Stability factor...

Been playing with the stability calculator and from what I understand you want to be at 1.5 for optimal performance. 1-1.49 is considered marginally stable and anything less than 1 supposedly keyholes. So let's get down to the numbers. Say a guy has a 223 with a 12 twist. Theoretically should stabilize up to the 60g vmax and the like with no issues. My bullet of choice is the 53g VMAX at 3350fps. Recommended minimum twist rate is 12" The stability factor is .99 So with that said it still shoots nice 5 shot 1/2 MOA groups at 100 yards. So that got me thinking that's a long ways off the 1.5 recommend. So I put the 50g vmax in at 3450fps and again the stability factor is only a 1.15 Again these shoot 1/2 MOA 5shot groups at 100 yards. So my question is how do you even achieve a 1.5 stability factor in a 223 with varmint weight bullets and a varmint twist rate? I even put the little 40g VMAX in at 3800fps and its showing a 1.34 stability factor. Still a ways off the recommend 1.5 and that's a 40g bullet from a 12 twist at 3800fps...why are these still all shooting 1/2 MOA with ease at 100 yards if they're marginally stable at best? What am I missing?

Another example being my 240 wby with a 10 twist shooting 87g vmaxs at 3500fps. It shows a factor of 1.47 which is pretty close to the 1.5 recommended. It shoots 1/2 MOA at 100 yards.

You're either forgetting to input something in the info, or using a calculator that isn't asking important questions that matter in stability such as actual bullet length. All those bullets should be good to go in a 12 twist and how your gun shoots them verifies that.

Using your info, I'm getting 1.350 for the 53 v-max, 1.6 for the 50 v-max, and 1.950 for the 40 v-max.

The 87 v-max in the 240 wby at that twist and speed is 1.7.

From what I read 1.3 to 2.0 is in the optimal range. You can get down close to 1.0 and still not really see big effects at reasonable ranges. Military tries to stay right in the middle at 1.5.

Bullet length is the most important factor, more so than bullet shape or weight.

JD338

ShadeTree- Which program are you using for those numbers? I'm using the one off Bergers website and I think I entered everything correctly, down to bullet length, since I have all the bullets on hand. Even if a guy doesnt have them on hand, JBM have bullet lists with the lengths. And my strelok pro program will calculate your stability factor as well, and it's very close to what the Berger site is showing too. Your numbers are all a bit higher, which I'm just curious how you came up with the numbers? This is the info for the 223/53vmax in the Berger program and I still get under 1 everytime...

And here is the strelok pros calculation, which gives a .97

While it is fun and interesting to delve into the numbers, sometimes I think we go too far down the proverbial rabbit hole...
If the bullet/load combination is shooting well in your rifle, or as in your case, very well, I would say do not worry too much about it. Shoot those nice groups, harvest varmints efficiently and have a great day!

Heres the 240 info from berger

The 240 wby info from strelok pro...1.37

I use the JBM calculator. It covers all the bases and asks bullet length, and tip length. Tip length is counted, but not on a 1 to 1 scale of the total bullet length. Your barrel does not have to work near as hard to stabilize a near weightless thin plastic tip added onto the end, as it does the actual length of the weighted bullet. Tip length is listed for the 53 and the 40 v-max, I used the same length for the 50 as is listed for the 53.

On the 240 wby, 87 v-max, I used a conservative tip length of .100. Actual tip length is likely longer than that which would make the stability factor higher yet.

In my 7-300 I have a 9 twist...the bullet I want to shoot is the 180 eldm and it recommends an 8" twist. But I am right at 1.5 for the stability factor so it should work. I haven't shot any of these yet.

Blkram":3etysjez said:

While it is fun and interesting to delve into the numbers, sometimes I think we go too far down the proverbial rabbit hole...
If the bullet/load combination is shooting well in your rifle, or as in your case, very well, I would say do not worry too much about it. Shoot those nice groups, harvest varmints efficiently and have a great day!

Click to expand...

Agreed. I've messed around putting numbers into a stability calculator already just out of curiosity sake, but never bothered seeing what a 150 Partition comes up as for example in a 308 or 30-06 twist. I already know they're gonna work regardless of what a calculator might say.

Only time I used it for real was when figuring out which bullets out there might work in a 14 twist 250 savage, as the choices of viable hunting bullets that are short enough to work are limited.

And strelok plus shows a 1.46 so pretty close to the Bergers calculation.

Thanks for the info ShadeTree, appreciate it. Guess I'll just keep shooting them then and not worry to much about it.

I typically use it as a reference and not the gospel. If I'm close to a decent stability factor and they shoot good groups I run it down range and see if the BC matches up. If it doesn't match up but shoots good groups down range I just adjust my numbers to match what I'm seeing in the field and let them fly.

I have never really bought-into this "marginally stable" range of 1.0 to 1.5 !!!

Seems to me once a bullet is stable it stays stable.
So as velocity decreases does a bullet become less stable?

JD338 is right on... bullet length most critical. Elevation can have a significant effort too. Velocity of projectile doesn't matter as much as some people think. Try some of the variables in the calculator and you ll get a flavor of what matters most.

And, as mentioned earlier, some combo s show marginal stability and shoot like a house afire... go figure!

Would you believe my S2 Vanguard in 240 WB with a 10 twist shoots the 105 AMax 1/2 MOA at 3200 fps? I tried it at a friends suggestion thinking I was set to fail... shot a 1 3/8" group at 300 yards and nice clean bullet holes in the paper. Would of never bet on that.

I would have never thought your 240 with a 10 twist to shoot the 105 amax...That wouldve been my bullet of choice, but I figured no way in hell my 240 vanguard with a 10 twist would stabilize it. Guess I'll have to buy a box now and see what she does!

ShadeTree":7bx7z4ds said:

I use the JBM calculator. It covers all the bases and asks bullet length, and tip length. Tip length is counted, but not on a 1 to 1 scale of the total bullet length. Your barrel does not have to work near as hard to stabilize a near weightless thin plastic tip added onto the end, as it does the actual length of the weighted bullet. Tip length is listed for the 53 and the 40 v-max, I used the same length for the 50 as is listed for the 53.

On the 240 wby, 87 v-max, I used a conservative tip length of .100. Actual tip length is likely longer than that which would make the stability factor higher yet.

Click to expand...

I just measured a 53gr V-Max and the jacket & lead portion is around .70 and tip length is .13
I ran some of my 53gr V-Max over Magnetospeed and my .223 Rem is 3530FPS a little faster.
I ran it at Bullet length of .72 slightly longer than .7 jacket and lead portion, but who know if this is correct.
This load in my Rifle shoots three 5 shot groups average of .77 inch at 200 yards.
My Rifle is a Remington 700 VSII with 26 inch barrel.

Nice! You mind sharing that load? 3500+ with that kind of accuracy from the 53g VMAX is pretty awesome.