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Posted: 8/24/2026 8:09:31 AM EDT
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I recently got a century arms L1A1 sporter with the imbel receiver. I've noticed the locking shoulder was sticking out a tad. I gently hammered it back in. I tested the "headspace" with the bolt and round. It is nicely locked up with no wiggle. Before I shoot this thing I'd like to possibly replace the locking shoulder. I don't have the testing rods or a micrometer. However, the is a electro pencil "5" and a stamped "0" on the locking shoulder. Is this the size I need to order? |
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Ignore anything on an existing LS. Century “technicians” ground on them to make them work. Also reusing used LS can be problematic. My Century used and ground upon LS was walking out of the gun and it sounds like yours may be doing the same. If it ever actually fell out then your gun would fire with the bolt not locked at all. There are designed fixes for that. Besides the number for the headspace adjustment the body of the LS can be had in larger sizes to fit the slightly worn receiver seat. Each time a LS is pressed in place it wears on the receiver. Eventually a standard LS will not be snug fitting enough. This is depot level maintenance type thinking. Anyways they make OS1 OS2 and Iirc an OS3 size LS body. They stand for Over Size 1 and 2 etc. As far as headspace all I would say is to use only what you measure with headspace gages and pin gages. You slip pin gages in where the LS goes and test fit with your bolt and the headspace gages. Edit, I’d order nothing at this point. If the rounds chamber and the bolt is fully locked you’re likely fine. A rough test is to add two round circles of masking tape to a fresh round. About 0.002” per layer of tape, so 0.004” extra. If that fits and the bolt closes you should be good to go. Then of course watch your locking shoulder and make sure it’s not walking out. If it does it’s time to have that replaced. Maybe with a standard body or maybe OS1 size body. Remember the OS is the body of the LS fit to the reciever hole and not the headspace adjustment. |
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I use to live in west Philly. I'm over in Central PA now. I love it here better than Philly. I'm new to the fal platform. I'll probably just take it to a gun smith if the LS starts walking out. I haven't shot it yet so I think it's safe to shoot. But obviously not if it starts walking out. However it does look like century filed the LS to make it work good enough to sell. |
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Unfortunately 90% of local smiths won’t know the FAL system one bit. Pick your smith carefully. I’m no expert either but between here and Falfiles I get the answers that i need. Reusing locking shoulders especially in a receiver that already had a locking shoulder installed you can get what you and I encounter with it walking out. They’re pressed in with an interference fit. That swaged the part and receiver to a degree. The depots would have a precise gage to measure that LS hole in the receiver. Just a rod with different precision ground sizes down its length in steps. If the gage settled on a bigger step then they went to the corresponding oversized LS. |
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Not unusual for the shoulder to protrude a few thousandths when fully seated. Don't go looking for a problem if you haven't verified that one actually exists. If it's walking out, then yes, time for a replacement, full stop. If there's no one around you who can help, there's a site that rents reamers and headspace gauges. Can't recall the name off the top of my head. Pin gauges (or my preferred Starrett Hole Gauge) aren't terribly expensive. Head over to FAL Files for a headspacing how-to. FALs are really easy to work on. I've built a dozen. If you were closer, I'd look at it for ya. |
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