[Luke]

I thought I remember reading somewhere that the .308 round and the 7.62X51 Nato cartridge dimensions are slightly different. Centerfire is sending me my M53(Mg42 type) gun and I have the conversion parts to turn it into a MG3. I have heard(which makes a lot of sense) that it is critical to make sure your bolt and 7.62X51 barrel headspace properly with each other(I always prefer to be safe). So my question is on my Brownell's catalog they only sell the .308 go and no/go gages, is it OK to use these, if not who sells the Nato 7.62X51 spec gages? I also plan on checking my extra 8mm barrels that I have with my 8mm gages.

 

[hagar]

The .308 gauges you have will work just fine. I have built many rifles in 7.62 with .308 gauges and none have had any problems.

However every military 7.62 that was factory built has always headspaced on the .308 no/go gauge rather than the go/ gauge. At least I have found this to be the case for me. I don't know for certain why this is but I believe it might be due to the full auto capability as metal expands when it is heated and I would think if the headspace was tighter on the go gauge the weapon might freeze up under continuous fire. The one exception to this I have found are the match rifles and they also take special gauges but they are fitted to very close tolerances.

 

[GS-Patton]

I need to get a headspace gauge for my 1919, I have one for an M14/M21/M60, I was hoping I could use it on my 1919 but after lookin the tutorial over on here they dont even look the same

 

[Luke]

Hagar, what your saying makes sense because too tight headspace might cause the bolt to release the firing pin when the bolt was not fully closed(whereas a bolt action you know you closed the bolt and the fouling issue become a non-factor because your round expenditure is very low). Needless to say a cartridge not fully seated will cause the barrel to fly out of the side door and maybe lead to injury beside definite gun damage). I've built many other types of guns but none in these calibers and I realize there is a learning curve involved so thank you all for your input.

 

[overbore]

Chamber

for the Nato spec is 0.010" longer that the 308 Win which 'splains the no go gauge working for the 1919.