im going to be shooting 50-300 yards out of a 16" barrel what twist should i have?
is this correct?
1:10 40-52
1:9    52-62
1:8    62-75
1:7    75-80+

would my accuracy suffer some if i shoot 55 grain out of 16" 1:8 at 100 yards?

yes

yes to which question?

Quoted: im going to be shooting 50-300 yards out of a 16" barrel what twist should i have? is this correct? 1:10 40-52 1:9    52-62 1:8    62-75 1:7    75-80+

The above is a decent rule of thumb... but there are no guarantees for what will and wont stabilize.  For instance, several people here can shoot 77gr SMK's out of their 1:9 16" carbines without issue.  That's pushing the limits though.

For stabilization... I'd edit the chart to be like so.... and keep in mind these are generalities:

1:10 40-55
1:9    40-75
1:8    45-80
1:7    55-100

There are also no guarantees on whats going to be most accurate.  If you are going to only shoot out to 300yds.... then 55grainers will do nicely.

For example... I have a relatively "tight" 1:8 20" barrel, that shoots 77gr SMK's the best.  2nd place goes to 45gr varmint bullets.  So a light bullet in a tight twist cannot be assumed to be "overstabilized" (whatever that is).  As long as the bullet does not fly apart in flight (some 40gr in a 1:7 might) then it might be an excellent match.

would my accuracy suffer some if i shoot 55 grain out of 16" 1:8 at 100 yards?

Absolutely not!  Again, each barrel (even from the same vendor, and same manufacturing run) will have a bullet it "likes" and you have to play with them to see.

What is WAY more important than the weight of the bullet, is the overall quality of the bullet projectile, power, primer, and consistency of the power charge, and case.  Almost any rifle will shoot better with quality match ammo with a less desireable bullet weight.... than cheap ammo with the "perfect" bullet weight..... as long as the bullet is stabilized.

thanks for the help
my Ar build will be
oly 16" sum fluted 1:8
6 position tele stock
2 stage trigger
first samco tactic grip
phantom 5 port fs
a2 forged front sight
uninterrupted FIRSH
buis

compact 3-9 illuminted bullet drop scope
fore grip
maybe bipod

That 1:8 SUM is gonna be SWEET.

Now go get you some Black Hills 77gr SMK blue box and be done with it!

What 3-9 scope are you talking about?

hammer or ncstar

i know its not great, but after the rifle i wont have much left ill have to upgrade the scope later

btt

Quoted: btt

Once brouhaha chimes in... I doubt there is much need in getting any other opinions.