So I bought a mud nato stock probably over a year ago.
Ordered a pair of matching grips for my two barrels from Steyr shortly after.

The stock was new & still had the hump on top.  I currently had a A3 in a black nato stock & recently bought a second black nato stock at a great price to paint.  So I did not even try out the new mud colored stock & just put it away.

Well I finally picked up a second A3 AUG.  Tonight I ground down the hub & proceeded to try both receivers in this stock.  At first it was a very tight fit & noticed some areas of the plastic needed to be cleaned up - the round nub on the front of the stock that is near the barrel takedown button.

Well even after everything it seemed like I still could not get either receiver back far enough to engage the receiver lock.
After looking at every angle inside the stock looking for possible obstructions I finally pulled the reciver lock from the stock.  Still not able to engage the lock.  It wasnt until I actually compared the lock to the other stock did I see the size difference.  After searching I could not even find a mention of different size locks until I looked under full auto differences.

So is there anything I can do to use semi receivers in this stock?  Not going to modify the receivers.

Two problems related to compatibility. 1. The receiver lock in the FA stock is larger than the channel of the semi auto receiver. 2. The guide rods on the FA stock are a larger diameter than the semi auto carrier. A semi carrier won't work in a FA stock. One could modify the lock, but Steyr will not sell semi guide rods - used guide rods can't be swapped from one stock to another either.

Then there's the issue of what the ATF would think about modifying a FA stock for use with a semi receiver. None of this would apply if you have a registered sear/hammer pack though.

I am running a NATO for mine. Removed the nub also. Mine fit fine. You have to use the NATO trigger pack.
https://m.youtube.com/watch?v=OcPjPQM5phw

I was worried about that Maleante.  After studing the locks it appeared that I could get a channel milled into it to fit the receivers.  But the guide rod issue.  There is no way to switch the guide rods?... Actually just tried just the carrier in the stock & nope wont work.  And looks like the rods are pinned in (I originally thought they were screwed in.)

Wow how the hell did I get a new production mud colored nato full auto stock?  That sucks & I am pretty sure I am stuck with it.  There is not many potential buyers I would think.

Pics to illustrate my problem:

See I never understood that. So I can modify the stock (or specifically, the receiver lock) and than an unmodified FA hammer pack will go right into it. So if I'm only going to have one registered part, wouldn't it be the receiver lock?

Or could I Form 2 an unmodified hammer pack and mod only the receiver lock? Seems like that wouldn't be ok.

Whomever you bought it from probably doesn't know they sent you a FA stock. If it were me, I'd let them know, you might get the correct stock...

The guide rods are like giant rivets. The rods are set in place and the most rearward end is flared to lock it in the stock. It's not a process easily done.

I thought the guide rod diameter was only different on early 900 series guns.