stabilize/unstabilize???

[billshamblin]

a 223 26" 9twist barrel will stabilize an 80 grain sierra match king with 25+ grains of varget but not with 23. "it will stabilize but you have to have a hot load." says the factory.

my question is, when the bullet begins to slow down more and more at longer ranger will it begin to tumble/destabilize or could the 80 smk make it all the way to 1000 yrds ?? my ballistics program says it still be going 1200+ feet/sec at 1000 yrds.

thanks, bill shamblin

 

[Forum Boss]

There are a couple different issues going on here. One is maintaining sufficient velocity so that the bullet doesn't go transonic before reaching the target. At 1200 fps you should be OK with that,but you don't have a large margin left).,Speed of Sound is 1107 in dry air at sea level, 50 deg. F)

See: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html

The second is whether the bullet is retaining enough rpm to remain stable at long range. That's determined by whether the bullet spins up enough while it's in the tube. That in turn is a function of twist rate, bullet design, AND the velocity with which the bullet is pushed through the rifling.

If you call Sierra, they can probably tell you how many revs you need to keep the bullet stable. Basically this will let you know the minimum acceptable muzzle velocity given your twist rate,revs are a function of speed AND twist rate). And keep in mind that there can be small barrel to barrel variations. E.g. your "9 twist" may really be a 1:9.2 or 9.3.

 

[billshamblin]

thanks. i understand that. here is the question. lets say my barrel will stabilize the bullet when driven fast out of the barrel with a near max load and it does not tumble for 100 or 200 yrds and makes good sub-moa groups. all that is proven true.

is there a way to predict if the bullet will tumble before going subsonic without just trying som 1000 yrd groups? the load/bullet is chosen to stay supersonic at 1000 yrds but i didnt think about the spin the only place i can shoot 600 or 1000 yrds is at MATCHES and i will feel pretty stupid if i miss the target entirely oir keyhole because my bullets tumble.

i know the 223 isnt an ideal 1000 yrd caliber but i enjoy the challenge of shooting it at 600/1000 yrds if possible. what do you think??