Receiver 

• Styles
• Types
  • Machined Receivers
  • Stamped Receivers
    • Material
    • Ready-to-assemble Receivers
    • Stamped Flats
    • Pre-bent Blanks
• Metal Bending Methods
  • Press Bending Brakes
  • Hand Bending Brakes
• Rivet holes
• Dimples
  • Magazine Well Dimples
  • Feed Ramp Dimple
  • Trigger Swell Dimple
  • Safety Selector Dimples
  • Axis Hole X and Y Dimples
• Center Support Pin

The receiver is the starting point for any build.  If you have an adequately supplied shop, you can make an AK receiver from scratch (and completely legal, I might add) for literally a few dollars. 

Styles

The style of AK you are planning to build will somewhat dictate what kind of receiver to look for - the most important factor being if you are going to build an RPK-style since this style is unique in these differences:

1. Thicker receiver material (1.5/1.6mm vs. standard 1.0mm) 
2. Reinforced trunions which require special bulges in the receiver
3. Machined receivers more common

In this pic of the Romanian RPK, note the RPK-specific receiver with the thicker trunion swells:

  This comparison pic is from the Robarm website:

All else is "normal" about RPK assembly in comparison to a standard AK.

Types

An AK receiver can be either machined from a solid block of steel, or a sheet metal "stamped" receiver.  

Machined Receivers

Fabricated from a block of tool-grade steel such as 41xx steel.  There isn't any good BIY blueprint I have found for a machined receiver, and construction of this type of receiver consists of use of a mill/drill to remove the material from the solid steel block.  Expect to spend $250 - $450 for a milled receiver.  These are considered "100%" firearms and will require an FFL for purchase.

There are only a few sources for BIY machined receivers:

• The Firing Line customers always rave about their "best quality" milled receivers.  They have conventional receivers AND underfolder style receivers.
• OhioRapidFire is rumored to be working on a milled receiver offering.   
• Inrange may have receivers available (not listed on their site).
• Arsenal sells complete milled rifles.

Stamped Receivers

aka Sheet Metal Receivers.  We don't have the sheet metal stamping presses to turn these out in a  cookie-cutter fashion, but "home made bent sheet metal dremel-cut receivers" sounds odd!

Material

These consist of tool-grade sheet steel such as 41xx.  This is also referred to as hot-rolled or cold-rolled steel, depending on the alloy.  This is NOT galvanized steel!  4130 steel is usually considered "the best" but other "tool-grade" steels can be used, so long as it is suitable quality for applications such as in the aviation industry.

Coldsteel uses ASTM A.064 (16 gauge) Cold Finish Sheet Steel (same as A1011) for his RPK receivers.  He will also bend metal that you supply for him!

Other higher-strength steels to look for:

It should be mentioned that this is NOT the mild sheet metal you would find at Home Depot because that mild steel simply is not strong enough for a receiver.

The best and cheapest sources for tool-grade sheet steel are aircraft suppliers (!!!):

Aircraft Spruce

Airparts

Alcobra

Wicks

The thickness to look for is 1mm-1.5mm thick (0.40"-0.65").  Normally you get sheet steel in "gauges" and not thickness:

Note that if you measure the FINISHED thickness it may measure slightly under the SPECIFIED thickness, but this is expected... numbers are rounded just like a measurements for finished lumber.  Don't let this confuse you!

Ready-to-assemble Receivers

Several firearms manufacturers have created these for the BIY community.  Although these are simply sheet metal boxes with holes drilled in the them, they are considered "100%" firearms and require an FFL for purchase.

Here's a list of current vendors (no preferences listed)

• Vulcan Arms (formerly known as Hesse)
  • Pros
    • Low Cost.
    • Available from many independant dealers like DSSPRO.
    • Receiver holes are already hardened.
    • Available with longer 5.45/5.56 ejector that can be trimmed for 7.62 caliber.
    • A version is available for the many underfolder kits currently available.
    • Receiver is delivered with a phosphate finish.
  • Cons
    • Front Trunion holes are misaligned.
    • Quality of workmanship usually not highly regarded by customers.
    • Ejector is NOT hardened and will fail w/o additional heat treatment.

