AR15 Upper + Lower. Do I Need to Headspace?

[HGM22]

Quick question: if I buy a complete upper and either build/buy a complete lower, do i need to headspace the rifle?

What if the upper doesn't come with a BCG and I add one later from a different manufacturer?

 

[redneck2]

Short answer, no. Snap 'em together and run.

When I was snowed in for five days straight, I was doing the Google/Youtube thing to kill time. Ran across some really good videos about building uppers and lowers. I've helped build lowers, but didn't really understand building an upper. The clip was about 25 min long IIRC and very well worth it.

After watching it, I'm getting torqued up to build an upper.

 

[nastynatesfish]

Ya asking as your not buyin a barrel blank with out te extension your good. You could check it for your own well being if you wanted. When I buy a used upper ill prime a sized trimmed case, chamber it and put the muzzle to a cloth on the floor and fire it. Just to check te case out. Not enough pressure for any sort of failure but you can still get a pretty good look at chamber dimensions. If a new upper from even a half decent source, just pin it and shoot

 

[nastynatesfish]

ARs are net run to as close tolerances as bolts. Since you don't have the canning action of a bolt to chamber you will have some space on your new bcg. Not excessive but some. That's why brass fired from full auto weapons has te web stretched and sizes a lot harder that same brass in a bolt. IMO

 

[Monkeybear]

It's one of those deals where I find it hard to argue either way. On one hand parts from a good manufacturer should be in spec and LOTS of people build ARs every day without the aid of go/no go guages. On the other hand with a little effort you can probably find a shop that will headspace for you and it shouldn't cost much at all.

While for 99.9% ARs its not an issue when its yours with the problem that .01 might as well be 100 so if someone asked me I would say just get it checked. That said, if they didn't want to I probably wouldn't argue with them.

 

[pintler]

Just to be clear: AR headspacing is determined by the bolt and the barrel/barrel extension assembly.

The upper, lower, bolt carrier, etc don't matter - only that trio of parts.

I think it would be unusual for a new bolt and barrel/barrel extension from reputable maker to be out of spec, but you could get unlucky. If the barrel/extension or bolt are used, I'd check. Heck, I check headspace even for new parts unless they were sold as a unit, e.g. a new complete upper or rifle, or matched bolt/barrel assembly, but I admit that's being pretty conservative.

 

[carbine85]

No. A properly built upper should be ready to run. It has nothing to do with the lower.

 

[Walkalong]

Here's a recent thread about it.

http://www.thehighroad.org/showthread.php?t=741319&highlight=go+no+go

 

[SilverCat]

No. But be sure to always headspace a custom upper. If it isn't spaced correctly, you've likely got a bad barrel.

 

[hentown]

I've built a bunch of ARs. Never checked the headspace of any of them. They all work great. If you buy a barrel with the extension attached, it'll have been headspace.

The lower has nothing to do with headspace.

 

[Quentin]

Just to be clear: AR headspacing is determined by the bolt and the barrel/barrel extension assembly.

The upper, lower, bolt carrier, etc don't matter - only that trio of parts.

I think it would be unusual for a new bolt and barrel/barrel extension from reputable maker to be out of spec, but you could get unlucky. If the barrel/extension or bolt are used, I'd check. Heck, I check headspace even for new parts unless they were sold as a unit, e.g. a new complete upper or rifle, or matched bolt/barrel assembly, but I admit that's being pretty conservative.

I agree, if you have a quality barrel/extension and bolt (BCG) and they are new then they should headspace properly nearly 100% of the time. Still, why not take the time to check and be sure, why be that one that falls in to the bad >1%.