223 bullet stability chart w BC and bullet lengths

[BobbyJ]

I put together a chart on a variety of 223 bullets and ran them all through the JBM ballistics chart. I corrected for any that have plastic tips. Color coded it to show which bullets work best with twist rates.

Not sure how well it holds up to real life shooting. I did check some against what the manufacturer recommend in terms of twist rates and they seem close enough for a rough idea what will work with your gun. Let me know if there are any errors on BC or bullets.

The JBM simply subtracts 100 percent of the polymer tips length from the OAL of the bullet which is not quite correct as there is some length and mass to them. Some subtraction is needed but a fraction, as its a bit too aggressive in the assumption that it makes not difference. I'm going to run the tips using a different formulae to dial it in a bit.

 

[K22]

Thanks for the chart - very interesting.

However, if "BT" means boat tail, then both the 55 and 60 vmax are flat base, not boat tail.

 

[BobbyJ]

Thanks for the chart - very interesting.

However, if "BT" means boat tail, then both the 55 and 60 vmax are flat base, not boat tail.

Good Catch! Fixed it thanks.

 

[Acyr]

Need to add 80 grain bullets

 

[BobbyJ]

Need to add 80 grain bullets

Which 80 gr you want?

 

[Doom]

The JBM (Miller) calculator is for boat tail bullet design. It doesn't work well for flat based bullets. You might want to check out Berger's site for more info.

 

[lawman29]

52 SMK

 

[Acyr]

Which 80 gr you want?

Berger 80.5 Fullbore and 85.5 Hybrid please

 

[Kracken McGraw]

Hornady 75 grain bthp also, Thanks!

 

[Kracken McGraw]

I’m kinda surprised at the 69 SMK with the 8 twist.

 

[karrarararararar]

Length on the 90 smk is 1.171

 

[762willdo]

73 grain Berger

 

[karrarararararar]

Might want to double check your lengths. The 69 and 77 smk are also incorrect according to JBM

 

[BobbyJ]

The JBM (Miller) calculator is for boat tail bullet design. It doesn't work well for flat based bullets. You might want to check out Berger's site for more info.

I did look at it but they don't have a decent chart of FB bullets just a few. From what I read you could look at the SG of the next faster twist. I'm going to look at more in depth calculation using actual bullet dimensions to better nail down those pesky Flat base bullets. Also look at real world result from some of the bullets. I know the 77 SMK will key hole from a 1/9 twist and the chart has it at 1.19 so its not far off on those. Again it depends on the altitude, humidity, and velocity so the chart will not be perfect more of a quick guide.

Bison Ballistics says its pretty close as they used data from both flat and boatails.
"Is the calculator accurate for flat based bullets?

More or less. The data that Miller used to crate the rule consisted of data from boattail and flat-based projectiles. The data for boattail bullets is a better fit than that for flat based bullets, but it's still a reasonably good approximation. As with any calculation, use an appropriate margin of safety, as real life sometimes intervenes."

Trying to work out a fudge factor for FB bullets. It looks like maybe 1 to 1.5 twist rate higher if its FB.
I did put in 3 berger flat based bullets . On the 52 Berger they recommend a minimum of 1/14 twist on my chart you can see its barely stabilized at 1.037. But since its not a BT but a Flat base its probably acting like if it were shot from a 1/13 or 1/12. So for now just have to fudge it.

 

[BobbyJ]

Might want to double check your lengths. The 69 and 77 smk are also incorrect according to JBM

Thanks, those numbers came out of Quickload.

I think that is what they are suppose to be .898 for the 69 SMK but. I measure a bunch and they vary from .896" to .904" I'd say the Average is .902"
JBM has .900" Which not sure how many samples they measured to get that. I'll bump it to .900"

Not sure whos data to trust. Quick load has been building up a database for 20 years. They can have errors but wondering if they get their specs from the Manufacture on how long they should be. Then a guy gets a batch that is out of spec and sends that measurement to JBM, not sure on that.

If anyone here has 77 smk or any other bullet listed that you think might be off could you measure at least 10 or them for an average? Thanks.

I would rather use the manufactures data as batch to batch there is some variability. Some of my SMKs were under .898" some over. Based on my small sample of 10 or so JBM is closer

 

[BobbyJ]

Length on the 90 smk is 1.171

Can you verify it by measure some actual bullets? I have own many of them and can double check but I don't own any 90s. I don't know that I trust JBM numbers over Quickload just yet.

I saw quite a bit of variation on actual 69 SMKs. Would be nice of the companies published this info.

 

[BobbyJ]

I can expand the chart to all the twists but I just stuck with ones that are available. 1/13 1/11 1/10 not so common.

BTW the BCs I have listed even if wrong do not affect the calculations. It only would affect it if someone wanted to know what their reduced BC would be if their SG was say 1.2 and not 1.5+.

I'll still fix them if needed. Altitude, Temp and Velocity are the variables that can through this off for some people living at say 5,000 feet.
I will put in a coversion for those. Off the top of my head its like

Velocity -Higher = inc SG 0.1 - .2
Temp - Higher = inc SG but like .1 to .2
Altitude - Higher = inc SG. Ie change from 1000 to 5000 feet SG can go up .15 to .4.

The faster the twist the more all of these affect it .

A 1/14 is going to be more resistant to these variables than a 1/7 twist.

 

[karrarararararar]

Can you verify it by measure some actual bullets? I have own many of them and can double check but I don't own any 90s. I don't know that I trust JBM numbers over Quickload just yet.

I saw quite a bit of variation on actual 69 SMKs. Would be nice of the companies published this info.

I don't have 90's, but I would trust the litz numbers

 

[FeMan]

Nice!

 

[BobbyJ]

52 SMK

Its there, the other 52 berger is a flat bottom which actually will stabilize more like it was shot from a faster twist so even though its 1/14 is bad on the chart it will act like the 1/12 shooting.
52 smk not quite as good in 1/14. The chart is confusing cause I included the flat base too.