Shot-to-Shot Variation in Muzzle Velocity (MV) and Ballistic Coefficient (BC)

[nksmfamjp]

That's some cool stuff....I also think I just saw the big brother to my Labradar!

 

[DocUSMCRetired]

Questions: What causes the BC difference in the bullets?
Is it physical variation like weight and bearing surface length, meplat variance of each bullet?
Or is the BC difference dependent on the muzzle velocity variation?
So sorting bullets and meplat trimming does help!?

Slight variances in manufacturing. On a microscopic level you will always have tiny variances in how a bullet forms.

 

[epoletna]

Really good stuff! Thanks for posting. I sure would like to get a SD of 5 in any of my rifles!

 

[BMC15]

Interesting! So if you have 2 different rounds but they have the same bullet will the BC be the same?

 

[DocUSMCRetired]

Interesting! So if you have 2 different rounds but they have the same bullet will the BC be the same?

Two different bullets out of the exact same box could very likely have the same BC, or fall inside the specific BC SD percentage.

 

[BMC15]

What about 2 ammo suppler ( Eley, Lapua) for example using the same bullet will the BC be the same? If it's only the bullet itself that makes up the BC.

 

[DocUSMCRetired]

What about 2 ammo suppler ( Eley, Lapua) for example using the same bullet will the BC be the same? If it's only the bullet itself that makes up the BC.

Probably different as they are two different runs. Unless the lot number matches on the back end.

 

[BMC15]

Thanks I don't know why some supplier are so secretive about their BC. I notice the Lapua says that all their 22lr are .172. I guess that means that regardless of the different styles they have the same bullet.

 

[Bravo 4]

Thanks I don't know why some supplier are so secretive about their BC. I notice the Lapua says that all their 22lr are .172. I guess that means that regardless of the different styles they have the same bullet.

What he is saying is that due to the manufacturing processes and such no 2 bullets will be 100% the same. This is an ever so slight difference and really only matters at long distance. You can even look at two Berger OTM or Sierra Matchkings from the same box and see the difference in the tips (one of the places the dimensions will be different). That is why guys trim the meplats or tip these bullets for comp/target shooting, to help make them more consistent.

Doc,
What have you seen as far as turned bullets? Some of what I've read say more consistent that cup-n-core bullets swagged in dies.

 

[DocUSMCRetired]

What he is saying is that due to the manufacturing processes and such no 2 bullets will be 100% the same. This is an ever so slight difference and really only matters at long distance. You can even look at two Berger OTM or Sierra Matchkings from the same box and see the difference in the tips (one of the places the dimensions will be different). That is why guys trim the meplats or tip these bullets for comp/target shooting, to help make them more consistent.

Doc,
What have you seen as far as turned bullets? Some of what I've read say more consistent that cup-n-core bullets swagged in dies.

It really varies on how precise and how many passes or basically how much time they want to spend on them. Some are rougher, and some are smooth as butter. Just run your fingernail across different brands.

 

[Bravo 4]

It really varies on how precise and how many passes or basically how much time they want to spend on them. Some are rougher, and some are smooth as butter. Just run your fingernail across different brands.

Have y'all tested any to see how that effects the BC consistency? Brings other variables into the mix.

 

[DocUSMCRetired]

Have y'all tested any to see how that effects the BC consistency? Brings other variables into the mix.

Tons of testing, and design work on solids. We have a lathe in our lab so we can make them on demand.

 

[Bravo 4]

Anything that I can read on this?

 

[DocUSMCRetired]

Anything that I can read on this?

Probably will be in a future publication. Apologies.