Before anyone thinks I am recommending something that might damage the receiver, I want to cover a little bit of my background, and then go through the technical issues involved with removing the top rail.
For those that don't know, I have a Masters degree in Architecutre and have taught Materials and Methods courses and General Engineering course at the University of Illinois School of Architecture and Engineering Schools. I am not some guy just hocking my wares for a dollar and telling you to do something with no regards the the consequences, but rather I do actually have a bit of knowledge when it comes to this sort of thing.
The receiver of the Steyr AUG A3 is 7075 aluminum with a T6 heat treat. For those who are not familiar a T6 heat treat is accomplished by heating the entire receiver to 925 degrees farenheit for an hour. There are actually a few more steps in the process, and differences to the process depending on size of the parts, etc, but the point is you are heating to over 900 degrees farenheit for a good length of time.
We recommend using the torch for a total of about 30-60 seconds total on the areas with the bolts, moving it around so as not to heat a single point.
You will note when doing this that the WHOLE RECEIVER gets too hot to touch. Why? Because aluminum is VERY thermally conductive.
What this means is that the heat you apply will quickly dissipate throughout the entire receiver.
The ability to heat any point of the receiver to where you would create issues with the heat treat would, quite honestly, take some intentional, concerted effort! Steyr themselves recommends in the manual to use a torch to break down the loctite as already mentioned.
Another way to think about it is like this - you have a steel barrel getting up to 400-500 degrees farenheit when firing an AUG fast and hard. That heat from the steel barrel is going to go right into the receiver due to the thermal conductivity of the aluminum, but the receiver doesn't fail...and Steyr design the gun with an aluminum receiver this way from the outset. Same with an AR-15, your upper and lower are aluminum, and the upper has the chamber of the barrel completely surrounded by aluminum where the barrel is attached via threads in the aluminum. Ever heard of an uppers aluminum threads giving out before a barrel or gas tube burst?
In any case, the point is that the quick heat of a propane torch should be completely fine on the receiver. Now if you want to give it a try with the 4mm allen wrench we include and use a pair of vise grips attached to the end to see if it will turn, go ahead and give it a try! The worst that can happen is they won't turn (well, you could strip out a hex head on a bolt, so don't overdo it!)
In our experience of the two receivers we did it on the bolts would not budge and we were risking stripping out the hex heads on the bolts. Per the manual, a little bit of heat losened up the loctite and the bolts came out with a little force to break the remains of the loctite.
Our other concern is clamping of the receiver to get enough force to turn the bolts without breaking down the loctite- it is very difficult with the shape of an AUG receiver to clamp it properly without risk of it slipping in the clamp while you apply a good amount of force. Quite honestly, I don't want to see anyone get hurt or bust a receiver if the receiver or a tool slips in the process. In my professional opinion, a little heat to break down the loctite is the much safer way to do it unless you have special tooling that allows you to clamp the receiver securely.
So there you go. If anyone has any concerns please let me know, but in any event, you should be fine with a little heat to break down the loctite.
Sven
Manticore Arms