SMOS GFY-10 parts issues

[gunsmoke50]

Greetings builders,

I posted here several years back seeking advice on parts for the SMOS GFY-10 lower I bought. Just finally got around to putting it together (life happens), and I mostly have it together, except for a few issues:

1) the front pivot pin I have (Armalite lower parts kit) doesn't even come close to working. What brand do I need?

2)I have a 308 PMAG that fits snugly in the mag well, locks up solidly, but is WAAAY too tall. Receiver halves won't close. Which brand/pattern mags should I be using? Should I just Dremel the PMAG catch indent till it works?

3) Armalite bolt catch is waaay too tall, so much that the bolt carrier won't cycle. Also the GFY-10 lower uses a screw to secure it, not the roll pin I have.

I have a Noveske lower parts kit on the way, but I'm not sure if their current LPK is compatible, since Noveske changed their lower pattern IIRC.

PMAG way too tall

Is this made for an HK style friction pin or something? Or do I need a cross-bolt, like on the old Colt Sporter lowers?

Edited August 12, 2023 by gunsmoke50

[98Z5V]

These guys used to make all of Noveske's uppers and lower, so start there, you're on the right track with the Noveske LPK.  They also (originally) made all the LaRue uppers and lowers, before LaRue brought all that in-house.  Noveske and SMOS parted ways in a pretty harsh way, hence the name of this particular lower that you have. 

This pic:

That's definitely the Armalite AR-10 cut on the back of the receiver, and I'll bet you need to be running Armalite AR-10B mags. 

Which Armalite bolt catch did you try?  10B or 10A?  There's a difference.

[gunsmoke50]

I bought an Armalite match trigger set, it came with the mag release. Fits pretty good in the lower, and functions to hold the PMAG in properly. Just holds the mag too deep in the well.

Any other manufacturers for 10B pattern mags, other than Armalite? I see that Larue makes 20 rounders, but they most likely won't ship to my state.

[gunsmoke50]

After checking, it looks like the mag catch is an AR-10A pattern, since it has the semicircular front on the boss.

My upper is a Noveske, and it has the over-insertion tabs built in. Looks like Armalite pattern mags for me.

The bolt catch is still a puzzle. It looks like a 10B pattern, but the bolt won't cycle at all while the catch is in place. I guess I'll have to try the Larue when it comes in.

[98Z5V]

You definitely needs to stick to Armalite AR-10B patterned parts for this. DPMS mags and Magpul mags are what the AR-10A takes. SR-25 design, not AR-10B design.  

The mag catch won't matter, 10A or 10B.  Won't matter.  I think the 10A is a better design.  Where the catch position is on the mag body is what determines the height when inserted.  The catch doesn't matter. 

It'll sort out.  Just takes some time.  Stick with 10B stuff and it'll all sort out faster, and with less stress on the bank account.  

Pics of what you're dealing with, with the bolt catch, will help.  We have a pretty exhaustive thread about bolt catches, with pics and measurements.

Or, call Stubborn Mule, and ask them what catch to use.  

[gunsmoke50]

 Update:

I ordered a Larue 7.62 lower parts kit, which arrived promptly.

The Larue kit came with a pivot in that was the right length and shape, but was too large in diameter to pass through the hole in the upper receiver! I chucked up the pivot pin in a drill press, and used sandpaper to slim it down. It fits snugly now.

the Larue LPK also came with a bolt catch that functions, but came with a roll pin instead of a threaded pin. All I could find online were DPMS style threaded pins, so I ordered a couple, and hopefully they'll fit when they arrive.

Now, the really annoying part: magazines.

As I stated I'm my original post, the LR-308 style PMAG fit snugly in the mag well, but the AR-10B style over-insertion stops in the Noveske upper receiver prevent the PMAG from locking in. When the Armalite AR-10B pattern mags I ordered arrived, they would not even fit in the mag well. now I have four AR-10B mags that are basically paperweights.

It looks like the next logical step is to either modify the PMAG to fit, or to try and cut the over-insertion stops out of the upper receiver. Since the PMAG is cheaper and made of plastic, I think I'll start there.

To summarize: screw this lower. Unholy mishmash of patterns. The lower mates perfectly with the Noveske N6 gen 1 upper, but the mag well takes LR-308 pattern magazines, which are incompatible with the N6 upper's over-insertion stops. While SMOS Arms is defunct, Stubborn Mule Manufacturing is still going, but they haven't responded to my e-mails.

[gunsmoke50]

Update:

Completed build. Required a DPMS bolt catch threaded pin. Also had to Dremel down the front part of the PMAG to clear the insertion stops. Have yet to test it on the range

[98Z5V]

Awesome update, man - I'll love to see this one running.  It's some very well-built hardware.  When it's running like a Singer sewing machine, you'll have to get the full parts list details in here.  I'm sure this one will come up again in the future.