I planned on doing this in a previous thread I had started a week or so ago but decided to start a new thread instead.  Many, but not all of the parts will interchange.  The parts that don't readily swap are close and somebody more familiar with both platforms might be able to fit parts with a little file and/or mill work.

The two rifles being compared are an early green 20" pre-ban and a recent E4 with 1.5x optic.  

First up, the Steyr and the E4


And the Steyr and the E4 with a Gen IV STG556 stock


The receivers.  The MSAR is on top



Underneath.  The Steyr is on top


The feed ramps.  MSAR on the right.


Front view of the Steyr



The MSAR



The bolt carriers.  Note the rougher casting marks in the MSAR part.  The MSAR has a plastic cocking piece and roller like a select-fire AUG.  




The bolts and firing pins.  The MSAR's bolt is chromed and the firing pin is spring-loaded.  The bolts themselves seem to interchange fine between both rifles.  The MSAR bolt sleeve will not fit into the Steyr bolt carrier.




MSAR bolt assembly in Steyr carrier.


Bolt sleeves.  MSAR on top.


Extractors and pins.  MSAR extractor on bottom.  The extractors aren't interchangeable between bolts.  The MSAR extractor is a little wider.  Also, the retainer pin is larger in diameter.



Thrust pieces.  The MSAR's are chromed.  Note the larger diameter on the MSAR parts.



Gas piston parts.  MSAR has four gas rings.



Gas regulators.  The MSAR has the dimpled rivet.  



Gas blocks.  The MSAR's surface texture is a little rougher.  The MSAR uses "S" and "H" for gas port sizes while the Steyr has a small dot and a big dot.



Slightly different location of the gas ports on the barrels keep the barrels from interchanging.  Note the flutes on the MSAR barrel.


Flash hiders.  Steyr part slotted all the way through.




Forward pistol grips.  The MSAR part has finger grooves and ridges.





Trigger packs.  The Steyr is green.  The MSAR pack will fit into the Steyr but the bolt release parts keep the Steyr pack from going into the MSAR stock.



Butt plate pins and butt plate.  The pins will fit fine in either rifle but the butt plates aren't interchangeable.  The MSAR is black.  Note that the MSAR pin doesn't have the intermediate slots so that the butt plate can be removed without taking the pin all the way out.




Finally, the Steyr in the MSAR stock.  


And now the AUG A3 and the STG-556!


Given the popularity of my earlier thread, I thought I'd post some additional photos.  These compare a Steyr AUG A3 with a MSAR STG 556.  Both guns are similar in set-up with square stock latches and railed receivers.  I removed the sights and slings since I wanted to compare the bare rifles themselves.

First up; magazines!
The AUG mag is the one with the green base plate and follower.  Mags will interchange between the two guns.  Both will drop free from the AUG but will not from the MSAR.





Barrels.  As with my pre-ban AUG, the barrels won't swap between either model.  The gas blocks are in a slightly different location between the two makers.  The breech ends are lined up in this photo.  Note the slight variance in gas block locations.
The AUG barrel has the black VFG:



Steyr barrel markings:


MSAR's barrel markings:



Both rifles together with magazines inserted:



Chamber areas.  The MSAR's chamber is beveled and recessed.  


Interrupted threads.  AUG on left.


Vertical grips.  Note the differences in the gas block.  



Muzzle devices.  AUG on bottom.


Gas blocks.  Both are "GR" marked.  Note the "S" and "H" marks on the MSAR.



Gas plugs and pistons.  The AUG's piston has three gas rings as opposed to the MSAR's four.  Plugs and pistons (and springs) will interchange between both guns.  The AUG's center rivet is solid.






The AUG's cocking handle and barrel latch.


Same stuff on the MSAR.


The AUG's side rail.


The MSAR's side rail.


Both receivers.


The AUG's feed ramps.


And the MSAR's.


AUG barrel interface.


And the same view of the MSAR.


Top and bottom views of both receivers.  Note the longer rail on the AUG.



Rear sling swivels, butt plates and takedown pins.  The MSAR pin has the QD swivel.  Pins will interchange between the two but the butt plates will not.  Note that the MSAR's plate is longer overall and is ribbed.




Trigger packs.  The MSAR pack is black.
Note the different methods used to lock the bolts open.  This keeps the packs from interchanging.





Bolt release levers.  The MSAR stock is green.



The AUG in the Microtech stock.  Perfect fit!  The MSAR will fit into the Steyr stock but there's a slight mis-alignment between the stock latch and the groove in the receiver.  It might fit but I didn't want to force anything.


Bolt carrier assemblies.  I think Steyr calls it a "slider" instead of a carrier.  Anyway, the MSAR's thrust pieces are chromed.  The left thrust piece is bigger than on the MSAR and can't be used to push out the gas piston.




Firing pins and bolts.  The MSAR's firing pin spring is silver in color.  These two parts will interchange (didn't check headspace!) but individual bolt parts will not.  I also note that the MSAR firing pin sticks a little inside the AUG bolt.  I believe it's dragging slightly on the AUG's cocking piece.





Bolt assembly parts.  The AUG is on the bottom.


Slightly different extractors.  The AUG is on the top.


