AR15 Specifications – Viking Armory

AR-15 Bolt Carrier Group (BCG) Test Pin Tray

I started working on a holder for the AR15 Bolt Carrier Group (BCG) Pins. The idea came from School of the American Rifle. I wanted to be able to remove the pins if needed. I also did not want to paint my pins for GO / Warn / NO-GO. Here is what I came up with.

Got everything printed up in the right colors and numbers. You can switch it up how ever you like:

AR-15 BCG Test Pin Tray What you print — Everything printed up in the right colors

Then I put it all together. I had to cleanup everything with sandpaper, file and an Exacto knife. With a little help from a small nylon hammer. I got everything in place. Even tried a little infill using model paint.

Added all the pins in:

So far it is working out pretty good. It is another tool in the toolbox when troubleshooting AR15 Bolt Carrier Groups (BCG) The pin sizes are born out of the data I pulled from my research HERE.

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All Documents posted on this site are for informational use only. If you make ANY modifications to your Weapons based on this site, you do at your own risk! If done incorrectly, you can render you weapon unsafe and / or unusable.

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AR-15 Lower Receiver Diagrams – Working Document

Working Document for the Lower measurements. References Below

Receiver Extension Drawing with pin gauging

AR15 Receiver Extension Technical Diagram

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AR-15 Upper Receiver Diagrams – Working Document

I am using this as a working documents to be used as I inspect a rifle.

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Torque Values

My Torque Values:

AR Compensator (Flash hider) No Torque, timing value with the procedure in the Army TM. Hand tight and then tighten a minimum of 90 degrees but no more than 450 degrees to timing. Don’t over tighten, don’t loosen.

AR Barrel Nut 30 Ft. lbs. Minimum, not to exceed 80 Ft. Lbs. to align the next slot in the barrel nut. The 80 Ft. Lbs is not stated in the TM, but I don’t know how you would line up the gas tube, without going over 30 Ft. Lbs. Unless you use shims. I don’t think most folks will have any laying around. This torque spec is common across the community and internet.

AR Carrier Key Screws 50-58 INCH pounds torque

AR Lower Receiver Extension (Buffer Tube/Castle Nut) 40 Ft. lbs for both Rifle and Carbine.

M-LOK Accessories:

For attaching metal accessories to metal hand guards: 35 in/lbs

For attaching polymer or metal accessories to polymer hand guards: 15 in/lbs

For attaching polymer accessories to metal hand guards: 15 in/lbs

The installation torque values are not minimums, they are recommended limits. The nylon patch compound may slightly affect the torque reading if using an in/lb torque wrench.

Using a small hex wrench should prevent over-tightening. Remember that the recoil lugs are doing most of the work, and excessive torque on the nuts is not required

My Comments:

The rest of the items in the research below I could not find in the Army TM, manufacture website or in common reference. Until I can find it, I am going with ‘tight’ and the appropriate thread lockers. ‘Tight’ might be the values listed.

I am not saying that the info below is wrong or bad. I could not readily verify it. The above is what I will use, at the end of the day I am responsible for my decisions and you are responsible for yours.

########### RESEARCH ITEMS BELOW ###########

AR Compensator (Flash hider), 15-20 Ft. Lbs. Torque *1

AR Compensator (Flash hider) *3 (No Torque, timing value)

AR Handguard Screws, 20-30 inch pounds torque *1

AR Gas Block Set Screws, 25-30 inch pounds torque *1

AR Barrel Nut, 30 Ft. lbs. Minimum, not to exceed 80 Ft. Lbs. to align the next slot in the barrel nut. *1 *5

AR Barrel Nut, 30 Ft. lbs. *3 (I cant find the 80 Ft. Lbs. In the TM)

AR Carrier Key Screws, 50-58 INCH pounds torque *1 *2 *3

AR Grip Screw, 15-20 inch pounds torque *1

AR Lower Receiver Extension (Buffer Tube/Castle Nut)

Rifle: 35-39 Ft. Lbs. *1 *3

Carbine: 38-42 foot pounds *1 *3

M-LOK Accessories: *4

For attaching metal accessories to metal hand guards: 35 in/lbs

For attaching polymer or metal accessories to polymer hand guards: 15 in/lbs

For attaching polymer accessories to metal hand guards: 15 in/lbs

The installation torque values are not minimums, they are recommended limits. The nylon patch compound may slightly affect the torque reading if using an in/lb torque wrench.

Using a small hex wrench should prevent over-tightening. Remember that the recoil lugs are doing most of the work, and excessive torque on the nuts is not required

KeyMod Accessories: *1

Polymer to metal: 15 in-lbs

Polymer to polymer: 15 in-lbs

Metal to metal: 30 in-lbs

Picatinny Accessories: *1

Polymer to metal: 15 in-lbs

Polymer to polymer: 15 in-lbs

Metal to metal: 35-60 in-lbs

Ref:

*1 https://www.youtube.com/watch?v=Ah6WISs6IfY

*2 https://www.youtube.com/c/InstructorChad

*3 ARMY TM 9-1005-319-23&P Nov 2008

*4 https://www.dropbox.com/s/jrf9nwxnizjy6ql/M-LOK_Tips.pdf?dl=0 (Magpul MLOC instructions)

*5 https://www.youtube.com/watch?v=tcMqwofYTn0 (Brownells)

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iGauging Firing Pin Protrusion Gage Holder

After I made the plugs for the iGauge to check firing pin protrusion I realized 2 things.

1. I needed to sand down the plug just a bit so it would fit into the hole to get a negative reading.

2. I still had a hard time holding the bolt in a consistent manner. So I came up with the iGauge Firing Pin Protrusion Tool:

Naked:

iGauging Firing Pin protrusion Gage holder In the begining — iGauging Firing Pin protrusion Gage holder, 1st try

Dressed:

Then I added spots for boat tail NO-GO and Field Gage:

Naked:

iGauging Firing Pin protrusion Gage holder with no-go holders — iGauging Firing Pin protrusion Gage holder with AR-15 boat tail No-Go and Field gauge holders

Dressed:

iGauging Firing Pin protrusion Gage holder with Friends — iGauging Firing Pin protrusion Gage holder with AR15 bolt, boat tail no-go and field gauges

Stuck 4 non-slip soft rubber feet on it:

iGauging Firing Pin protrusion Gage holder Back

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iGauging Plug for Firing Pin Protrusion Measurements

I was watching this video from School of the American Rifle: 5 Colt BCG Physicals (Video link starts at 16:06) and noticed that he had to modify one of the included extension shafts of the iGaging Digital Depth Indicator Set so the firing pin would not go into the threaded hole. That got me thinking about printing something up. This is what I came up with.

iGauging Firing Pin Plug01 — iGauging Firing Pin Plug 01

The threaded plugs on the bottom don’t have the ejector notch the the top two have. I like the notched one better. I don’t have to remove the ejector to use. Both are sized to fit snug in the bolt face without getting stuck by the extractor. The plugs also help hold the bolt in place while testing.

The bottom is very smooth and will be able to help you get accurate and constant readings. AR-15 firing pin protrusion should be 0.028 to 0.036 Check out the reference page for more info.

It is difficult for me to hold everything in place to get an accurate reading. I think I will start working on a holder. More to follow.

You can download the 3D printer files HERE.