How is AR barrel measured and permanently attached?

[BSA1]

How is the barrel length for the AR measured?

Or most importantly how does the BATF measure the barrel?

Unassembled?

Simply measure from the front of the collar that fits into the receiver to the muzzle?

Or to the front of a flash suppressor if permanently attached?

After assembly into the receiver?

The Barrel Nut and the Delta Ring will affect the measurement.

Rifles are traditionally measured assembled from the front of the muzzle to the front of the receiver. With the AR it is more difficult to get a measurement.

The reason I am asking is I am considering a carbine build using approximately 14.5" - 14.?" rifled barrel and a flash suppressor to get past the magical 16" to avoid a SBR. (Goal is 16.1" to keep the big bad wolf away).

 

[Cannibul]

I find a tape measure works quite well.



















It's my understanding it's measured from the bolt face to the end of the muzzle.

 

[Telekinesis]

The "official" way to measure a barrel length is to close the bolt and drop a rod down the barrel. So you are measuring from the bolt face to the end of the barrel. If the flash hider is permanently attached (silver solder, or by other means) it can count towards the total length of the barrel.

 

[GBExpat]

The "official" way to measure a barrel length is to close the bolt and drop a rod down the barrel. So you are measuring from the bolt face to the end of the barrel. If the flash hider is permanently attached (silver solder, or by other means) it can count towards the total length of the barrel.

This.

 

[BSA1]

I find a tape measure works quite well.

Except the BATF doesn't use a tape measure.

How about a serious reply?

 

[rbernie]

Post #3 is the correct reply.

 

[BSA1]

So completely assemble the gun.

Close bolt on empty chamber.

Drop rod into the barrel until it hits the face of the bolt.

Mark measurement at end of muzzle / permanently attached flash suppressor.

 

[BSA1]

Follow Up Question

What is considered to be "permanently attached" flash suppressor?

Must it be soldered, brazed or welded to the barrel?

What about red locktite or similar binding agent?

 

[Reloadron]

So completely assemble the gun.

Close bolt on empty chamber.

Drop rod into the barrel until it hits the face of the bolt.

Mark measurement at end of muzzle / permanently attached flash suppressor.

Yes, that would be it.

Permanently attached or fake flash suppressor are those welded or permanently attached to the barrel.

Ron

 

[badkarmamib]

Flash hiders must be soldered with silver solder, welded completely around, or blind pinned and then welded over the pin, to be considered "permanent". If it ever comes into question, their method for determining if you did it correctly is: Place upper in a vise, put a pipe wrench on the flash hider, and go to town. If the flash hider comes off, you go to jail. If your barrel twists first, they give you back your ruined barrel. At least that is my understanding, but I can't find the link to back it up...

"The ATF procedure for measuring barrel length is to measure from the closed bolt (or breech-face) to
the furthermost end of the barrel or permanently attached muzzle device. Permanent methods of
attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver
soldering, or blind pinning with the pin head welded over. Barrels are measured by inserting a dowel rod
into the barrel until the rod stops against the bolt or breech-face. The rod is then marked at the
furthermost end of the barrel or permanently attached muzzle device, withdrawn from the barrel, and
measured."

https://www.atf.gov/firearms/docs/atf-national-firearms-act-handbook-chapter-2/download

 

[Kp321]

Red Locktite is not an acceptable "permanent" attachment method. Even soft solder is not good enough, it must be at least high temperature silver solder, better yet, pinned and welded.

 

[adcoch1]

What is considered to be "permanently attached" flash suppressor?

Must it be soldered, brazed or welded to the barrel?

What about red locktite or similar binding agent?

The attachment has to be permanent such as welding or blind pinning. Locktite isn't considered permanent. It should require machine work or a torch to remove it or it isn't permanent. I can't find the link but there is a BATF decision letter on this somewhere...

Sent from my LGLS740 using Tapatalk

 

[BSA1]

Thanks everyone for the replies. They answer my questions.

I just need to figure out how I am going to get the flash suppressor attached.

 

[badkarmamib]

Probably the easiest DIY I have heard was to drill a hole in the bottom of the flash hider, and attach it. Then, using a drill press, drill into the barrel through the existing hole, about halfway through. Take a piece off the end of that drill bit (tool steel is hard), and use it for a pin, then put a spot weld over it, and grind flush.

 

[Cannibul]

Except the BATF doesn't use a tape measure.

How about a serious reply?

Really?

How do they measure the rod?

 

[Carl N. Brown]

Commercial grade yardstick?

Tabs and rivets on tape measures can be off enough to be serious for NFA purposes.

 

[Reloadron]

Commercial grade yardstick?

Tabs and rivets on tape measures can be off enough to be serious for NFA purposes.

They use a Starret 36" Steel Flat Rule Starret Mfr Part #: 52677. This rule is subject to periodic calibration compared to a much more (at least ten times) accurate standard of measurement using a shadow graph method on an optical comparator. The highly technical term for this would be dead on balls accurate (My Cousine Vinny). There you have it and you know I would never lie about something this serious.

 

[MachIVshooter]

Flash hiders must be soldered with silver solder, welded completely around, or blind pinned and then welded over the pin, to be considered "permanent".

