So I ran into one of smartest guys i know about shooting.Franco Special, 1:12 Krieger barrel. Match Monster / blem Nosler CC's. Varget. Pushing them a bit harder than 2700.
He must remeber every conversation as he starts asking me all these questions about my 308 build. Thats the last time i seen him. Been a while.
After a few minutes he says , what barrel did you go with .
Criterion 1/10. Very good choice he says. i go on to ask about why the shift to 1/12 twist for the 155s.
Ahh he says, now some real questions.
See what happens is there is a thresh hold that if pass it your bullet will either self destruct or not stabilize.
Then he goes on
"Start with bullets. If they are not made well the faster RPMs will show up any defects in centrifugal forces applied.
If the bullet core is not quality and the jacket not uniform and they are not put together well the faster the RPMs the more the bullet will not fly well."
Now he says the end use is a key factor.
"As you know from shooting all kinds of shit through your rifle from cast to light fmj's you can get good accuracy from 1/10
1/10 covers a lot of ground because of "velocity" most folks and guns for that matter with 30 cal are going to be running between 2400-2700 fps. now get into bench rest and long range 1000 yard shooting you need velocity to hang on outto the target. Push a marginal bullet to 3000fps in a 1/10 well it might just self destruct like M193 and cheap 223 can do in a 1/7 vs 1/9"
"We also know from testing the higher RPM equates to more damage to the target be it mammals of such intended. ( he never says humans/enemies )"
in the end he basically says " with the common 30 cal battle rifles of 20-24" barrel your not going to get those higher velocities anyway before you get to those loads pressing the limits of your platform especially the semi autos.
Now hes says "with out going home and getting specifics I can tell you your average 308 bullet from 150 to 175s are generally going to have a sweet spot between 145,000 rpm and 175,000 fps how you want to get there with velocity or barrel twist is what you need to figure out. "
He says in the end "You need to run what you brung and try stuff. We had data that would say this combo will shoot and when put down range it does not"
Muzzle velocity X 720 / twist rate in. will get you your RPM.
for example your 155 load at 2700 fps with a 1/12 = 162,000 rpm < look at that right darn in the middle of that old mans BS words.