Headspace Question

[SOTAR]

Is disassemble of the bolt (removal of the ejector) required to properly check headspace using the go and field gages? Particularly the Brownells gages?

I say it's necessary to disassemble the bolt to check headspace. The brownells field gauge is a Forster product. I will admit that it can be a pain if you don't have experience dealing with the ejector roll/spring pin.

All of my gauges are modified so bolt disassembly isn't required. When a bolt/barrel combo fails, I always follow up with other gauges to verify my gauge is not off. I also check the calibration on my gauges every 6 months.

[SOTAR]

Of course the correct answer is that you should check headspace.

On the flip side, is there evidence of catastrophic failures caused by improper AR-15 headspacing?

If the barrel and bolt are manufactured to spec (aka quality components) the the worst case would be having both at the minimum or maximum amount of tolerance. If the headspacing is slightly short, pressure would theoretically be higher and if slightly long, brass life will suffer for reloaders.

If headspace is drastically short, the bolt won't close on a live round, if drastically long, cases could separate (headspace would have to be ridiculously long). Case separation can absolutely cause catastrophic failures.

I have seen plenty of pics of ARs that suffered catastrophic failures due to out of spec loading/ammo but none blamed on headspacing.

Note that my post only applies to .556/.223 AR-15s.

Andy

I have experience with AR's that have kaboomed that had short headspace. I checked them and warned the owners before the guns blew up. Sometimes there were often additional issues present that lead to the blown up gun. Ammunition can sometimes be the sole cause as well.

Diagnosing a kaboomed gun afterwards can be impossible in some cases depending on how the parts were damaged. Being conclusive about tolerances with bent and broken parts is often a futile effort. I have experienced success in proving it out in a few cases.

Short headspace can cause reliability issues when the gun gets hot or fouled. It can have extraction issues and failures to go into battery. Not all ammunition is loaded to the same dimensions or pressures so some ammo won't show a problem, and other ammo will. The point of using headspace, throat, and chamber gauges is to ensure the gun will function with a wide diet of factory loaded ammunition. It also ensures the gun will run hot, cold, wet, dry, and so on.

Short headspace can also lead to accuracy issues with some ammo, primer popping, bolt face etching, destroyed brass, and can increase the chances of bolt lug or cam pin hole failures.

Many people assume that a certain brand ensures a part is in tolerance. They fail to understand that the AR is a "recipe" and all the parts are supposed to work as a system. How those parts interface is more important than individual dimensions of a part. Two parts can be made within the plus or minus and still be good, but when mated don't work right or gauge out. This is a tolerance stack issue that people swear won't happen with "quality parts". I see it every day. Why is that? Because I check.

Or you can just run it and hope for the best like many people do.

I'm fine if people don't follow my advice. It's their gun to do what they want.

Im not directing this comment at you, but I'm honestly surprised that members of this well respected forum parrot the same "good enough" advice that other less respectable places do.

[Pressingonward]

I suggest you remove the ejector and extractor from the bolt before checking headspace on any rifle or carbine. The pressure from the ejector may have an affect on your sense of feel while applying pressure against the bolt. Removing the parts gives you an opportunity to closely inspect machined surfaces and thoroughly clean the bolt. I highly recommend thoroughly cleaning the chamber before checking headspace, so you don't get a false reading.

It doesn't take much pressure on the bolt to get a good headspace reading. I've seen a few headspace gauges wrecked when people used them to check headspace on a fully assembled rifle.

I'm having trouble picturing how a headspace gauge can get wrecked when used on a fully assembled rifle - can you explain further? Thanks!

[Whalstib]

Thanks!

I assume companies like Daniel Defense and BCM use in house manufacture of ALL parts and have have mills set up and calibrated to match.

So while a BCM BCG may work fine with a DD barrel perhaps a DD BCG would be a better starting point....

Obviously the problem is multiplied when buying parts from different manufacturers over time. Even if high quality slight variance could stack up to problems....