Those are the three prescribed methods, but nowhere in the determination does it say that they are the only acceptable methods. Any method that substantially damages the muzzle before it breaks free is permanent. There are methods that would be far stronger and more difficult to undo than silver solder or P&W.

Having said that, pin & weld is simple, and that they specifically note that as an acceptable method would leave you with some defense even if if failed the "test". It's also the easiest to undo without damage if you ever decided to change the muzzle device. You risk annealing or temper embrittlement with silver soldering, and full circumference welds are really permanent, as in lobbing off the barrel behind the weld, recrowning and rethreading to change anything.

If it ever comes into question, their method for determining if you did it correctly is: Place upper in a vise, put a pipe wrench on the flash hider, and go to town. If the flash hider comes off, you go to jail. If your barrel twists first, they give you back your ruined barrel. At least that is my understanding, but I can't find the link to back it up...

There isn't one. The barrel twisting first is not part of the criteria, though. The only spec I have heard (many times) is that it holds at 200 ft lbs. The other common language is that it substantially damages the muzzle during removal. We don't seem to have any definitive answer on if the muzzle device itself fails in front of the attachment point, although I'm inclined to think that if the muzzle device crushes or rips apart before coming loose, it would be considered permanent.

 

[BSA1]

My intent is to totally build a AR myself from parts. Since I am lacking the necessary tools and skills the permanently attached flash suppressor means I will have to farm this part out. I don't know of any local "gunsmiths" that I trust to do this work. (Actually I don't think there are any local "gunsmiths" period but I digress).

Of course the easiest route is probably buying the barrel with the flash suppressor already attached made by a reputable company. With the information I have received here I will know what questions to ask.

Thanks again for all of the information.

 

[Tirod]

For the most part the industry has already figured this out, to the satisfaction of most builders. Barrel lengths as stated in the ad are generally (yes that's imprecise) accurate, so a 14.5" barrel is just that. What would then be needed and what is marketed is a flash hider that is long enough when pinned to meet the 16.1" wiggle figure for NFA purposes.

In the big picture it then results in a firearm that is highly resistant to future change where someone would be able to change a front sight base or gas block, add or remove a free float, etc. It also slightly reduces the overall ballistic performance. As discussed on a lot of AR forums that means future changes involve either more gunsmith level work, and expense, or buying another barrel. It becomes a $150 road block all for aesthetic purposes, as most who have handled pinned and welded 14.5" and full on 16" barrels with flash hiders find little difference in them.

The option remains, however, and that is up to the builder.

 

[BSA1]

If it ever comes into question, their method for determining if you did it correctly is: Place upper in a vise, put a pipe wrench on the flash hider, and go to town. If the flash hider comes off, you go to jail. If your barrel twists first, they give you back your ruined barrel. At least that is my understanding, but I can't find the link to back it up...

This brings to mind the Witch trials in colonial America.

The test was to dunk the person on trial completely in water. If she floated to the surface then that was proof she was a witch.

If she drowned then that was proof she was not a witch and not guilty of practicing witchcraft.

I can easily imagine the BATF agent handing back my ruined, twisted barrel and saying "Congratulations your flash suppressor passed the test."

All will not be lost as I will have a barrel that is great for shooting around corners.

 

[Reloadron]

My intent is to totally build a AR myself from parts. Since I am lacking the necessary tools and skills the permanently attached flash suppressor means I will have to farm this part out. I don't know of any local "gunsmiths" that I trust to do this work. (Actually I don't think there are any local "gunsmiths" period but I digress).

Of course the easiest route is probably buying the barrel with the flash suppressor already attached made by a reputable company. With the information I have received here I will know what questions to ask.

Thanks again for all of the information.

Are you in an area that requires a permanently attached flash suppressor? Have you given any thought to just using a non threaded barrel and not using a flash suppressor at all?

Below are several of my AR rifles. The fourth rifle in from the left has no flash suppressor and is one of my better shooting rifles sans the flash suppressor. The AR 10 on the right also has no flash suppressor.



Ron

 

[entropy]

When determining the length of shotgun barrels taken in by the shop I worked at, I would close the action (empty) drop a cleaning rod down the barrel until it stopped at the bolt face, mark the rod at the end of the barrel, and measure that against a yardstick taped to the side of the bench. I would do this with three different rods. Rarely did they come out different.

They use a Starret 36" Steel Flat Rule Starret Mfr Part #: 52677.

Yup, that's the one.

 

[BSA1]

Are you in an area that requires a permanently attached flash suppressor? Have you given any thought to just using a non threaded barrel and not using a flash suppressor at all?

Not for the short barrel build. I want it to look like a M-4.

However for another planned build to use for deer and varmint hunting I have thought about going with a 20" barrel without the flash suppressor.

 

[MachIVshooter]

Below are several of my AR rifles. The fourth rifle in from the left has no flash suppressor and is one of my better shooting rifles sans the flash suppressor. The AR 10 on the right also has no flash suppressor.

I'm going with that has a lot more to do with the free floated bull barrel than the lack of muzzle device