Steyr bolt and firing pin in Microtech slider assembly.


Microtech bolt and firing pin in AUG.  No problems with bolt locking in smoothly but, again, I didn't check headspace.


And, finally, this guy.  

Excellent work!!!

nice, thank you for the pics and write up

this should be a tacked thread...

excellent resource for those wondering the differences internally btwn the two...MSAR's and actual Steyrs

really great work and thank you.

Thanks for taking the time to post this with all those pictures and descriptions of each. Great thread and should be tacked.

The bolt carrier is better than it was for the MSAR, but they still could be cast a little nicer. It would be nice to have the intermediate slot for the buttplate pin to stay in when removing it.

Receiver, bolt..just about everything on the MSAR is outstanding.  The wider extractor is nice. Four gas rings is nice.

MSAR can do barrels for the Steyr, but you've got to special order them through MSAR.

Excellent!

Great post OP. The only thing I like on the original A1 rifles over the E4 is the charging handle.

Gotta throw a big PLUS ONE on that!

Excellent and informative post!  I agree, this should be tacked.

+1


This was my AXR vs. AUG A3 thread:
http://www.ar15.com/forums/topic.html?b=6&f=43&t=278246

There was another MSAR/ AUG comparison thread not too long ago.

Someone should put them all together and tack it.

No photos but as an update; the stock latches are not interchangeable between Steyr and MSAR.  The MSAR part is a little shorter than the Steyr part.  I don’t know about the trigger and safety parts yet.

+1. Would make for a good tack.

Sorry steyr, MSAR make a better gun. Fit, finish and over all quality is superior on the MSAR.
Way to go for a GREAT AMERICAN company.
Higher quality at a better price with excellent customer service to boot.
Steyr, this is when you start to take notes.
Greg

How do the flash hiders compare in function?  Which one works better?  Over all it is easy to see the improvements made by MSAR.  Looking at the bolt carrier on my STG556 I would of never guessed it was cast?  That does not give me a warm fuzzy filling.

Let me be up front and say that I have a knee jerk aversion to anything cast, especially with regards to a firearm part.  That said, I think it's an issue that's more in the mind than in reality.  Ruger uses castings for everything.  There are thousands of older cast AR lowers out there.  Caspian and several other high cap 1911 frames are cast.  Yet if castings were so bad, we should hear and have pics of failures on a regular basis.  But we don't.

The only firearm that I know had serious issues, was forged and machined; the Williams aluminum FAL receiver from about eight or nine years ago.  That failed due to the aluminum not being able to handle the stresses without deforming in the locking shoulder.  I would think that cast Ruger revolver frames and all the cast Ruger autos and Caspian frames would have more examples of failure.

Oh...I forgot one...the venerable Browning Hi-Power is cast, too.

I think, and this is just me, that the cast vs. forged debate is largely overblown.  Now, if the parts were discovered to be MIM, then I'd have doubts.

Isn't there some guy making aftermarket charging handles for the MSAR (and USA Steyr?)?  What variant do the aftermarket ones resemble?

I understand that the STG556 has been well tested and is quality.  And after learning that the bolt carrier is cast I am still happy with it.  But given the choice.

Guys,

I'm not a manufacturing expert.  The bolt carrier could be machined from a solid block for all I know.  With that said, the MSAR bolt carrier has a rougher surface texture and more machine marks, etc than the Steyr part, that's all.

That bolt carrier may not be pretty, but it's built like a damn tank. That thing would be the least of my worries.

And when I run out of my stash of zombie tranquilizers, I can use it as a blunt force trauma weapon!

There was talk about it, but I haven't seen anyone offer anything as of yet...

I pulled the barrel off my E4 yesterday and installed it on our select-fire AUG in the armory.  The MSAR barrel fit and latched in nicely.  I didn't have a headspace gauge with me but as long as it headspaces, I don't see any reason why it wouldn't work properly.

interesting, thanks

Nice write up and great pictures, thanks for taking the time!

Thanks Hardshell.

+1 these should both be tacked....great job

are the hammers in the trigger assemblys made of plastic? first time i have seen that if they are plastic


great post by the way.

Yes, they're plastic.  The only metal in the hammer packs are the pins and springs.

Steyr has been making polymer hammer packs for the AUG since ~1977.  They have proven themselves in combat all over the world.  It's a non-issue.

Very interesting. I never knew the firing pin was that big.

Thanks

Pics added!

DOH!  We should have bought from Microtech!

That's just WAY too funny!

Thanks,
Lee

is a MSAR gen 4 closest to an AUG A2 with the optics rail?  Does the A2 have hold open?

All AUG's and clones have a last round bolt hold open.  What sets the MSAR's and the A3's apart is the bolt release. The A1s and A2s don't have this, but you can swap the stocks and hammer packs out to a MSAR or A3 and then you're all set.

And in your opinion what is the better of the two rifles pictured in regards to firing, function and durability?

I'd say that is gonna be a very subjective answer.  From a firing/function/durability side they are very comparable, and neither is really better than the other.  Really it comes down to what kinda mags do you want to use, or which name do you want on the side, etc....  From a functional/reliability standpoint you are not gonna find much difference...
 

Ah, well.  All good things must come to an end.