For my AWB crappy state the choice was simple for me, SIG, since the STG can't take STANAG mags. I really like the bullpup design but I do find mag changes very odd which would still be my hesitation if I could get 30 rounders for it here.
However, Tactical Product Design has built a beautiful AUG clone, the AXR, which does take STANAG mags! The only downside is they simply can't meet the demand and are on quite a long backorder. If I were able to walk in to a shop and have both the SIG and the AXR side-by-side it would have been a much tougher choice. I still think I would have gone with the SIG simply because it's a platform I'm more comfortable with, but I know I'll be getting an AXR in the future (the ARFCOM answer is always "get both"!)
Here is some comparisons between the SIG and the MSAR...
SIG556
Pros
- High availability
- Familiar design
- Takes the standard STANAG AR mags
- AK-style action, piston driven, extremely reliable
- Excellent factory trigger
- Ambidextrous safety
- Great barrel, very accurate right out of the box (with the right ammo)
- Integrated BUIS
Cons
- Base model is fairly expensive
- Lacks aftermarket addons, expensive to upgrade
- Base handguards make the rifle pretty barrel heavy
- Some QC issues with the front rail being loose
- Forward take-down pin is poorly designed (double screw heads), aftermarket pin is highly recommended
Other Info
- Being a 1/7 twist barrel, some people have had issues with shooting 55 grain XM193 style loads which may hurt your pocketbook since it's definitely cheaper than buying M855 / Mk262. However, it shoots Mk262 and the M856 tracer beautifully while gobbling M855 without any hiccups.
- For states with an AWB, your FFL will have to pin the stock and remove the flash suppressor with a break and weld it. This adds to the base cost.
MSAR STG
Pros
- Bullpup design, very compact
- Integrated optic option nice for an out of the box, ready to go rifle (although most buy the flattop to save money and get glass they want)
- Integrated BUIS
- Short-stroke, gas-piston operating system; very reliable and clean
- Barrel swap is awesome and easily accomplished with a simple release and twist system
- High availability
Cons
- Mag changes awkward due to the bullpup design; training may overcome this
- Takes proprietary mags
- Expensive out of the box
- Moderate complains about feeding issues, YMMV
- Very few aftermarket accessories available (much less than even the SIG)
Other Info
- Twist rate for each barrel: 1/7 -> 14", 1/8 -> 16", 1/9" -> 20" and 24"
- Optics attach fairly high compared to the SIG above the bore, haven't had any issue in my limited time with it, but may be a concern to some
- Coming soon will be a NATO compliant stock which will take the STANAG mags.
To me the AUG is sexy, cool, and is on my "to-buy" list, but it's more of a range toy to me than an actual field rifle. Either will treat you well, and if you happen to have a few AR platform rifles than the AUG becomes very attractive. For me, I was looking for something more along the lines of a SHTF gun which is why I went with the SIG. You have to ask yourself what you want out of your rifle and the choice will become clearer.
Enjoy whichever you choose!