AR15: Headspacing needed for replacing factory bolt? (Read 3486 times)

PalisadesKid

AR15: Headspacing needed for replacing factory bolt?
« on: March 08, 2017, 10:44:38 PM »
Personally, Im anal about having spare factory parts for all my guns just in case. Got a Colt 6721 and Brownells and Midway USA has spare Colt factory .223 Bolts.

Wondering if headspacing is needed for replacing this factory part. Everything on the rifle is factory, no aftermarket barrel extensions, barrel, nothing. Its all from the factory.

Surf

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #1 on: March 09, 2017, 06:24:04 AM »
Generally the answer is no need for headspacing.  On the AR/M4/M16, if you use quality parts from a known manufacturer that are truly made and tested within MILSPEC dimensions, they are 99 plus percent compatible.  If you are using a factory Colt bolt in a factory Colt barrel with factory Colt barrel extension the compatibility is pretty much assured.  Keep in mind however that if you want extreme precision matching a bolt to a barrel and its extension within a certain tolerance is a good thing. 

drck1000

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #2 on: March 09, 2017, 08:35:46 AM »
What Surf mentioned is my understanding of the issue.  That said, I'm not really into building ARs personally, but you've gotten feedback from someone who is and has. 

If you are REALLY anal or just simply curious, I have a USGI field gauge if you want to borrow.  I bought it a while ago and never really used it.  I hope I can still find it.  Haha

Sounds like you've got a factory upper and are concerned/curious about using a different bolt or even BCG.  I've swapped bolts and BCGs a bunch of times.  It was all quality parts (bolts and BCGs) from known manufacturers and factory assembled uppers, even when combining different manufacturers.  For example, an LMT upper with BCM BCG. 

At one point, I was interested in putting together an AR upper that was intended for more precision shooting and was looking into headspacing, but that never got off the ground.

Flapp_Jackson

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #3 on: March 09, 2017, 09:11:20 AM »
I have built 3 AR-15s.  One had a complete upper, which I took apart later and changed the front sight /  gas block and handguard to free-float the barrel.  The other 2 I built from parts I ordered or found locally.

No problems at all with headspacing. From what I've read, even if you have problems, there isn't much you can do to fix it other than use a different bolt which is assuming that's the part that's the issue.

I stay away from the "$49 BCG Super Discount" ads.  I buy from retailers and manufacturers who check each part for quality control.  MILSPEC is the key.

Having said that, it's like a safety inspection for the car.  You might pass every time you inspect a relatively new car, but one day you fail from a broken wiper or worn tires you failed to notice.  Having the gauges and periodically checking will potentially catch a problem before a part fails.

Brownell's sells a Go/No-Go pair of gauges for $65 for 5.56 NATO.  They also sell Match-quality gauges (though most are out of stock) from Forster:  Go / No-Go / Field.  Each run about $30 and are recommended especially for building a match-quality rifle.

If your barrel is marked .223, use those gauges.  If marked 5.56, use those. 

The real problem comes when you randomly get a barrel and extension that's maybe at the maximum threshold limit for tolerance, and the bolt is at the minimum threshold.  I've seen this referred to as "tolerance stacking," where the combination of variances, still within spec but in opposite directions, makes the difference between the parts being "close enough" and causing problems.

« Last Edit: March 09, 2017, 10:37:37 AM by Flapp_Jackson »
"How can you diagnose someone with an obsessive-compulsive disorder
and then act as though I had some choice about barging in?"
-- Melvin Udall

changemyoil66

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #4 on: March 09, 2017, 09:25:46 AM »
Perfect timing.  My wife is almost done with her 1st build.  She got a 223 Wylde barrel spiral fluted, and was looking at BCG's.  We were told about the head space probable issue.

Still shopping for a BCG. 

PalisadesKid

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #5 on: March 09, 2017, 10:17:56 AM »
Mahalo guys!

Surf

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #6 on: March 09, 2017, 05:25:44 PM »
To add, you will find more out of spec chambers in poor barrels / extensions from lesser quality manufacturers.  Not as much of a concern from Colt at this moment.

whynow?

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #7 on: March 09, 2017, 10:19:58 PM »
As the others replied, a new bolt in your factory Colt upper shouldn't cause headspace issues.  But I would still get go/no-go gages.

aaronc5362

Re: AR15: Headspacing needed for replacing factory bolt?
« Reply #8 on: March 10, 2017, 05:43:54 PM »
I agree that it shouldn't be a problem but lemons do happen so, headspacing is just good to do once in a while. If your in a rush and need to do ASAP cause you wanna fire it tomorrow and don't have gauges. Have 2 rounds available. Whether home made snap caps or whatever. Also strip ejector and extractor on both bolts. Reinsert oem bolt since you know it works.

1. Since you have a reliable bolt already, measure OAL of a bullet, put a piece of tape on the primer end or bolt face and insert the round. (If you reload just don't add primer or powder. I had a spare firing pin that I shaved down so there is no perstrusion . I use that and live rounds when I function test. And selector on safety. And I face it in a box full of old newspaper and telephone books. My box is about 3x4 feet. And I hold it by my dominant hand behind the trigger shoe. No possible way it could go off *shrugs* So no slam fire if that's an concern.) then check if bolt locks in. Do it until bolt doesn't lock. Count the amount of tape needed.

2. Repeat same procedure with new factory bolt.

3. Be safe lol!. my shaved pin is clearly a different color so I can't fuck up. And I always triple check before doing so. Just be cautious and smart.

Cheap/ quick  way, for just a test. Keep in mind, if you decide to shoot tens of thousands of rounds on your oem bolt, and decide to use new bolt, the headspacing now may be different down the road. Could be an issue in the future. Throat erosion or whatever.

When you have funds or time, should get no go an go gauges as I did.

Good luck and be safe with my 2 cents.