• Ohio Ordnance Works
  • Pros
    • Reportedly top-quality workmanship.
    • Available with either 7.62 or 5.45/5.56 caliber ejectors.
    • Completely heat treated receiver - not just the pivot pin holes.
    • Ships without pre-drilled rivet holes so pre-alignment is not an issue.
  • Cons
    • More expensive.
    • The safety selector hole is not properly aligned and will leave a gap between the cover and the selector when in SAFE.  In some cases the hole is too high and the selector must be filed down to fit with the top cover.
    • Only available in standard rifle configuration, no underfolder model is available.
    • "in the white" unfinished metal - no finish or phosphating (this may be a Pro?).
    • The heat treatment makes drilling the rivet holes difficult.

• Global Trades
  • Pros
    • Good company reputation.
    • Available in many different styles.
  • Cons
    • More expensive.
    • These use thicker 1.6mm material so custom-fitting of trunions, etc. is required.
    • ALL styles, even those that are technically "80%" models, require an FFL.  It is not clear why they chose to make these require an FFL.
    • Some styles require additional machining work to complete.
    • Since this is a relatively new offering, not much is known about the quality.

Stamped Flats

There are also pre-drilled sheet steel flats that have all of the dimples pressed in, holes drilled, etc. and these require only bending into the right shape to work.  These are considered "80%" receivers and require no FFL for purchase.  Here's an example:

Sources: 

Tapco

FAC

K-Var

Pre-bent Blanks

You can also order a pre-bent sheet steel shell that has no holes or dimples, it is just a piece of bent sheet metal, with the proper dimensions for an AK receiver.  These are considered "80%" receivers from a legal perspective and require no FFL for purchase:

Standard Style:   RPK Style: 

Here are the some of most common places to find these blanks:

Standard model blanks

http://bentmetal.homestead.com/bentmetal.html

http://www.acearms.com

Update - coldsteel now has standard blanks:  http://www.coldsteelsolutionsincorporated.com 

RPK model blanks

Email coldsteel4us for RPK-style blanks or go to his website here:

http://www.coldsteelsolutionsincorporated.com 

Metal Bending Methods

Sheet steel receivers, either home made or pre-stamped, are bent into the proper dimensions by some sort of sheet metal bending brake or by a press-based bending frame.  

When you are done, you will have a receiver shell, legally NOT considered a receiver - some call this a "0%" or "80%" receiver... that has the proper measurements and needs the components to be added.

Press Bending Brakes

These are basically a steel box sized large enough to put an unfinished receiver into - 1.25" thick, plus the thickness of the metal you will use.  The sheet steel is fastened to a steel plate, lubricated, and smashed down into the box to bend the sides into shape.  The top is bent over usually by careful use of a hammer.

Example of a press-based brake:

http://geocities.com/partskitbuild/akm.html > follow the "Bend" link for more...

More examples:

 - this one from Thud:

 - this one from SaavySurvivior:

Hand Bending Brakes

The sheet metal brakes at Harbor Freight may be used.  The smaller brakes require attachment of reinforcement plates to *cleanly* make the bends, otherwise the bends will be shoddy.  The larger the brake the better!  Looking at my AceArms blanks, you can see slight clamp marks where it appears the brake was clamped, so I think this is what they use.  This method is a little more tricky, because you need to get everything in alignment side-to-side, and you still have the problem of bending the top of the receiver inward.  

Rivet Holes

The location of the rivet holes is NOT a simple "drill here" exercise.  The nature of assembly of the receiver to the frame block (aka trunion) requires drilling at the time of assembly, so as to accommodate any slight variations introduced from the sheet metal bending process from part to part.  Thus the "pre-drilled" receivers should work but may require some tweaking to get the holes to line up properly with the trunions.

The "index" for all of the other holes is the front trunion which should be drilled first - all of the other holes depend on the location of the front trunion.   

There are several templates floating around and for the most part are a good fit.  I have collected these on my website here as I find them.  The trunion holes should be hand-fit to your receiver to ensure a proper fit.

Use transfer punches to locate the trunion holes.  Trunion holes are sized at 4.5mm and the center holes (2nd from the front) are 4mm holes.  Most of us don't have metric transfer punches, so use 5/32" transfer punch for the 4mm hole, and 11/64" transfer punch for the 4.5mm hole.

Drill SLOWLY and check your measurements often.  Recommend use of a drill press and step-cut - starting with small bits and working up to larger bits - to keep the holes as centered as possible.  If the holes get off-center, you may be able to "walk" the bit back to center.  If it gets too bad, you may have to TIG weld the holes up and re-drill.

Dimples

Moved to the dimple page (link to the left)

Center Support Pin

Moved to the center support pin page (link to the left)