W

[SOTAR]

I'm having trouble picturing how a headspace gauge can get wrecked when used on a fully assembled rifle - can you explain further? Thanks!

The ejector or extractor can raise a burr on the gauge when you force the bolt into battery. That can make the gauge read incorrectly.

The ejector can load the gauge so it reads incorrectly.

If the extractor cutout (the groove that grabs the rim of the casing) is located incorrectly it can give a false headspace reading.

Using gauges in a dirty gun can also wreck gauges.

[SOTAR]

Thanks!

I assume companies like Daniel Defense and BCM use in house manufacture of ALL parts and have have mills set up and calibrated to match.

So while a BCM BCG may work fine with a DD barrel perhaps a DD BCG would be a better starting point....

Obviously the problem is multiplied when buying parts from different manufacturers over time. Even if high quality slight variance could stack up to problems....

W

It is a safer gamble to follow that philosophy, but it's not a guarantee you won't have a problem. I see factory uppers and complete guns that fail headspace all the time.

Some companies will act fast to remedy the issue, while others just tell you headspace isn't important and to just cram ammo into the chamber and "run it".

[prepare]

I say it's necessary to disassemble the bolt to check headspace. The brownells field gauge is a Forster product. I will admit that it can be a pain if you don't have experience dealing with the ejector roll/spring pin.

All of my gauges are modified so bolt disassembly isn't required. When a bolt/barrel combo fails, I always follow up with other gauges to verify my gauge is not off. I also check the calibration on my gauges every 6 months.

What about these gauges, are they the correct measurements? They're also ground off on one edge[ATTACH=CONFIG]

[SOTAR]

What about these gauges, are they the correct measurements? They're also ground off on one edge[ATTACH=CONFIG]

I can't see the picture.

[prepare]

I can't see the picture.

Click on it.
For some reason;
The go is a--- 1.4636 instead of 1.4646
The No go is- 1.4696 instead of 1.4736

[AndyLate]

I have experience with AR's that have kaboomed that had short headspace. I checked them and warned the owners before the guns blew up. Sometimes there were often additional issues present that lead to the blown up gun. Ammunition can sometimes be the sole cause as well.

Diagnosing a kaboomed gun afterwards can be impossible in some cases depending on how the parts were damaged. Being conclusive about tolerances with bent and broken parts is often a futile effort. I have experienced success in proving it out in a few cases.

Short headspace can cause reliability issues when the gun gets hot or fouled. It can have extraction issues and failures to go into battery. Not all ammunition is loaded to the same dimensions or pressures so some ammo won't show a problem, and other ammo will. The point of using headspace, throat, and chamber gauges is to ensure the gun will function with a wide diet of factory loaded ammunition. It also ensures the gun will run hot, cold, wet, dry, and so on.

Short headspace can also lead to accuracy issues with some ammo, primer popping, bolt face etching, destroyed brass, and can increase the chances of bolt lug or cam pin hole failures.

Many people assume that a certain brand ensures a part is in tolerance. They fail to understand that the AR is a "recipe" and all the parts are supposed to work as a system. How those parts interface is more important than individual dimensions of a part. Two parts can be made within the plus or minus and still be good, but when mated don't work right or gauge out. This is a tolerance stack issue that people swear won't happen with "quality parts". I see it every day. Why is that? Because I check.

Or you can just run it and hope for the best like many people do.

I'm fine if people don't follow my advice. It's their gun to do what they want.

Im not directing this comment at you, but I'm honestly surprised that members of this well respected forum parrot the same "good enough" advice that other less respectable places do.

Thank you for the information. I understand forensic examination after the failure is difficult.

With all due respect, you are introducing additional variables, particularly throat and chamber dimensions. Neither is checked with a head space gauge.

You are certainly not directing your post at me, the first thing I typed was that headspace should always be checked. That's hardly parroting "good enough".

Andy