue / wear out. this will be the third time i've put a new shoulder in.

the only thing is, the brass that it ejects can not be reloaded due to the expansion of the case. btw, thanks for describing why the last 5mm of the case does not expand like the rest - did not know it was thicker. I was sure it was somehow supported while the rest of the case was not.

Dilemma, now i have a new LS coming - do i not risk it at all and look for a new bolt and carrier with a tighter head space? OR, do i risk it one more time and put this new LS in?

Finally, it fired great on the range - very accurate, cycled excellent.. is it wrong to have this much brass damage? after all, the 7x62.51 Nato field gage would not close, nor would the regular 7.62x51 NATO 'no go' gage - barely.. but it swallows up the 'go' gage easily when a lot of rifles wont even chamber the 7x62 go gage.

:confused:

Deltaten
February 15, 2009, 09:37
Hmmm...
Taking as fact that the HS gauges in question are truly NATO 7.62 dimensions, it would appear that the HS is within specs. How something can "just barely not close"(sic) is curious. Determining just how much under no-go the HS is, is tough trick to quantify using "thumb pressure".

I use a set of inspection feelers with the extractor removed. They are thin in the width axis and rather long. With a bit of fiddling, I can slip them between the HS gauge and the bolt face via the extractor cut. Barring availability of the same style of feelers; I wonder if some of that automotive"crush" plasti-gauge would be helpful to determine actual HS?

Most of the marks on the brass look typical. The slight bright "ring" at the shoulder is a bit suspect, tho. Prolly from slight elongation of HS**. The general scratches might be from a rough chamber. Easy to fix w/a polishing bob and some rouge.

**A plethora of data is available on ammo spec and HS dimensions. Someone recently surveyed a lot of ammo for actual HS length and found, IIRC, most were fairly short. Figger it out.... "short" ammo and elongated HS will exhibit features such as you have shown.

Given that the gun works properly, is within spec and is accurate; I wouldn't fugk with it! So.. unless yer worried about reloading the sometimes-found brass... no sweat!:D
Not making light of a serious situation; but most guys write about guns not running; usually with tight chambers and close set HS. Check a few fired cases for incipient case separation by lookin/feeling for an internal "ring", as mentioned on other threads.

Best,
Paul

ce
February 15, 2009, 11:24
Yeah that bright ring at the shoulder did indicate stretch, maybe, but run that brass through the sizing die to see how much that stretch is.

You have an Argentine barrel, so the chamber may be rough, or eccentic, given the examples we have seen of late. It may even be chrome lined.

I'm with Paul though, if it works and shoots, so what if the brass gets pounded, as long as it's laying on the ground when yer done, drive on.

You may just open the gas regulator a little to bleed off some pressure, and it might tame the violence of extraction.

Don't file locking shoulders, or you'll start a big argument on the files.