Twist Rate Stability Calculator

[JKR]

My apologies if this has been discussed ad nauseam already,

Does anyone give any creedence to twist rate stability calculators similar to this one?

https://bergerbullets.com/twist-rate-calculator/

I was able to google the ballistic coefficient of a 575213 PH minie ball which is .145, I know the typical 575213 bullet is sized to .576, weighs in at 565 grains, is 1" tall/long, guesstimated velocity at 950 FPS, twist rate at 48, standard ambient temperature and elevation of 1000'. When I run this number the stability is "marginal".

Playing around with this I found that decreasing the bullet size in weight to 450 grains and height to 3/4" the comfortable stability increased drastically.

So what do y'all think? Is this calculator bunk or are there some sound physics that can be learned from this calculator.

[Carolina Reb]

Bullet stability is controlled by several factors. The three big ones are where the center of gravity is, where the aerodynamic center is, and what is the rotational velocity. There are a lot of assumptions built into those calculators. The CG on hollow base bullets is considerably forward of the assumed position, which makes it more stable.

After LOTS of long range testing, Enfield and Springfield experimentally derived the slowest practical twist for 58 cal. bullets. Enfield came up with 1 in 78, while Springfield decided on 6 inches faster. The reason for all this work is that at long range gyroscopic drift sets in and causes the bullet to drift right. The faster the twist, the more the drift. (Also, the faster the barrel fouls.) Rather than design compensating sights, they went to the slowest practical twist to minimize drift and fouling.

1 in 48 is a pretty fast twist for muskets. Enfield went to it for rifles and musketoons because with issue ammo the shorter barrels reduced muzzle velocity velocity enough that 1 in 78 didn't shoot as well as it did with 39 inch barrels. Since we load our own ammo, it's easy to bump up the charge a little, or choose a more stable bullet (like the international, Hodgden or semi-wadcutter)

It's all a tradeoff.