300 Blk AR headspace

[gbw]

Probably should have thought of this sooner...

I recently bought an Anderson AR 15 upper with installed 300 Blk barrel, no BCG, from Brownell's.

I also got from Brownell's, separately, an 'M16 B-Tac' complete BCG, and charging handle.

All of the parts look very good, completed upper hand cycles butter smooth.

The question is whether the upper is shootable as-is, or is headspace checking/setting needed first?

Thanks, gb

 

[redbullitt]

Honestly probably best to always check... better safe than sorry. I doubt a visual inspection could catch an issue like that, at least not mine unless its a huge problem.

 

[Walkalong]

While your chances are extremely good everything is fine, it never hurts to check. You could buy a go and a no go gauge, or pay a gun smith to check it.

 

[hdwhit]

I think anyone building a rifle should ALWAYS invest in a set of Go/No Go headspace guages.

 

[Tirod]

It's usually recommended to check headspace, and then, on the other hand, tens of thousands of AR's get put together at home and shot no checking at all.

How is that possible?

The AR is uniquely different from most all other firearms. It does not have a barrel which is set into a receiver and which has a bolt which also locks into a receiver. That older form of firearms manufacture requires headspace checking because that bolt, receiver and barrel aren't capable of being set previously, or to any known standard. The first time they go together is the first time they can be checked.

The AR has a barrel extension which screws onto the barrel - major difference. When that is done at the factory by the assembly line tech he then checks the headspace as the next step - the barrel extension is the part the bolt locks into, therefore it can be checked right then and the headspace adjusted to specifications. In point of fact, that is the only way it can be done, as the barrel extension is then pinned in place, the barrel oriented to put the feed ramps in the extension down, then the gas port drilled in the correct vertical location. Once that is completed the extension cannot be adjusted further as it would orient the gas port out of vertical, requiring a new port location.

All AR15 barrels with the extension installed are already headspaced. That is the large majority of them available. Therefore the aftermarket builder buys a milspec bolt, finishes assembly, and goes to the range, where they carefully examine the first shot casing for signs of distress.

Is there a chance of this not working for somebody? Yes, and it does exist, but its pretty small. And what do they do about it if they find headspace is out of tolerance? They buy a dozen bolts and keep checking until one fits - which is expensive or they pay a gunsmith to fix it and then he's left to plug the old gas port and redrill a new one. Both cost more than the barrel assembly - so the preferred solution is to return the barrel unfired under warranty to the manufacturer and get a new one. However, that is going to also cost the builder a set of gauges at the very least - and the use of them some professional instruction to have some credibility with the maker. They will double check it and can claim it's ok.

It has to be said that the number of guage sets available on the market has expanded tremendously in the last five years and that alone can bring them into question, too. Who built them, is that maker credible, and how reputable are they on the market? Nobody knows much about those guys, you have to trust who's selling them as a second hand recommendation.

It stacks up to comparing a known barrel maker vs an unknown gauge maker being used by an untrained assembler. It's not rocket science but I can't tell you the number of times I've had people come into the auto parts stores claiming a certain part was causing an issue - and they not only hadn't tested it, they had yet to raise the hood on the vehicle. And they don't even own a ohm meter or a set of cheap digital calipers or a spark plug wrench.

We get a lot of that with firearms, too. But, the customer is always right, so you have at least that reassurance even tho the idea that something is wrong might be wrong itself. And the cash registers keep ringing.

 

[gbw]

I'm pretty much in agreement with Tirod on this. NORMALLY, headspace must be checked and adjusted. For non-AR type rifles, most barrels are sold short-chambered for just this purpose - the chamber must be finished-reamed and headspace verified after final assembly. You better know what you're doing.

But in this case the following apply also:
The Upper and Barrel were assembled at Anderson Mfg, and purchased from Brownell's. The likelihood of HS being not set correctly is minuscule. Likewise the bolt is from Brownells, and they DO NOT make a habit of selling out-of-spec parts.

I have now shot the rifle, very accurate, smooth cycling, and so far reliable. Brass looks fine. (I did shoot the first 5 rds. with protection, then examined the cases carefully). The only 'gunsmithing' I did on this rifle was to use a diamond stick to break sharp edges and a couple small tool marks on the BCG.

Regarding Brownell's, for those who don't know them. For gunsmithing tools and parts, it's true they are somewhat expensive. But imo they are well worth it.

For the 30 plus years I've dealt with them they've shown they actually care about the business they are in (guns and gunsmithing), high quality, and their customers. I've had reason to see this many many times over the past 30 years.

Their guarantee is absolutely unmatched. They will replace or refund anything they sell for free. No questions asked. I've used it several times in the past and they have never cared if part/tool was unused or if you've used it or installed it.

• I returned a special 1911 file once after using it 3 years, it dulled before it should have. It wasn't cheap. Replaced immediately free.
• I also once returned a 1911 hammer that broke (a premium hammer) that I had modified and used for a year. I told them I'd worked on it, they didn't care. Replaced for free.
• Returned an unused Kart NM barrel I ran across after 5 years, as soon as they could figure out what I paid for it, immediate refund.

I have no interest in Brownell's except as a very very happy customer. If I need a part or tool I need to be safe and dependable, I use Brownell's.