1:9 twist ?
- Thread starter sgreen3
- Start date
Turbulent Turtle
F-TR competitor
It also depends on the barrel length and what kind of 1:9 twist you have. Some 1:9 twists are closer to 1:9.5 or slower.
jonbearman
I live in new york state,how unfortunate !
Load up a few rounds and try them.Dont think it wont work when it probably will. I shoot the 68 and 69 grainers out of one of mine and even though the 75's work,I get better accuaracy with them myself.
Follow up to my 7/4 post: I came across a box (you only get 50!) of 77g SMKs that I'd bought about 10 years ago and forgotten. Just for grins, I decided to load 'em up and see what happened, expecting little more than patterns from a 9" twist (the box says 7" or 8" twist only). I picked BLC-2 from the powders on hand, as it was supposed to give about the top velocity with this bullet, and loaded up some 3-shot sets in 0.3g steps from bottom to top of the Hodgdon chart. These were just seated at 2.260 OAL, "magazine length". Shooting was from a concrete bench, with a bipod and rear sandbag.
To my surprise, the groups ALL came in at 0.72 minutes or less (at 200 yards), with one powder charge at 0.14 minute (a 3-leaf clover). I went back a few days later with some more 3-shot sets at 0.1g steps either side of the tiny group, and while none of 'em shot quite that small, they went from 0.27 to 0.44 MOA over a 0.4g range of powder charges, again at 200 yards. I plan to get some more of these bullets and do some experimenting with seating bullets longer, and I'll probably try Varget to see if I can get equivalent groups and less temperature sensitivity. Although I don't know how much better I can really expect to do.
While Sierra 69g SMKs and Berger 70g VLDs will shoot groups that small, I think I'll be better off shooting the 77 grainers in 600 yard F class matches. So it was a delight to find how well they work in my barrel.
To my surprise, the groups ALL came in at 0.72 minutes or less (at 200 yards), with one powder charge at 0.14 minute (a 3-leaf clover). I went back a few days later with some more 3-shot sets at 0.1g steps either side of the tiny group, and while none of 'em shot quite that small, they went from 0.27 to 0.44 MOA over a 0.4g range of powder charges, again at 200 yards. I plan to get some more of these bullets and do some experimenting with seating bullets longer, and I'll probably try Varget to see if I can get equivalent groups and less temperature sensitivity. Although I don't know how much better I can really expect to do.
While Sierra 69g SMKs and Berger 70g VLDs will shoot groups that small, I think I'll be better off shooting the 77 grainers in 600 yard F class matches. So it was a delight to find how well they work in my barrel.
Yes, a 1:9 will stabilize 75/77gr tangent ogive (read: non-VLD, AR mag length friendly) bullets just fine - be it from a 16" or 30" barrel.
Now, will such a barrel shoot 68/69s better? Maybe - just depends.
I had a 26" 1:9 Savage 223 and it shot the Hornady 75gr HPBT much better than 68gr HPBT; never tried 69 SMK/CCs but with the 75s shooting sub-half MOA there was never a reason to.
Now, will such a barrel shoot 68/69s better? Maybe - just depends.
I had a 26" 1:9 Savage 223 and it shot the Hornady 75gr HPBT much better than 68gr HPBT; never tried 69 SMK/CCs but with the 75s shooting sub-half MOA there was never a reason to.
Lotsa good info here but most are forgetting an important point and that is how fast are you going to push the bullet??? The twist/bullet relationship is quite a bit different for say a .223 vs. a 22-250 Ackley!
To make my point; My 9 Twist 22-250 Ackley stabilizes a 80gr Berger VLD prefectly at 3325 fps! Wouldn't happen with a .223!
To make my point; My 9 Twist 22-250 Ackley stabilizes a 80gr Berger VLD prefectly at 3325 fps! Wouldn't happen with a .223!
I keep track of the RPM needed to stabilize a given bullet. When You know that and how fast You can push it, It's just some simple math to determine what twist rate is required!
Over time, I've come up with the following required Rpms on certain 22 cal bullets:
Hornaday 52gr Amax = 155,000 RPM
Hornaday 53gr Vmax = 205,000 RPM
Hornaday 75gr Amax = 220,000 RPM
Hornaday 80gr Amax = 235,000 RPM
Berger 75gr VLD = 240,000 RPM
Berger 80gr VLD = 263,000 RPM
Over time, I've come up with the following required Rpms on certain 22 cal bullets:
Hornaday 52gr Amax = 155,000 RPM
Hornaday 53gr Vmax = 205,000 RPM
Hornaday 75gr Amax = 220,000 RPM
Hornaday 80gr Amax = 235,000 RPM
Berger 75gr VLD = 240,000 RPM
Berger 80gr VLD = 263,000 RPM
Turbulent Turtle
F-TR competitor
ewspears said:
For which velocities?
