What is a locking shoulder guys?

n/a

See above.

llama

On a FN-FAL or L1A1 they control the headspace and barrel timing (so the sights and gas port are at TDC)

They look like a little post about 1" long with a foot on one end.

n/a

How do they work and what do they do?

dcs shooters

This is it, it controls head space [;)]

p3skyking

A locking shoulder is the physical block that keeps a bolt from recoiling during ignition of a cartridge.
On a bolt action rifle (or semi)is is the part of the receiver that the bolt locks on.
Same with locked breech semiauto pistols. The P.38 (and by extention the Beretta 92 which uses the same system) is a good example of a pistol with a locking shoulder.

amparts

The locking shoulder ONLY controls head space not the indexing of the barrel, on an L1A1 that is controlled by the breeching washer and barrel shoulder on metric barrel. Locking shoulders came in several diameters (4 from Zero series to series 3)to allow worn receivers to be saved, also about 16 sizes, that means the front to back distance to allow the head space to be controlled and adjusted. There is also a locking should that has no cut for the bolt to lock up against this allows you to "custom" cut it to save a barrel receiver unit. This same system was also used on the FN49, AG 42, Hakim and a few others. .

BigLoop22

Sage1,

You can but a whole mess of them, from just one seller:

L1A1 Lithgow Locking Shoulder Armorers Set

http://www.GunBroker.com/Auction/ViewItem.aspx?Item=387917924







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