Real or ?

Quote:

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Originally Posted by limpetmine

Mine is extremely hard on the close. It's like it's got a bolt head fitted that is 3 sizes to long. I've not checked it yet, as there are others to shoot.....
(Brian, I need some guages, too!)
Now, the No.4 Conv. shoots sweet, and the adjustable diopter is just the ticket.

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Limpetmine

Normally the unfired cartridge case is made approximately .002 (two thousandths) shorter than the minimum headspace setting for a given rifle. The L39/L42 minimum headspace is .002 tighter or shorter than SAAMI or American military 7.62 NATO.

You can use a RCBS Precision Mic to measure your cartridge case before and after firing to check “cartridge headspace” or how long your case is.

https://www.milsurps.com/images/impo...MGP51301-1.jpg

Below is minimum or “zero” headspace 1.630 for the .308 and American 7.62 NATO.
(Minimum headspace for the L39/L42 is 1.628)

https://www.milsurps.com/images/impo...MGP51571-1.jpg

Below a European surplus 7.62 NATO loaded cartridge that is only ½ thousandths shorter than SAAMI and U.S. military standards AND 1 ½ thousandths longer than L39/L42 minimum headspace.

https://www.milsurps.com/images/impo...IMGP5256-1.jpg

Below a commercially loaded Winchester .308 cartridge and it is .002 shorter than minimum SAAMI and U.S. Military headspace of 1.630

https://www.milsurps.com/images/impo...IMGP5254-1.jpg

NOTE: Reloading manuals warn you to NEVER shoot reloaded cases that were used for reduced loads again for full power hunting loads, example using reduced pistol or shotgun powder charges for low velocity plinking loads.

The reason for this is because the cartridge case gets shorter each time it is fired because the force of the firing pin hitting the primer actually makes the case shorter. (you will end up with excessive headspace or head gap clearance and have case head separations)

Now with the RCBS Precision Mic an unfired case and a fired spent primer and by dry firing this empty case and then remeasuring the case you can find out what headspace measurement your bolt closes normally without the rear of the case touching the boltface.

Your hard chambering ammunition may not meet British 7.62 ammunition standards and is causing the hard closing of your bolt.

The only thing standard with 7.62 NATO ammunition and the countries that manufacture this ammunition are the numbers “7.62”.

Signed
The excessive compulsive headspace fanatic. :rolleyes:

Ed, the very last paragraph above is SO true! 7.62mm NATO is a wierd and wonderful thing. We had the unfortunate experience of being lumbered with a whole load of 7.62mm NATO ammo from Nigeria............ well, I say Nigeria because the ends of the boxes were painted in a green/white/green flash, as in the Nigeria flag but I suppose it could have been anywhere really, but they got the blame. You know, Nigeria being a prominent NATO member and all that! Some of this stuff was full of dynamite that sent the Bren cases crashing into the gravel of the firing point with such force that the gravel was flying up/back at the same velocity as the bullet while other stuff was full of talcum powder that wouldn't pull you off the nest.

It was all we had so we used it and the Ammo Tech boys told us afterwards that we were imagining it because it was all NATO standard. Bless 'em.............. I pulled this dozy Sergeant aside and asked him how long his ammo tech's course had been then told him how long I'd done at Uni. Then he explained it away because I didn't have my finger on the pulse with regards the weapons....., Bren guns! You know what it's like when you really want to give someone a good slapping................?

Ah, yes....., 7.62mm NATO

Each country that belongs to NATO and also manufactures their own 7.62 NATO rifles also designs their own chamber dimensions, headspace dimensions and ammunition dimensions.

The British L39/L42 has tighter head space settings than the L1A1

L39/L42 1.628 GO 1.635 NO-GO
L1A1 1.6352 GO 1.643 NO-GO

U.S. M14 1.6355GO, 1.6455 FIELD REJECT
SAAMI 1.630 GO, 1.634 NO GO, 1.638 FIELD REJECT

Then we have NATO and SAAMI cartridge headspace standards (case headspace length)

7.62x51mm NATO minimum cartridge headspace 1.630
7.62x51mm NATO maximum cartridge headspace 1.633
7.62x51mm NATO average cartridge headspace 1.6315

.308 Winchester minimum cartridge headspace 1.627
.308 Winchester maximum cartridge headspace 1.633
.308 Winchester average cartridge headspace 1.630

Limpetmine’s L39/L42 problem could just be trying to chamber NATO ammunition that has a cartridge headspace length of 1.633 in a chamber that is 1.628 long. (the case is .005 longer than his chamber)

Limpetmine, you might have to call Hunts Tomatoes and find out how they get those eight big tomatoes in that little bitty can. :D

Could you write all that down on a big long hardwood stick, about 2" in diameter and next time I see the ammo tech, I'll suggest that he, er, sticks it......, er......, somewhere useful..............