Anyone for 7.62mm CHS?
Posted By: Peter Laidlericon
Date: Tues 6 May 2008 11:36 am
Now for the biggie, the 7.62’s. The basic principle of headspacing hasn’t changed here but the practicalities have. Whereas before, on our rimmed .303” rifles we measured the GO NO-GO distance between the front face of the bolt and the rear face of the barrel, it’s all changed for the rimless 7.62mm NATO caliber rifles. Now we have to measure from the front face of the bolt to the cartridge seating at the neck. Well, that’s all pretty clear then ….., except that the neck is tapered so where EXACTLY on that neck do you take your GO, 1.628” and NO-GO 1.635 measurement from? Even if I told you it’d make no difference whatsoever because without the specialist measuring and more importantly, the calibration equipment, you’d still be none the wiser. The trouble with this is that you’ve got to take the word of the manufacturer of the gauge. And exactly where does HE take HIS measurement from but more importantly, WHO does he get them from. geting difficult isn't it?
Let me give you an example. My GO gauge gives you a close/GO reading of 1.628 but Bloggs & Co gauge may give you a GO reading of 1.575” for the same 7.62mm caliber. How can there be a difference of .053” between the two when they are identical? Well, it’s simple really. Our STANAG gauges are measured from one diameter around the neck while Bloggs & Co are taken from a different but larger diameter .053” further to the rear! That is really all I want to say about that.
The next obvious question for all you enthusiasts is where can I get a set of these gauges and the true answer is that I don’t know! But here’s what I propose. If you HAVE a set of spurious/said to be/reported to be/hope they are 7.62mm headspace gauges, I will calibrate them for you and tell you EXACTLY what it is you have. The fact remains that there are MANY gauges for all manner of 7.62mm rifles and machine guns ranging from the little bolt action L8’s right through to the L- whatever it is ferocious mini gun. And there are equally MANY for different lines of repair and functions, ranging from 1.622” to 1.648”.
Once I return them, calibrated, at least YOU know that if the ‘unknown’ gauge you sent to me to be calibrated comes back as a STANAG calibrated 1.6325 gauge (GO for the L1A1 rifle incidental.....) then it will suffice as a NO GO gauge with your 7.62mm Enfield provided that you slide a sliver of .003” steel shim across the bolt face first, on the basis that 1.632 plus .003 equals 1.635.
On the other hand, if you’re clever, you COULD just have the rear face ground down by .0045” to end up with a 1.628” GO gauge.
That just about covers the 7.62mm versions. The question of calibrating your gauges is one that needs to be looked into by ‘some friends’ on both sides of the pond. I can see already that this is about to open up a whole new can of worms...... But just hang on in there....................