Installing flush-mount sling swivel cups

Today I’m going to install three flush-mount sling swivel cups in a Bell &
Carlson stock for my Remington 700. Three because I want to use a Ching sling
with this rifle and flush cups because I’d like a smooth surface when shooting
over any kind of rest.

I have quite a bit of work planned for this stock, but we’ll start simply.
The sling swivels I purchased are Grovtec threaded cups, made right here in Oregon.
They install with a 9/16-18 tap, so I bought a cheap, carbon steel tap as
well.

Additionally, a little Devcon Steel Putty, some mixing sticks and we’re ready
to go.
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Firearms Safety

It’s only right that any discussion of shooting begin with a discussion of safe firearms handling.  This particular article will confine itself to the aspects of safety governing responsible firearms use and set aside, for the moment, safety in design, shopwork, and gunsmithing.

There are only four fundamental safety rules to abide by to ensure safety when handling firearms.  They were first enumerated by the late Colonel Jeff Cooper and have come (in various guises) to be adopted by numerous shooting disciplines and organizations.  I list them here in my own verbiage.

1. Every Firearm is Always Loaded!

From a gunhandling perspective, there is no such thing as an ‘unloaded’ firearm.  Responsibility dictates that at no time should a firearm be treated any differently in one set of circumstances than in another.  In the vast preponderance of cases, when a person negligently shoots themselves or someone or something that they shouldn’t they exclaim “I didn’t know the gun was loaded!”.  That is, perhaps, the case but it was irresponsible to handle the firearm as if it were anything but loaded.

2. Never Allow the Firearm to Point At Anything You Are Not Willing to Destroy!

If a firearm is never pointed in an inappropriate direction, nothing but the ego can be harmed by its discharge.  This is perhaps the most frequently violated rule, and its violators are often unaware of the violation.  As a firearms user, you must maintain a continuous awareness, under all circumstances, of where your firearm is pointed.  It is always pointed at something.  Pick something safe (e.g. the backstop at the range, a target, the floor (assuming you are not upstairs)) and specifically point at that.

3. Keep Your Finger Off The Trigger Until You Are Ready To Fire!

This is the “golden rule” of responsible firearms handling.  A firearm in good mechanical order will not discharge unless and until the trigger is pulled.  (However we have rules 1 & 2 to protect us in the event that our firearm is faulty.)  Make it a point when handling firearms to keep the trigger finger fully outside the trigger guard and fully extended when not prepared to fire a shot.  Ideally, find a bump or stud on the side of the arm to feel with your finger as tactile confirmation that your finger is  indeed where you think it is.

4. Be Aware of Your Target and What is Beyond.

You are responsible for every bullet you fire, from the moment it is fired until the moment it comes to a complete rest.  Therefore you should make sure the thing at which you are shooting is an appropriate target.  This is true on the range as well as in hunting (that’s really the animal you want and not another hunter, or the wrong sex animal, etc.) and self defense (that home intruder is really a bad guy and not your teenager sneaking in late).  Additionally you must be aware of what’s beyond.  A bullet is a stupid thing and may pass through the target, going on to cause further damage or you might miss.  Be sure there is a clear line of sight to a safe and impenetrable backstop.

These rules apply to all types of firearms in all situations.  Think of them every time you are about to handle a firearm and practice to make them habitual.  Demand the same of everyone who handles firearms in your presence.  Shoddy gunhandling is negligent, unacceptable and downright dangerous.  Safety costs little, negligence can cost everything.

 

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Machining an AR-15 upper receiver forging – part III

Step 3, Drilling the lugs.

We’re finally going to create the actual reference point – the pivot pin hole in the front lug.  While this could be done in a vise, using a 1-2-3 block on the bottom of the receiver and indicating the sides (upward facing surfaces) to the same depth, I decided a fixture would be easier.  The lug drilling plate (see Appendix A) aligns the lugs with the bottom of the vise or angle plate and allows for moderately quick fixturing.  I recommend it if you’re going to make multiples.

Receiver clamped in using lug drilling plate. The centerfinder has just been used to find the 'deck' surface.

Receiver clamped in using lug drilling plate. The edge-finder has just been used to find the inside of the front lug.

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Machining an AR-15 upper receiver forging – part II

Setup 2, the deck

Next we’ll machine the deck flat and cut the lugs to size.  In doing so, we’ll establish a reference to the position of the upper along the line established in the first setup.  The real reference will be the pivot pin hole once we have machined enough that we can drill it accurately.

We’ll use the convention that the X dimension goes more positive as the table moves from left to right (as if the cutter were moving right to left) and that the Y dimension increases as the table moves away from you.

Setup the part, using the clamping plate, with the deck up and the thread boss pointed left. Make sure the deck is about 1/8″ above the top of the angle plate, so you don’t cut into it. Indicate the deck to be as horizontal as possible.  It’s still a raw forging at this point, so the surface won’t be perfect – just get it as close as possible.  Less than 0.010″ across the space between the lugs is good.  Dont indicate along the parting line, use the smooth surface to one side or another.

Indicating the deck to horizontal.

Indicating the deck to horizontal.

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Machining AR-15 upper receiver forgings part I – redux

Machining the upper receiver of an AR-15 is an intermediate to advanced machining project.  It is more difficult to make, on manual machines, than the lower receiver, and should only be undertaken by those who already possess a firm grasp of machining fundamentals.  This document is based on the format of the “Ray-Vin” (Ray Brandes) document which describes the machining of a lower receiver forging.

Because of the complexity, a grasp of machining techniques and terminology are assumed.  This tutorial is not intended as a machining lesson for the beginner.

I freely admit that I am not a professional machinist and that there are likely better ways to perform certain operations.  The setups shown reflect my preferences and the tooling on hand in my shop.  There’s more than one way to skin a dog, and you should feel free to modify the instructions to suit your equipment and preferences.

If you have never machined from a forging or casting before, things are a little different than machining from billet. The AR upper receiver forging has no truly flat or truly round surfaces to use as a starting reference, so you must establish references as early in the machining process as possible and then use them throughout.  You have not created complete references until you have points you can measure from to achieve consistent location in the X, Y, and Z planes, as well as theta (rotation).  Don’t worry too much if that doesn’t make sense to you – we’ll fill in the blanks as we go along.

Setup 1, Establishing theta.

In this first setup, we begin the process of establishing our references.  The first reference point we want to create is the centerline of the bore.   This will give us the centerline of the forging.  The best way to create this reference is to use the thread boss at the front of the receiver.  The thread boss is the round ‘nose’ of the forging.

Dial in an angle plate to be parallel to the X-axis on the mill.

Mount the forging vertically using the receiver mounting plate.  Using the quill to run up and down in the Z-axis, adjust the forging to be vertical.  Note that the forging doesn’t have an accurate edge, so you are adjusting for minimum deflection of the indicator, no zero deflection.  Up to 0.010″ is normal, and nothing to be concerned with.  Using a machinist’s square can help speed this up.

Dialing the receiver in to vertical.  The surface isn't perfectly flat, but it's pretty close

Dialing the receiver in to vertical. The surface isn’t perfectly flat, but it’s pretty close

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