twist rate

yes 1:11 means 1 revolution in 11". the weight of the bullet is the major factor in rate of twist. the 223 has a pretty wide range of weight so if the rate of twist is 1:9 the heavy bullets won't shoot as well as from a 1:10. i believe i got that right. front stuffers are like 1:24. there are a lot of factors that go into it BC, weight, speed, pressures, play a role in choosing a rate of twist but its easier to choose a bullet to match rate of twist than the other way round.

Twist rate selection

I don't remember the formula but there is one to calculate the optimum twist rate for a cartridge.

I takes into account the speed of the bullet, its length, and its diameter.

I do remember for example the magic twist rate for a 30-06 is something like 1 in 10 is you are pushing a standard 180gr lead core bullet at 2700fps. A solid non lead core bullet would be longer and then the optimum weight of this non lead bullet would be a lighter weight.

This then changes with something like the .223 using a 1 in 7 twist for the long 62gr at 3100fps. The shorter/lighter 55gr wants 1 in 12 at about the same speed.

Look at the various web sites for bullet manufactures and I think you will find the true formula.

Depends on the caliber and load. The twist rate is part of what determines the accuracy. That is why you find what ammo your gun shoots well. (I think)