Tutorial: Restoring the CAI L1A1 Thumbhole Sporter

Congress banned the importation of “Assault Rifles” in 1989. Certain features differentiated a “sporting rifle” from an “assault rifle”. Features included: detachable magazine, pistol grip, bayonet mount, flash hider, and folding stock. Importers modified their rifles to comply with the law by substituting a thumbhole stock for the pistol grip, removing bayonet mounts and flash suppressors, as well as the threads for installing a flash suppressor. ATF accepted these cosmetic changes as turning an assault rifle into a sporting rifle. ATF changed their interpretation in 1994 and disallowed the thumbhole stock as a means of neutering an otherwise normal rifle.Century Arms imported many of the FAL/L1A1 type rifle from 1989 to 1994. They were assembled in Canada at CAI’s sister company, CIA; utilizing Brazilian (IMBEL) and Argentine (DGFM-FMAP) receivers and mostly British parts. Argentine receivers are differntiated from the Brazilian by a relief cut behind the hinge pin hole. Since both the Brazilian and the Argentine receivers were originally patterned for the FAL rifle, some accommodations had to be made to utilize the L1A1 (inch) parts kits.

The terms “inch” and “metric” create much confusion. They should really be called FAL (European) or L1A1 (Commonwealth) as neither has any metric threading. That’s right . . .. there is no metric threading on a “metric” FAL, everything is standard imperial thread. But the names have stuck. There are some differences between the L1A1 and the FAL that require modification to use L1A1 parts on a FAL receiver. CAI did some of these modifications on some receivers, but not with any consistency – so these receivers are hybrids, being neither FAL (metric) or L1A1 (inch). Modified areas on the receiver may include:

magazine well
top cover clearance
folding cocking handle clearance

Section 922 requires a FAL/L1A1 rifle manufactured from imported parts, if it would be banned from import, to have no more than 10 parts off a list of 20. The end result is that you must replace 7 parts with US made ones to comply with federal law. What’s this US Parts thing about?

This tutorial is to help you understand what needs to be done, not to teach you how to do it yourself. ARS can do the work for you, or a modestly skilled person can do the work himself, using this page as a general outline.

You will need some or all of these parts. See schematic

Phillips screwdriver (for removing thumbhole buttpad screws)
square drive (for removing thumbhole pistol grip screws)
flat screwdriver or 7/16 Allen key for grip screw
FAL/L1A1 stock tool (screwdriver incorporating a spring guide)
shoulder stock, plastic or
shoulder stock, wood
buttplate, plastic stock: short, normal, long or extra long, or
buttplate, trap door, wood stock
buttplate screw
buttpad plug, plastic stock
rear sling swivel & screw, plastic stock or
rear sling swivel & screw, wood stock
buttplate wood screw, wood stock only
pistol grip plastic or
pistol grip, wood.
trigger guard with wood or plastic grip plate
trigger guard, wood (machine screw) or plastic (wood screw)
trigger return plunger
trigger return plunger spring
trigger spring plate (if yours has the tab cut off)
trigger spring plate screw
grip screw (1/4×28 socket head is approved substitute)
grip screw lock washer (star type)
fabricated grip stud.

This is what you are probably starting with

This is what you want to end up with.

We need to deal with the naked muzzle.

And we need to get rid of the thumbhole stock. Remove the lower from the upper by unscrewing the hinge pin. While retaining the hammer with your hand, pull the trigger, which will release the hammer spring. You will see underneath a slotted screw or hex bolt. Remove this to free the pistol grip side.If you pull on the edges of the rubber buttpad, you will see two razor slits. Lubricate a Phillips screwdriver and slide into this slit. You will feel a Phillips head screw underneath, about 3/4″ in from the toe and heel. Remove these to remove the buttpad and expose the recoil spring tube plug. Use the stock tool to unscrew this plug and free the spring. The thumbhole stock should now come off.

We also must determine which magazine is suitable. The magazine well is the most significant difference. The FAL uses a small, half-circular cut-out for the front of the magazine well. The L1A1 uses a wide rectangular cut-out. There are corresponding shaped tabs on the front of the magazine. While it is true that a FAL magazine fits in an L1A1, it has no front support for the magazine so does not feed reliably.L1A1 magazines are more scarce and more expensive than FAL magazines, one should simply choose magazines based on what magazine well you have.

It is possible to convert a FAL magazine well to an L1A1 magazine well, but it is challenging.

Here is the clearance for the folding cocking handle. The folding cocking handle requires a clearance cut on the receiver. Once the cut is made, the non-folding cocking handle will still fit, but there is no retention for the cocking handle plunger retaining pin. Should this pin move, the gun cannot be cocked. If your receiver is not cut, you can either use a FAL cocking handle, or cut it and use a folding cocking handle. If it is already cut, you should only use the folding cocking handle.

Here is a tabbed L1A1 top cover with the clearance cuts in the receiver. The L1A1 top cover has two tabs on the rear that fit in recesses cut in the receiver. If your receiver does not have the clearance cuts for the tabbed top cover, you can use a metric top cover, or cut the tabs off the L1A1 top cover.Since L1A1 top covers are far less common, particularly with the tabs intact, it may be foolish to “ruin’ a tabbed top cover by removing the tabs. You can trade it for a FAL.

It is possible to machine the clearances for a tabbed top cover.

The L1A1 magazine catch spring is a larger diameter than the FAL. Its recess must be enlarged. Open this hole to 5/32″. You may need to replace the spring as they get mangled ramming them into a too-small hole.

To fit the thumbhole stock on the rifle, CAI cut off the stud that supports the pistol grip. This stud positions the pistol grip front to rear. Sometimes the stud was cut off, leaving a hole of this size. Sometimes it was punched out, leaving a larger hole. When making a replacement stud, we must take measurements from our receiver.

CAI also ground off the tab at the top of the trigger plunger plate, and often cut the spring and plunger shorter (or used a different spring) – all to function with their thumbhole stock. You can weld up and reshape the tab, or replace the plate. The tab prevents lateral rotation of the pistol grip, as well as supporting the plate. Spring and plunger should be replaced. You may find a combination of square drive and Phillips head dry-wall screws in place of the correct ones. These should be replaced as well.

Fabricating a new stud from round stock. Drilled with a 1/4″ holeSome people have successfully fabricated this stud from a brass pipe fitting, and it is retained by friction. I prefer to match the original and to solder it.

Establishing the shoulder height and the stud depth

Test-fitting the stud in a pistol grip. The shoulder should be flush.

Soldering the stud into the receiver.

Machining a flat on the front of the stud. This limits the travel of the trigger plunger, which is another reason the missing stud results in a loose pistol grip and erratic trigger pull.