Should I even bother buying a headspace gauge for my AR10?

[little_scrapper]

My LaRue is said to be safe for both 308 and 762. Measuring head to shoulder (0.400" datum). My fireformed brass is coming out mostly at 1.626" but some as long as 1.628".

I measured some M118LR and FGMM 180gr Bergers (I believe) they are. Both measured 1.621-1.622". So both the 308 and NATO seem to be using similar spacing.

*Shrug*

 

[Steel head]

So fired brass is .004 to .006 longer?

 

[little_scrapper]

Yep. Mostly it comes out 1.626 and I bump shoulder .003" to 1.623". +- .001"

 

[Steel head]

That’s not bad for a gasser.
I’d just run it.

 

[little_scrapper]

Just started reloading so i am trying to figure out if the rifle is capable of any real precision. Can I find a load that will shoot consistently under 1MOA. Newb as I am I can shoot .7MOA with my ar15 but thats a different animal.

 

[Ryridesmotox]

Find a bullet and powder that your barrel likes, you'll be good to go. I like IMR4064, but varget, 4895, 8202xbr, and a bunch of others are also quite good. Try some 168 or 175 sierra match kings. I like the regular, not the tipped ones personally, but your mileage may vary on that.

As far as 308/7.62Nato, pick a head stamp and try to prep everything the same. When I first started reloading, I found a dude that left like 200 cases of 308 PMC brass at the range. I picked those cases up and loaded with them for a year before I went and actually bought high quality brass.

 

[Howland]

My understanding is the spec difference between .308 Win and 7.62 NATO is the dimension of the leade, not headspace. I would think resizing to factory dimension with a 0.007" difference will eventually lead to case head separation.

There is still a need for the headspace comparator but the AR platform makes it easy.

Measure once fired brass and sort to find the longest headspace case. Size it with the die backed out a bit to be sure you aren't bumping the shoulder back. Remove the upper, slide the case rim under the extractor, keep the case aligned with one finger while sliding the BCG forward with just light finger pressure. If it goes to bolt lockup, case headspace is still less than chamber headspace. It may take several firings.

Once you find a case that won't go to bolt lockup with light finger pressure, measure headspace. Keep resizing and rechecking, turning the die down a little each time. With standard thread dies each 5° turn sets headspace back almost exactly 0.001".

Repeat until that longest case locks up with just light finger pressure.

That sizing die in that press with that shellholder is now perfectly adjusted for that rifle chamber. Extraction will beat up your brass long before you have case head separation.