The older version of the SPS TAC has 1:12 twist. I have shot 175's FGMM through it out to 300 with decent results. They heavier bullet (SMK) doesn't shoot as tight in my rifle...it prefers the 168 SMK.

The newer SPS TAC AAC-SD is 1:10 and is basically made for the 175gr SMK.

As to the spam..... ..n no idea

 

The older version of the SPS TAC has 1:12 twist. I have shot 175's FGMM through it out to 300 with decent results. They heavier bullet (SMK) doesn't shoot as tight in my rifle...it prefers the 168 SMK.

The newer SPS TAC AAC-SD is 1:10 and is basically made for the 175gr SMK.

As to the spam..... ..n no idea

The ablsolute "Optimum" twist rate for a 175 gr bullet in .308 is 1:11.25. 1:10 and 1:12 do just fine.

What's probably happening in your newer rifle is there is a different set of barrel harmonics and it prefers the lighter bullet.

Do you have a muzzle brake on the AAC or just the thread protector? Differences in weight can make a difference believe it or not.

Those of us that hand-load, and avoid factory ammo like the plague, can tune to the peculiarities of the barrel. (Just an unabashed plug for the benefits of handloading )

 

I have the 700 heavy contour varmint 26", 1:12 and have good results with Sierra MatchKing 180gr. I use H380 44gr. Not a real fast round (2507 fps), but accurate and stable to 600 yards. I shot a 506 6x in my first F class shoot with this combo.

Just my gut feel, but I think a lot of reloaders have problems when they try to push 'em too fast. I don't think high velocity always yields accuracy. My 2 cents.

 

Just my gut feel, but I think a lot of reloaders have problems when they try to push 'em too fast. I don't think high velocity always yields accuracy. My 2 cents.

You are dead on. Only time one should worry about more speed is if the range is extreme and you're trying to keep the bullet above the transonic zone before it reaches the target.

I find that 2550 or so is "perfect" for my 175 gr BTHP's at the range I shoot at. Why punish the brass, bolt lugs, or burn up the throat unless it's absolutely necessary.