d. Setting the Headspace

Headspace is the distance from the breech face to some datum point on or in the chamber or barrel. For a complete discussion of what headspace is, and how to measure it, see the article entitled "A Headspace Primer," in the October, 1999 issue of CRUFFLER.COM. With reference to the FAL, the headspace dimension is that distance from the bolt face to the portion of the chamber where the internal diameter is exactly 0.400". As with many mechanical assemblies, this distance is expressed as a tolerance, rather than an absolute. According to FN, the headspace tolerance for an FAL is:

FN Factory Headspace Dimensions Minimum 1.6315" Maximum 1.640 Unfortunately, it gets a little more complex. In addition to the absolute maximum, FN also specified a maximum for a new or overhauled rifle of 1.638". That is to say, there are two maximum headspace dimensions, one for a factory new or overhauled rifle and one for a rifle that has been in service. This is shown more clearly below:

FN Factory Headspace Dimensions, New and In-Service Rifles Minimum 1.6315" Maximum, New Rifle 1.638" Maximum, In-Service Rifle 1.640" The equation becomes more difficult when one takes the SAAMI headspace specifications for the .308 Winchester into account. While the 7.62mm NATO and the .308 Winchester are not the same cartridges, and should by no means be considered interchangeable, they are often used synonymously in the United States, and because of their dimensional similarities, only gauges and reamers for the .308 Winchester exist. The SAAMI specification for .308 Winchester headspace dimensions are noted below:

SAAMI Headspace Dimensions, .308 Winchester Minimum (GO) 1.630" Maximum (FIELD) 1.640 You'll note that there is no "NO-GO" specification. SAAMI doesn't specify one. The NO-GO specifcation, measurement, and gauge are products of the gauge makers, and can be whatever the manufacturer decides it should be (within the bounds of the minimum and maximum dimensions). This is why the Forster .308 Winchester No-Go Gauge measures out at 1.634", while the Clymer .308 Winchester No-Go Gauge measures out at 1.636". However Forster's Field gauge measures out at 1.638", inidicating that Forster builds a .002" margin into its gauges that is not the same as the SAAMI specified .308 Winchester maximum headspace dimension. For this reason, we opted to go with the Clymer gauges. Taking all this into account, the consolidated headspace dimensions look like this:



Consolidated FN Factory and SAAMI Headspace Dimensions, New and In-Service Rifles Minimum, SAAMI 1.630" Minimum, FN 1.6315" Maximum, FN New Rifle 1.638" Maximum, FN In-Service Rifle and SAAMI 1.640" Optimal assembled FAL headspace range then, is: 1.6315" < Rifle Headspace < 1.638". As you can see, it is possible to build a rifle with a chamber within SAAMI specification for .308 Winchester, but undersized for the FAL. Since we weren't building a match rifle, but rather a military style self-loader, we opted for fairly generous headspace dimensions so as to ensure compatibility with as wide a range of surplus 7.62mm NATO ammunition as practicable. Consequently, we decided to use the Clymer 1.636" NO-GO gauge as our headspace benchmark. Setting headspace with the use of Elliott Enterprises Locking Shoulder Sizing Rods is surprisingly simple. The rods themselves are basically a pair of stepped cylinders that are precision machined for diameters each ranging from .2454" to .2766". One first diassembles the bolt using the extractor tool, and then thoroughly cleans and degreases both the bolt and the chamber. Dirt or foreign matter can cause erroneous or misleading headspace readings. We used the vise to hold the receiver, muzzle tilted downward, shimmed between two blocks of wood. The stripped bolt was assembled into the bolt carrier, the Clymer NO-GO Gauge inserted into the chamber, and the smallest diameter section (.2454") of the smaller of the two rods inserted into the locking shoulder hole in the receiver. The rod was held against the rear edge of the locking shoulder recess and the bolt - carrier assembly permitted to ride home. If the bolt closed, the process was repeated with the next larger section of the rod. The iterations continue until the bolt will not close under "two thumb pressure" (that scientific term comes from the Canadian armorers manual for the C1A1). You now know the smallest size of locking shoulder that you'll need. At that point, the NO-GO gauge is removed and the GO gauge inserted into the chamber. Using the same section of rod in the locking shoulder recess, the bolt was again allowed to ride home. It should (and did) close readily. Keep placing larger diameter sections of the gauge in place and trying to cloe the bolt. When you find where the bolt will not close, back off one size and retest. This is the largest size shoulder you can use relative to the smaller size that would not close on the NO-GO gauge. From this you can determine a range of locking shoulder sizes that wil yield positive results. If the locking shoulder that came with your kit is within thiw range, you're in business. From this, we were able to determine that the .257" locking shoulder supplied with the kit was eminently serviceable.



Seated Locking Shoulder Once we selected the proper locking shoulder, the receiver was laid on its left side on a section of railroad tie. The oblong end of locking shoulder was carefully lined up with the corresponding receiver recess and started with a few taps of a hammer. Once started, the locking shoulder was driven home using a 3/8" pin punch and healthy hammer blows. Interestingly, the amount of effort needed to drive the was not extreme; bringing the hammer four or five inches

Uninstalled

Locking Shoulder Image Credit:

Arizona Response Systems

ARS publishes an excellent FAL Workbook by owner

T. Mark Graham above the punch was sufficient to generate enough force to seat the locking shoulder. Once the locking shoulder was fully seated, we repeated the headspace gauging, ensuring that the bolt would close on the GO gauge and not on the NO-GO or Field Gauges.