This was another owner shooting, a sample of how his rifle performed with 175s.

 

I had not seen this. Thanks for posting it.

 

i'm guessing they chose 1:12 because it works great with typical ~150gr military ammo, without the higher pressure or increased barrel wear of a higher twist rate.
the MK20 SSR was built for a specific purpose, and the guys out on the battlefield don't have the luxury of using hand loads or the latest factory offerings.

whether you believe FNH should have deviated or changed this when they released the "civilian version" of the SSR is probably a personal thing, depending on why you chose this specific platform.
if you bought a 20S to test its limits (and perhaps try to exceed what it was designed for), you might be disappointed.
if you bought a 20S because you wanted the most reliable platform for sending large quantities of lead far downrange with speed and decent accuracy, using readily available lower cost ammo, you're probably happy.

in the end, the .308 cartridge is going to have it's limits when going against newer calibers and bullets designed specifically for ELD shooting, and ultimately the answer for folks wanting to reach out farther is going to be swapping the barrel for one of these options.

i have already seen a couple of 20S rifles converted to a 6.5CM barrel.

 

I really like the 175gr for my long range shooters. While the 168gr are really good, I get just as good if not better results with the 175gr SMK.

 

I have found that the 168's are coming out of supersonic speed at about 800 yards and start doing weird things, I have several targets from 1000 yards that have "Keyholes" but the 175's don't do that at 1000. Your Mileage may vary !!! SCAR'd Mike - US Army 1974 - 1977

 

this guy also confirmed the 20" 1:12 barrel will handle the 175gr BT pill just fine.

https://www.thetruthaboutguns.com/gun-review-fn-scar-20s/

The 20S features a 20-inch heavy profile barrel with a 1:12 twist. How do you know the twist rate? It says so, right on the barrel. For those of you on the nerdier end of the spectrum, like me, that’s very helpful.
A flip through Brian Litz’s Ballistic Coefficient and Stability data shows us that a 1:12 twist rate will stabilize a 175gr Sierra Match King bullet even under the worst-case scenario with a Miller Stability Factor of 1.48. In other words, even if you’re at sea level with 0% humidity, it’s wicked cold out, and your bullet is only leaving the barrel at 2,600fps, the round will spin just fine. If you ever actually find yourself in that situation, I recommend you pick up your rifle and leave.
However, bullet shape plays a big role in stability. Bullet weight is the biggest determinant of bullet shape. That is, a light bullet will necessarily be a short one, and heavy bullet a long one. Still, there’s a lot to play around with there. For instance, even though it’s much lighter, that same 20S 1:12 barrel will only stabilize the Lapua 155gr Scenar bullet under the most ideal conditions. The moral of this story: know your bullet.
...


FN promises minute of angle accuracy from the SCAR 20S. Twenty years ago that would have been a high bar for an auto-loader. In 2018, it’s not any more. In fact, I’ve reviewed quite a few auto-loading rifles that will shoot 1 MOA or better. Fortunately, the SCAR 20S clears the bar easily, and bests it handily.

I shot several commercial loads through the 20S, and not a single one of them above 150grains shot as bad as 1MOA. IMI’s 175gr BTSP round averaged 3/4-inch five-round groups over four-shot strings. Black Hills 175gr Match did the exact same. Match grade ammo definitely shines in this rifle.
These are standard military 7.62 NATO long-range rounds, and I’m sure they’re the bullet these guns were built around. I shot several hunting rounds from Hornady, Federal, and Nosler, and they all scored around the 3/4-inch mark. The only round to hit 1 MOA, and it hit it dead on, was that 125gr Hornady Custom Light reduced recoil round.

 

so i did a bit more research and what i found and was told by one vet that was deployed with a MK20, the 175gr SMK was bullet for the std M118LR ammo issued for this platform.

 

Specifically the Sierra Match King 175gr.

 

I just updated this thread with my findings after trying about 10 match loads from different manufacturers.

Long story short, the 175 grain Sierra Match King projectile in the Federal Gold Medal Match load is pure magic in my 20S.

If you haven't tried the 175 SMK, you owe it to yourself to buy a box.

-Blake