Greeting, I was wondering if I could get some help with a problem. First this is a parts kit rifle, STG 58 kit, on a Type II DSA receiver. I never had any problems until recently, the looking shoulder is backing out of the receiver when the rifle is fired. I was wondering what I need to do to correct this. Thanks.

I have built several FAL's when the parts kits were cheap.

Having said that.  I remember the Locking shoulder being very tight to get into place.  Like needed a small maul hammer to get it to seat.

The geometry is such that the force is transferred directly to the rear and that shouldn't cause the locking shoulder to walk out.  Unless it is undersized.

The other thing could be that the shoulder isn't square with the rear of the bolt.  You can check by looking at the wear marks on both parts. If they aren't fit properly the impact from the bolt on firing could be forcing the shoulder out.

I built a bunch back when they were cheap too, but IIRC, someone was making oversized pins once upon a time because of this. Hopefully someone comes along with the info.

A used locking shoulder that came in the kit when it was built?  The ghetto temp fix is to stake it but that is not a satisfactory fix.  

The proper fix is to use an OS locking shoulder.  They have always been a part of the fal tool room as designed for later military rebuilds.  They have an oversize, oversize 1, and oversize 2 IIRC.  

ETA- oversize refers to the shank and head fit to the receiver and not any headspace adjustment.

clipped from a Rawles post:

Regarding the "Shoulder, Locking" there are 60 different sizes in
four ranges :    1 - 15
                       1.1 - 15.1
                       1.2 - 15.2
                       1.3 - 15.3

The above sizes are also shown in some publications in this format:

Shoulder, Locking sizes                     1 - 15
                                 1/1 - 15/1
                                 1/2 - 15/2
                                 1/3 - 15/3


I would post over on FAL files and ask the question.  Might be a dimensional issue with the DSA receiver.  The borg like fal knowledge could confirm or dispel that possibility.  You will likely also find sources for your replacement OS ls.  Gunplumber is one source and a FAL builder expert over there.  There are others but my brain isn't spitting out the commercial guys' user names.

Send it to Randy Kline aka Sledgehammer out of TX. I sent him one of my l1a1's that had an issue, total turn around was 8 days and cost was extremely reasonable.

I should first say, you should call dsa and find out if your fal is one of their early builds and they may fix under warranty.

I recommend as well that you send it to Randy Kline in Texas. His bag O' FAL tricks is extensive. You won't be disappointed in his work, prices, and turnaround time.

Randy has worked on my FAL.

First class work. Reasonable prices. Quick turnaround.

Easy button.

Check here for oversize locking shoulder The dealer wharhouse . They are listed as L1A1 but the locking shoulder is interchangeable between metric and inch models. mic you current shoulder and get the larger size needed.
http://www.the-dealer-warehouse.com/FAL-L1A1-Rifle-Parts/L1A1-Locking-Shoulder-Unissued.html

This is a home build using a DSA receiver. The age of the rifle is at least 15 years old and this problem has started in the last few years. I have not shot this rifle much, usually just 20 to 40 rounds.

Thanks everyone for the replies