Ar-15 headspace

upstate88 · Nov 13, 2018

If I am using a quality barrel and BCG do I still need to buy gauges? And second question If I have an upper in 5.56 and one in 6.8 spc, should I just be able to swap out the bolt and use the same BCG?

I get that these are kind of loaded questions, but I am looking for folks who have built some ARs who may have some headspace and swapping experience.

Unka-Boo · Nov 13, 2018

If using new quality parts, you should be fine. BUT, it doesnt hurt to check. With bolt groups as cheap as they are now, it doesnt make sense to "share" a carrier....( but you could )

Rule of thumb I was taught:

new bbl-new bolt= good to go

new bbl-used bolt= might be ok, check with gauge

old bbl-new bolt= same as above

old-old....dont bother

DirectDrive · Nov 13, 2018

upstate88 said:
If I am using a quality barrel and BCG do I still need to buy gauges?

With the AR you can get away without checking headspace as the end user when using quality components.
If you're worried you can...

1) Buy a barrel with a matched bolt
2) Buy buy the Colt II Field Gauge (1.4736")
3) Buy the kit

I bought the Field Gauge and used that for my first build.
Later builds I did not check.

And second question If I have an upper in 5.56 and one in 6.8 spc, should I just be able to swap out the bolt and use the same BCG?

You swap out the bolt and use the same CARRIER.
BCG means Bolt/Carrier Group.
Also with 6.8SPC you will need 6.8SPC mags and 6.8SPC barrel.

To recap :
6.8SPC requires...

1) 6.8SPC barrel
2) 6.8SPC bolt
3) 6.8SPC magazine

upstate88 · Nov 13, 2018

Misspoke on the BCG thing. I was more asking if swapping the bolt back and forth was a bad(lazy/cheap) idea.

808hondacrguy · Nov 13, 2018

I had a LGS that used to check headspace for me at no charge, and out of MANY builds, never had a no go. They have since gone out of business, and I have not checked headspace on any builds since.