Fulton Armory M14 receiver

Fulton Armory semi-automatic M14 receiver

I’ve been a big fan of the M14 rifle for years. I’ve decided to tackle a MK14 MOD 0 and/or EBR build as part of an upcoming post. After I secured my Sage enhanced stock chassis from Brownells, I needed an action. The first company I reached out to was Fulton Armory.

A long time player in the M14 game, Fulton Armory offers shooters the ability to buy a stripped M14 semi-automatic receiver for a reasonable price.

I’ve been working on bolt rifles with an occasional AR for so long that I forgot how intricate the receivers on rifles like this are.

You’ll find M14 receivers made a variety of different ways. I went ahead and cut and pasted the following from Fulton’s website:

FA M14 Receiver Specifications

Precision CNC Machined From “Lost Wax” Investment Casting

8620 Alloy Steel

Material & Geometry Per Mil Spec With Enhancements For Semi Auto Use

Proper Core & Case Heat Treat per Mil Spec

100% Made in U.S.A

Marked “U.S. Rifle 7.62MM M14”

*BARRELS, BOLTS, & RECEIVERS MUST BE PROPERLY HEAD SPACED PRIOR TO USE. FAILURE TO DO SO MAY RESULT IN FIREARM DAMAGE, PERSONAL INJURY, OR DEATH*

The M14/M1A (& M1 Garand) receiver has the most complex geometries ever designed in an issue US martial arm, making it the most difficult receiver ever manufactured. While M14/M1A receivers may all look pretty much the same, they are NOT. After 25 years of inspecting M14/M1A type receivers we have found, and continue to find, many that are fatally flawed (not fixable), including current as well as defunct companies, and, AT ALL PRICE POINTS.

So, what makes a good receiver?

1. Proper material. Critical to safe and durable operation.

2. Proper heat treat of case & core. Critical to safety and durability.

3. Proper right & left locking lug helix: Ensures full “mirror image” contact to bolt lug helixes to prevent collapse of headspace. Critical to safe operation & durability.

4. Proper firing pin bridge location: Prevents out-of-battery detonation & jamming of the bolt. Critical to safe operation.

5. Proper op rod shelf height & width: Ensures op rod is fully supported to prevent op rod “roll out” which causes premature cam deformation. Critical for durability.

6. Proper firing pin seat: Prevents damage to firing pin tail when bolt bottoms at the inside rear of receiver tail. Critical for safety.

7. Proper height, depth & interval of rear sight receiver serrations. Critical for durability of rear sight function.

8. Proper op rod Spring guide slot depth & location. Prevents spring guide binding & poor magazine capture.

9. Proper bolt stop window height & width, and, proper location of pin holes in bolt stop bosses. Critical to bolt stop function and durability.

10. Proper sharpness, depth & well defined scope side mounting threads. Critical to proper scope mount capture & durability.

11. Proper receiver raceways for bolt. Allows proper bolt/receiver locking lug contact without binding. Critical to safe operation.

12. Proper forward bolt location: Ensures proper case support

Cast vs forged vs billet: What’s the difference?

– Machining from billet/bar stock requires no expensive up front capital costs for molds or dies and is normally selected for very small runs. Low up front costs, but very high per part machining costs. Highest receiver cost to end user.

– Machining from a forging requires expensive die sets, which, as the military did, can forge the steel to a semi finished shape which reduces machining time. Normally selected for very high quantities.High up front costs, but moderate per part machining costs. Moderately expensive receiver cost.

– Machining from a precision casting process requires very expensive molds that can cast steel to a nearly finished shape and is normally selected for moderate quantities. Very high up front costs, but lower per part machining costs. Least expensive receiver cost.

A poorly machined billet receiver gives you a very expensive bad receiver.

A poorly machined forged receiver gives you a moderately expensive bad receiver.

A poorly machined cast receiver gives you the least expensive bad receiver.

It’s all about the material, geometry & heat teat, not the process selected.

As to strength: Why did Fulton Armory select machining from a casting as our method?

About 10 years ago a customer sent in a Federal Ordnance M14 that had “blown up” for us to perform a tech inspection. Shooter was okay. Federal Ordnance, now defunct, produced thousands of a very poor quality receivers (poor geometry, but good material & good heat treat), that was machined from a casting and had digested one of those infamous CBC 75 .308 cartridges that produces “in excess of 140,000 copper units” of chamber pressure (nominal is 50,000). This CBC 75 ammo blew up, and continues to blow up, any and every rifle that see’s that 140,000 CUP. Here’s the interesting part: The receiver held. There was a partial crack in the receiver below the right locking lug of the receiver, but it did not detach or fail. The locking lugs of the receiver were untouched, the locking lugs of the TRW bolt had been impressed into the receiver’s lugs by something like 10,000ths of an inch; huge depressions in both the right & left bolt lugs. The bolt held. The barrel was in perfect shape. So, what “blew up”? The case failed, released the gasses into the mag well, peeled the bottom of the bolt away, inflated the magazine and blew the stock apart. A poorly machined cast receiver, even with poor geometry, but with proper heat treat & proper material, is vastly stronger than the rest of the system.

About 20 years ago we inspected an original USGI forged M14 receiver that had blown apart into 4 pieces on the firing line at The National Matches, Camp Perry, OH. Shooter was knocked out, but fine otherwise. So, why did the USGI M14 blow apart in 4 pieces? Bad receiver? No (good geometry, good material, good heat treat). Bad ammo? No (issue LC). Bad assembly techniques? No (well built rifle). Bad bolt? No. What then? The barrel failed due to bad lot of steel. The heavy match barrel had split from the chamber mouth down to the heavy oversize op rod guide. When the barrel split open wide at the receiver ring it introduced lateral forces to the receiver ring, and split it apart like an axe splitting firewood. M14 receiver rings are not designed to take chamber pressures nor lateral forces, no matter how they are made.

These, and many other failures over the decades demonstrated to us, in a very hands on way, the same thing Col. Hatcher found in his destructive testing of the M1 Garand receiver: That J.C. Garand’s receiver design is so remarkably strong that inevitably some other part of the rifle system will fail long before the receiver, providing it has good geometry, good material and good heat treat. Cast, forged or billet.

So, to keep the receiver costs affordable for all of our customers, we chose to cast & machine, while spending a whole lot of time and care in assuring the quality of the machined geometries, correct 8620 alloy steel, and proper heat treat for case & core. The finest M14 receiver available, at any price.