My Old Math skills say you use the velocity to determine the rpm:
1. Divide your twist by 12 to get feet/revolution
2. Divide bullet velocity (ft/sec) by (1) above (ft/rev) and you get a number in revolutions/second
3. Multiply (2) by 60 to get revolutions/minute.
Example: A 9" twist barrel gives 9/12 or 0.75 ft/rev. A bullet going 2700 fps from that barrel is spinning 2700/0.75 = 3600 revs/sec. In 60 seconds that's 216,000 revolutions (per minute.)
If you need a particular rpm, you can work backwards to the velocity needed to achieve it:
4. RPM needed divided by 60 gives revs/second.
5. Revs/second times feet/rev (from 1 above) gives feet/second.
Example from ewspears's list - you need 240,000 rpm to stabilize a 75g Berger VLD. That's 4,000 revs/second. If you have a 9" twist barrel that's 0.75 feet/rev, times 4,000 revs/sec = 3,000 fps needed to get the desired spin rate.
Again, this is old math. Maybe things have changed in the half century since I studied this stuff - everything else has.
1. Divide your twist by 12 to get feet/revolution
2. Divide bullet velocity (ft/sec) by (1) above (ft/rev) and you get a number in revolutions/second
3. Multiply (2) by 60 to get revolutions/minute.
Example: A 9" twist barrel gives 9/12 or 0.75 ft/rev. A bullet going 2700 fps from that barrel is spinning 2700/0.75 = 3600 revs/sec. In 60 seconds that's 216,000 revolutions (per minute.)
If you need a particular rpm, you can work backwards to the velocity needed to achieve it:
4. RPM needed divided by 60 gives revs/second.
5. Revs/second times feet/rev (from 1 above) gives feet/second.
Example from ewspears's list - you need 240,000 rpm to stabilize a 75g Berger VLD. That's 4,000 revs/second. If you have a 9" twist barrel that's 0.75 feet/rev, times 4,000 revs/sec = 3,000 fps needed to get the desired spin rate.
Again, this is old math. Maybe things have changed in the half century since I studied this stuff - everything else has.
bayou shooter,
For any reasonable velocity! It just means that is the barrel exit RPM required and it matters not whether it comes from a medium twist bbl at a high velocity or a fast twist bbl at a medium velocity!
Example: The Rpm would be the same; of a 1:12 twist bbl at 4000 FPS Velocity as a 1:9 twist bbl at 3000 FPS Velocity!!! RPM in both cases would be about 240,000 RPM!
For any reasonable velocity! It just means that is the barrel exit RPM required and it matters not whether it comes from a medium twist bbl at a high velocity or a fast twist bbl at a medium velocity!
Example: The Rpm would be the same; of a 1:12 twist bbl at 4000 FPS Velocity as a 1:9 twist bbl at 3000 FPS Velocity!!! RPM in both cases would be about 240,000 RPM!
Turbulent Turtle
F-TR competitor
That's not what I meant.
The reason we need to statically stabilize bullets by spinning them is to counter the overturning forces produced by air resistance. Air resistance is directly proportional to the velocity of the object traveling through it; the faster it goes, the greater the air resistance and overturning forces and so on.
So, increasing the muzzle velocity of a bullet increases its spin induced by the twist in the barrel and using higher velocity you stabilize a bullet going through a barrel with insufficient twist, but there is a limit to how much you can make up before the bullet becomes unstable due to higher resistance.
So, my question is: what is the velocity range for each of those spin values?
The reason we need to statically stabilize bullets by spinning them is to counter the overturning forces produced by air resistance. Air resistance is directly proportional to the velocity of the object traveling through it; the faster it goes, the greater the air resistance and overturning forces and so on.
So, increasing the muzzle velocity of a bullet increases its spin induced by the twist in the barrel and using higher velocity you stabilize a bullet going through a barrel with insufficient twist, but there is a limit to how much you can make up before the bullet becomes unstable due to higher resistance.
So, my question is: what is the velocity range for each of those spin values?
wrangler5,
Glad to see You've got the concept down pat!
There is a little simpler way to explain and think about it! Use the 12 twist as a baseline since with a 12 twist you only have to multiply the velocity by 60 to get the RPM! For other twists, You just need to ratio the twist bact to the 12 twist. ie. For a 9 twist it would be 12/9 (RPM) 60 = RPM
Glad to see You've got the concept down pat!
There is a little simpler way to explain and think about it! Use the 12 twist as a baseline since with a 12 twist you only have to multiply the velocity by 60 to get the RPM! For other twists, You just need to ratio the twist bact to the 12 twist. ie. For a 9 twist it would be 12/9 (RPM) 60 = RPM
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