headspace gunsmith question

nitsa216

February 16, 2012 16:12

If a military bolt action rifle ( Arisaka type 99 ) has a miss matched bolt, how do you determine if its safe to fire ( if you don't have a headspace gauge )What are the procedures to check if headspace is OK w/o gauge ?

0

• 

  SoreShoulder

  February 16, 2012 16:42

  I would try a shim on the back of a cartridge.
  
  I have never fired a gun with mildly excessive headspace this way but I am quite convinced you could safely fireform cases to your chamber if you lightly lubed them. Others say lube on a case is dangerous.
  
  In WW2 the navy tried to run its 20mm aerial cannon with wax-lubed cases because they kept coming through with 2mm extra headspace, but I am not aware of how many head separations they had and I don't think the breech of the weapon was in the pilot's face. They tried to switch from .50 but couldn't get enough working cannon together until late in the war.
  
  Don't forget you can test for headspace by firing remotely by wrapping the gun in a towel and tying it to a tire, and pulling the trigger by a string. Just make sure something takes the recoil or you might bend or break the sights as the gun tries to recoil into the towel. Put the buttplate firmly on the inside of the tire.
  
  Then section a case and look for an expansion ring. (You will not find an expansion ring if you lube your case because the entire wall will be able to expand evenly, but then the test means nothing unless you fireform all your cases that way.)
  
  Or you could start with '06 or 8x57 brass and leave the resizing die turned out one turn or more, then turn the sizing die in more and more until the case just chambers. The case head of those rounds is the same as 7.7. You would then lock the lockring on the resizing die and leave it that way for the life of the rifle, maybe by freezing the ring in place with a mark or a dab of epoxy. If you use epoxy you have to use it while the die is in the press or else it will crack when you tighten the die into the press. You should also make sure to get plenty under the threads or it can crack when you loosen the die out of the press.
  
  If you got the 8mm brass you might get away with not having to trim but on the other hand the cases might grow from being squeezed down so much.
  
  However, if you don't have to trim then you couldn't use the crimping shoulder on your seater die because the cases would fall short.

  0
• 

  mrbruce

  February 17, 2012 04:08

  You really should hunt up a headspace gauge to be on the safe side.
  A strip of tape on the head of the case will let you know if it's close or not.
  If 2 pieces of cellophane tape on the rear will allow the bolt to close you have a problem...

  0
• 

  SP45

  February 17, 2012 05:26

  two layers of maksing tape on base. take bolt out and strip. put bolt body back in let handle fall under it's own weight (no pressure). it should not fall all the way to locked position but stop partway down.

  0
• 

  MIKE WISKEY

  February 17, 2012 06:29

  the ONLY real way is to use the proper guage, all else is just guess-work. ALL ammunition is made undersize to fit in ANY chamber, useing shims or tape is, at best, an uneducated guess

  0
• 

  lilmor50

  February 17, 2012 06:31

  i've been fooling with the arisakas for 40 years. tried a dozen or more mis-combinations. NEVER found a seriious headspace problem. the action is extremely strong, only the type 38 is stronger, no record of any catastrophic failurer operator injury. don't worry so much.
  morty

  0
• 

  SoreShoulder

  February 18, 2012 03:51

  You know what, two layers of tape may not provide a precise reading but they will probably tell you if the headspace is safe enough to fire without catastrophe. You can then section a case and see if there is an expansion ring inside, just ahead of the case head (base.) I don't think it will fail if it's that close, even if it's not too precise a test. Then you will know if you can expect to reload and use the gun safely.
  
  The case will not be able to stretch evenly if the chamber and case are free of oil but will stick to the chamber walls when the pressure is high, so excessive headspace would show as a ring of thinned metal just ahead of the base of the case just inside and behind of where the marks left by the chamber on the case end at the back of the case.

  0
• 

  nitsa216

  February 19, 2012 07:11

  yhanks for the input

  0
• 

  nononsense

  February 19, 2012 13:49

  nitsa216,
  
  Now that you've heard from the amateurs and wannabes, here's the correct answer for all situations such as you describe:
  
  Take the complete rifle to a gunsmith and let him gauge the chamber and then examine the whole rifle in its entirety. This is the only safe method to determine what's correct on any given rifle. Period.
  
  Any other concoction is at your own risk.
  
  Best.

  0

Please sign in to leave a comment.