Maximum bullet weight

[Im2bent]

So I searched the forums and could find no joy. Trying to get a better handle on what determines max bullet weight for a caliber. For instance in 30 cal you can go from 125g to 250g pills. At what point is the bullet to heavy? What happens if you stuff a 250gn in a .308? At some point case neck length or chamber throats come into play? Seems like the higher the weight the higher the bc? But at some point you start to loose something? I am talking strictly long range target shooting not hunting. Do you go for the highest bc and call it a day?

 

[theLBC]

you need to be spin stable, so depending on bullet shape, velocity and twist rate, there is a calculator.

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

so for example, you may find for a .308 with a 1:12 twist rate, 175-180gr is about max, while 1:10 can work with heavier juggernauts.

 

[Dolomite_Supafly]

I designed bullets for a while, specifically for the 300 Blackout. I designed a 265g bullet that was stable in an 8 twist at subsonic velocities and was stable above 1,100 fps in a 10 twist. BC ended up at a calculated .395.

Stability has more to do with length than weight, it is just easier to remember them by weight.

BC is not the end all be all. There are plenty of bullets that are no where near the highest BC but they still perform well. Don't go chasing BC because the differences are marginal at best. Find a bullet that shoots well and use it.

 

[Im2bent]

you need to be spin stable, so depending on bullet shape, velocity and twist rate, there is a calculator.

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

so for example, you may find for a .308 with a 1:12 twist rate, 175-180gr is about max, while 1:10 can work with heavier juggernauts.

I understand that, my question is not about twist vs stabilty but at what point is a bullet to heavy for the caliber. As in is there a point where you can't push that big of a projectile down the barrel efficiently?

 

[KnowNothing256]

As with so many things, it depends. If you’re limited by mag length, then yeah, at some point the bullet eats up too much case volume and is also too heavy, both work against you. Also, you pretty inevitably give up velocity as you add weight, and depending on your range to target, lighter and faster bullets may actually offer better ballistics, even accounting for wind, because they’re in the air for significantly less time.

 

[Steel head]

Mag length
Ability to get a speed with a heavy that can give an advantage over a lighter bullet.
Bullet stability

 

[Im2bent]

Ok let me get more specific. Single feed 375 Cheytac, 33 inch Bartlein, 1:7 twist , Bat action. Why choose a 350 instead of a 407 or heavier? Berger has a 379 solid and a 407 solid....why?

 

[1moaoff]

In some instances the just below REALLY HEAVY for caliber bullets at higher velocity can be a better choice in ballistics.

It takes alot of running the numbers for both drop and drift.... and being realistic in velocity thats easily attainable.

 

[918v]

Ok let me get more specific. Single feed 375 Cheytac, 33 inch Bartlein, 1:7 twist , Bat action. Why choose a 350 instead of a 407 or heavier? Berger has a 379 solid and a 407 solid....why?

It depends on the muzzle velocity and the range you plan in shooting.

 

[jakelly]

Ok let me get more specific. Single feed 375 Cheytac, 33 inch Bartlein, 1:7 twist , Bat action. Why choose a 350 instead of a 407 or heavier? Berger has a 379 solid and a 407 solid....why?

Run the numbers on both, see which yields results that best suit your needs.

In this instance, it seems like the 407 is the winner on paper. However, if your rifle won’t shoot it, you’ll have to use another option.

As a broader answer to your question, for myself, terminal ballistics come into play. Projectiles spun faster track truer while penetrating. Projectiles started faster increase hydrostatic shock and open better / longer. I am also not concerned with external ballistic advantages that require 800+ yds to realize, there’s a 95% chance I will choose the advantages inside of 600 over those after 800.

In short, the case may not have enough displacement to utilize the BC advantage of a heavier and longer projectile. For example, I don’t think that the 6.5 CM is at it’s best with 140s. I think the 120-130s are a better fit for the Creedmoor. You need to step up to ~60gr cases before my assessment matrix favors the 140s. Even then the 130 JLK is a monster.